AST-A 222

Find the range limit of using type Ia supernova to measure distance.

11 million ly

What is the average density of interstellar gas, and interstellar dust?

1 atom per cm3 for gas. Dust was around 100-1000 particles per km3

Find the density of a neutron star.

1017 kg/m3

Describe the properties of superclusters?

10^16 Solar Masses. Looks like made of filaments or inkblots Typical diameter of 150 Mlyr.

Find the total luminosities and the masses of the visible portions of spiral galaxies.

10^9 to 10^12 Solar Masses, and 10^8 and 10^11 Solar Luminosities.

Find the typical age, metallicity, and rotation properties of stars in the stellar halo.

11 to 13 billions years old contains globular clusters. Has metallicity 1/100 of thin disk. Rotation is very slow

how long do sunspot cycles take?

11 years for one cycle, and then they swap magnetic polarities, so technically, it's 22 years to complete a full cycle

Fusion of protons can occur in the center of the Sun only if the temperature exceeds what?

12 million K.

Where do stars form?

Molecular clouds

Where did Earth's water come from?

Moon-forming impact left water vapor in the hot atmosphere, which condensed into oceans. Impacts brought ice to the surface, which was either vaporized or condensed.

Find the mass-luminosity relation.

More mass = more luminosity L is proportional to M^3.5

Why were there more quasars long ago (far away) than there are today (nearby)?

More matter available in the past than in the present

Explain the Hubble's law in the context of the expansion of the Universe.

Objects father away are moving away faster meaning that the universe is expanding

Explain standard bulbs.

Objects that all have the same luminosity. Compared to apparant brightness and known luminosity can give distance

quasar

Objects with large redshifts that appear star-like but have no radio emission. Have bright in the infrared and X-ray bands too. Objects referred to as quasi-stellar-objects (QSOs)

How did we build the period-luminosity relation for Cepheid variables?

Observations

What are habitable planets? Why is it hard to find them?

Planets with liquid water, breathable atmosphere. Our detection techniques select heavily for heavy, hot planets.

What is an example of a cepheid variable?

Polaris, the North Star, is a cepheid variable that, for a long time, varied by one tenth of a magnitude, or by about 10% in visual luminosity, in a period of just under 4 days. Recent measurements indicate that the amount by which the brightness of Polaris changes is decreasing and that, sometime in the future, this star will no longer be a pulsating variable. This is just one more piece of evidence that stars really do evolve and change in fundamental ways as they age, and that being a cepheid variable represents a stage in the life of the star.

Is our Sun a population I or a population II star?

Population 1

Where is the infalling material from?

Possibly another star in the system or the remnants of its outer layers if they blew off. Also random ISM stuff

What is the hydrogen-burning shell of a star? What energy triggers the hydrogen fusion in the hydrogen-burning shell

Post-main sequence stars have a helium-burning shell surrounded by a hydrogen-burning shell. The reason is because once the Hydrogen in the core is burnt up, the core contracts and heats up causing an outer shell to fuse

What causes spectral broadening?

Pressure in a star, the Zeeman effect, star rotation

If all the variable stars in the Magellanic Clouds are at roughly the same distance, then any difference in their apparent brightnesses must be caused by what?

differences in their intrinsic luminosities

How does the cosmological principle apply to the Hubble constant?

because the universe is isotropic & homogenous the hubble constant is constant no matter what point in space it is

The tiny interstellar dust grains absorb some of the starlight they intercept. But at least half of the starlight that interacts with a grain is merely scattered, that is, it is redirected rather than absorbed. Since neither the absorbed nor the scattered starlight reaches us directly, both absorption and scattering make stars look dimmer. The effects of both processes are called

interstellar extinction (Figure 20.14). Astronomers first came to understand interstellar extinction around the early 1930s, as the explanation of a puzzling observation. In the early part of the twentieth century, astronomers discovered that some stars look red even though their spectral lines indicate that they must be extremely hot (and thus should look blue). The solution to this seeming contradiction turned out to be that the light from these hot stars is not only dimmed but also reddened by interstellar dust, a phenomenon known as interstellar reddening

Astronomers refer to all the material between stars as what?

interstellar matter; the entire collection of interstellar matter is called the interstellar medium (ISM). Some interstellar material is concentrated into giant clouds, each of which is known as a nebula (plural "nebulae," Latin for "clouds"). The best-known nebulae are the ones that we can see glowing or reflecting visible light.

What's the issue of this method?

Doesn't account for mass outside of the suns orbit only within

How can we measure the speed of a galaxy?

Doppler shift

How can we measure the rotation of a star?

Doppler shift at the leading and trailing edge of the star.

Describe redshift and blueshift.

Doppler shift makes wavelength shifts based on radial velocity and direction of motion. If motion is away it's redshift as the waves get longer. If towards then it's blueshift as the waves get shorter

How was the first exoplanet around a Sun-like star discovered?

Doppler wobble

Why is the Galaxy flatten disk shape?

Due to angular momentum is flattened/collapsed into a disk

William Herschel

He discovered the planet Uranus, built several large telescopes, and made measurements of the Sun's place in the Galaxy, the Sun's motion through space, and the comparative brightnesses of stars.

What can predict solar storms that might impact earth?

Helioseismology has become an important tool for predicting solar storms that might impact Earth. Active regions can appear and grow large in only a few days. The solar rotation period is about 28 days. Therefore, regions capable of producing solar flares and coronal mass ejections can develop on the far side of the Sun, where, for a long time, we couldn't see them directly.

What does Helioseismology specifically show us?

Helioseismology has shown that convection extends inward from the surface 30% of the way toward the center; we have used this information in drawing Figure 16.15. Pulsation measurements also show that the differential rotation that we see at the Sun's surface, with the fastest rotation occurring at the equator, persists down through the convection zone. Below the convection zone, however, the Sun, even though it is gaseous throughout, rotates as if it were a solid body like a bowling ball. Another finding from helioseismology is that the abundance of helium inside the Sun, except in the center where nuclear reactions have converted hydrogen into helium, is about the same as at its surface. That result is important to astronomers because it means we are correct when we use the abundance of the elements measured in the solar atmosphere to construct models of the solar interior. Helioseismology also allows scientists to look beneath a sunspot and see how it works.

What is an alpha particle?

Helium Nucleus

What is the faint young sun paradox?

Early in Earth's life, the Sun's luminosity was on 70% as intense as it is today, yet Earth still had liquid water when you would expect it to be ice.

Describe the movement of a star on the H-R diagram during the triple-alpha process.

It leaves the main sequence and travels to the top right of the diagram where it dips and peaks a lot

Find the relation between the number of quasars and the age of the universe.

Has been declining ever since beginning of the universe

Why do quasars look like stars?

Have extremely high luminosities

List observational characteristics of quasars

Have jets that shoot out perpendicular to them, emit lots of energy, radio and gamma radiation, high luminosity

Find the location, the amount of heavy elements, and the age of Pop I stars.

Located in thin disk. Aged from 1 million to 10 bullion years. 1-4% metal

cosmological principle on the expanding universe

universe is homogeneous and isotropic. As a result, the expansion rate must be the same everywhere during any epoch of cosmic time.

What is dark energy?

unknown force that is causing expansion of universe

Relativistic formula for the Doppler shift for distant objects

v/c = ((z+1)^2-1)/((z+1)^2+1)

There are also some stars in the lower-left corner of the H-R diagram, which have high temperature and low luminosity. If they have high surface temperatures, each square meter on that star puts out a lot of energy. How then can the overall star be dim? It must be that it has a very small total surface area; such stars are known as what?

white dwarfs (white because, at these high temperatures, the colors of the electromagnetic radiation that they emit blend together to make them look bluish-white).

What is a visual binary system?

A binary system where you can see both stars through a telescope

What is an eclipsing binary system?

A binary system whose orbital plane is parallel to our line of sight

Supermassive black holes

A black hole that contains more mass than the death of any 1 star could make

Halo

A classic Xbox game. A sphere of old faint stars. Distance at least 150,000 ly from center. Contains thin&Thick disk and nuclear bulge

Nebulae

A cloud of gas and dust

What are the most massive reservoirs of interstellar medium?

Giant Molecular Clouds

H-R diagram

(Hertzsprung-Russell diagram) a plot of luminosity against surface temperature (or spectral type) for a group of stars

Find mass estimates for typical protoplanetary disks.

0.5-1 Mj (mass of jupiter) for solar sized stars

Find the range limit of using cepheids to measure distance.

0-110 million ly

Describe four different scenarios of the evolution of the Universe, and discuss the difference among them.

1. Density higher than critical density causing big crunch 2. Density higher than critical density causing infinite deacceleration but still expanding 3. Density equals critical density so universe constant expansion 4. Density less than critical density so universe expansion accelerates

How galaxy forms

1. Primordial hydrogen cloud 2. Cloud collapses under gravity 3. Large bulge of ancient stars dominate galaxy 4. Disk galaxy and companion 5. Smaller galaxy falls into disk galaxy 6. Bulge inflates with addition of young stars and gas

Name five characteristics of a star that can be determined by measuring its spectrum. Explain how you would use a spectrum to determine these characteristics.

1.) Temperature: according to Wien's law, the signatures of spectral lines gives the temperature of a star 2.) Chemical composition: for two stars to have identical temperature and pressure, stronger lines mean that there are more atoms in the stellar photosphere absorbing light 3.) Atmospheric pressure: Spectra of stars of the same temperature but different atmospheric pressure show different broadening in spectral lines. The low pressure affects the spectrum in two ways: i.) The more collision in the star's photosphere leads to broader spectral lines. Low pressure stars show narrower spectral lines than high pressure stars. ii.) Ionized atoms have different spectra from atoms that are neutral. The ionization of atoms in a star's outer layer is caused mainly by photons, and the amount of energy carried by photons is determined by temperature. But the time duration of ionized atoms depend in part on pressure. 4.) Radial Velocity: the Doppler Effect must be considered for the moving stars with respect to the earth. If the star is moving towards earth, then all the spectral lines of the moving star are shifted towards the blue spectrum. The shift is greater for the fast moving star. Such motion, along the line of sight between the star and observer, is called radial velocity. 5.) Rotation: speed of rotation of a star is also measured by using the doppler effect. Due to doppler effect, the lines in the light that come from the side of the star rotating towards us are shifted to shorter wavelengths and the lines in the light that come from the side of the star that is rotating away from us is shifted to longer wavelengths

After what Universe age, will the galaxy evolve peacefully?

1/2 its current age

How many stars are there in our Milky Way Galaxy?

100 billion

Find the number of stars in the milky way galaxy.

100 to 400 billion

When was the last supernova observed in our Milky Way?

1604

When was the first telescope invented?

1608 by Hans Lippershey

Recall the proton-proton chain reaction.

2 protons collide to form a deuterium atom which consists of a proton and a neutron. When the deutrium atom collides with another proton it created helium 3. When a helium 3 collides with another helium 3 we get helium 4 and 2 seperate protons

What is a safe distance for life to be from a supernova explosion?

50-100 ly

Find the number of grains of sand on Earth.

7.5*10^18

What's the density and temperature of the Local Fluff?

7000K and 0.3 Hydrogen atoms/cm^3

Find the typical lifetime of a protoplanetary disk.

<10 million years

What are cosmic rays?

A cosmic ray is a highly energetic proton or nuclei that travels close to the speed of light

what is a visual binary?

A binary star system in which both of the stars can be seen with a telescope is called a visual binary

What are luminous stars that are red and actually are enormous?

A few of the very luminous stars, those that are also red (indicating relatively low surface temperatures), turn out to be truly enormous. These stars are called, appropriately enough, giant stars or supergiant stars. An example is Betelgeuse, the second brightest star in the constellation of Orion and one of the dozen brightest stars in our sky.

What is a stellar cluster?

A group of stars

What is a point mass?

A mass with no volume

What is left after a type II supernova explosion?

A neutron star or even a black hole

What's a positron?

A positron is the electron's antiparticle. It has the same mass but opposite charge of the electron. It annihilates the electron on contact and creates energy.

What is a reflection nebula? What color of light does a reflection nebula usually scatter?

A reflection nebula is a cloud of interstellar dust that reflects light. It appears blue mostly because of the stellar reddening, which means the blue light is more effectively scattered than red light

What are RR Lyrae stars?

A related group of stars, whose nature was understood somewhat later than that of the cepheids, are called RR Lyrae variables, named for the star RR Lyrae, the best-known member of the group. More common than the cepheids, but less luminous, thousands of these pulsating variables are known in our Galaxy. The periods of RR Lyrae stars are always less than 1 day, and their changes in brightness are typically less than about a factor of two.

What does "self-similarity" mean?

A small part of an object is similar to the larger part of itself

What is a continuous spectrum?

A spectrum uninterrupted at all wavelengths.

What is a star defined as?

A star is defined as an object that during some part of its lifetime derives 100% of its energy from the same process that makes the Sun shine—the fusion of hydrogen nuclei (protons) into helium. Objects with masses less than about 7.5% of the mass of our Sun (about 0.075 MSun) do not become hot enough for hydrogen fusion to take place. Even before the first such "failed star" was found, this class of objects, with masses intermediate between stars and planets, was given the name brown dwarfs.

What is a spectroscopic binary?

A star like Mizar A, which appears as a single star when photographed or observed visually through the telescope, but which spectroscopy shows really to be a double star, is called a spectroscopic binary.

giant star

A star of exaggerated size with a large, extended photosphere

What precision do we need to detect gravitational waves?

A strong gravitational wave will produce a displacement on the order of 10-18 meters, which is 1000 times smaller than the proton

What is a protostar?

A young star that is still collecting mass but has not yet fused molecules in its core

How much fraction of material in a molecular cloud will turn into stars?

About 1%

What's the density and temperature of the Local Bubble?

About 7000 K and 0.01 atoms/cm^3

What is ISM (interstellar medium) made of?

About 99% of the material between the stars is in the form of a gas—that is, it consists of individual atoms or molecules. The most abundant elements in this gas are hydrogen and helium (which we saw are also the most abundant elements in the stars), but the gas also includes other elements. Some of the gas is in the form of molecules—combinations of atoms. The remaining 1% of the interstellar material is solid—frozen particles consisting of many atoms and molecules that are called interstellar grains or interstellar dust (Figure 20.2). A typical dust grain consists of a core of rocklike material (silicates) or graphite surrounded by a mantle of ices; water, methane, and ammonia are probably the most abundant ices.

Find the typical size of a Quasar.

About the size of our solar system ~ 5 light hours

The Universe is expanding. Is the expansion of the Universe accelerating or decelerating?

Accelerating

What are AGNs?

Active Galactic Nuclei, they're regions of high activity in the centers of galaxies

What is the Henyey track?

After the end of the Hayashi track for stars less than 0.5 solar masses. Represents a slow collapse and almost hydrostatic equilibrium that is nearly horizontal to main sequence

Find the typical age, metallicity, and rotation properties of stars in the thick disk.

Age: Age of about 11 billion years older than thin disk but younger than halo Has an intermidiate metallicty compared to thin disks high and halos low Intermiediate to lower rotation

Find the typical age, metallicity, and rotation properties of stars in the thin disk.

Age: Up to 10 billion years Metallicity is 1-4% of total mass Rotate flat in the galactic plane

Why do the hotter stars show fewer spectral lines?

All the hydrogen is ionized so the electrons do not orbit the protons. Therefore they cannot drop to lower energy levels as they are not in one to begin with.

Why is a red giant cooler than it was on its main-sequence phase?

Although the star is producing more energy, the energy per surface area decreases meaning that the surface temperature also decreases.

What is the longest step of the sun's nuclear reaction process?

Although, as we discussed, the first step in this chain of reactions is very difficult and generally takes a long time, the other steps happen more quickly. After the deuterium nucleus is formed, it survives an average of only about 6 seconds before being converted into 3He. About a million years after that (on average), the 3He nucleus will combine with another to form 4He.

What is a light curve?

Amount of light we're receiving per unit time.

What is the mass-to-light ratio of a star?

Amount of mass a star has to how much luminosity it has. Higher ratio for lower mass stars

At a temperature of 6 billion (6 × 109) K, what can be created if two typical photons collided. What if the temperature is higher than 10^14K?

An electron and positron. At 10^14 it is hot enough to produce protons and antiprotons

What is spin-flip transition and what causes it?

An electron in neutral hydrogen absorbs energy and its spin is flipped to be oriented with the proton. The electron then flips back and releases the energy as a 21 cm line. It absorbs energy

What is a radioactive element?

An element with an unstable nucleus that is likely to decay

What is an emission nebula? What color of light does an emission nebula usually emit?

An emission nebula is one that emits its own light. They usually appear redder because of hydrogen abundance and their lower wavelength

multiverse

An idea that our universe is one of countless universes some which may have different laws so that we don't exist or that nothing exists as in they have no structure. An infinite possibilty of universes. If you're confused just watch Spiderman into the spider-verse

What is a black hole?

An object that has an escape velocity higher than the speed of light

What is a face-on or an edge-on orbit?

An orbit where the orbital plane is parallel to our line of sight

What is the field of view (FOV) of a telescope?

Angular measurement of how much sky the telescope can see

What are organic molecules?

Any molecule containing carbon-hydrogen bonds

What's an eclipsing binary?

Binary system where the orbital plane is parallel to our line of view, so we see them eclipse each other

Where can we find an intermediate-mass black hole?

Anywhere you find very high mass stars (or their remnants)

How can we measure the Luminosity of a star?

Apparent magnitude and the distance

What's the relation between apparent magnitude and absolute magnitude?

Apparent magnitude is our perceived brightness of a star and absolute magnitude is the perceived brightness from 10 parsecs away or 32.6 light-years.

Central Bulge

Area close to galactic center (10,000 ly) where stars are no longer confined to the disk. Milky ways bulge is twice as long as is wide

Why are inertial mass and gravitational mass identical?

As a result of the equivalence principle, a gravitational acceleration is identical to a normal acceleration, and therefore an inertial mass is the same as a gravitational mass.

Suppose you want to determine whether a star is a giant. A giant star has a large, extended photosphere. Because it is so large, a giant star's atoms are spread over a great volume, which means that the density of particles in the star's photosphere is low. What does this result in?

As a result, the pressure in a giant star's photosphere is also low. This low pressure affects the spectrum in two ways. First, a star with a lower-pressure photosphere shows narrower spectral lines than a star of the same temperature with a higher-pressure photosphere. The difference is large enough that careful study of spectra can tell which of two stars at the same temperature has a higher pressure (and is thus more compressed) and which has a lower pressure (and thus must be extended). This effect is due to collisions between particles in the star's photosphere—more collisions lead to broader spectral lines. Collisions will, of course, be more frequent in a higher-density environment. Think about it like traffic—collisions are much more likely during rush hour, when the density of cars is high.

What about the other stars on the H-R diagram—the giants and supergiants, and the white dwarfs? As we will see in the next few chapters, these are what main-sequence stars turn into as they age: They are the later stages in a star's life. What does this mean?

As a star consumes its nuclear fuel, its source of energy changes, as do its chemical composition and interior structure. These changes cause the star to alter its luminosity and surface temperature so that it no longer lies on the main sequence on our diagram. Because stars spend much less time in these later stages of their lives, we see fewer stars in those regions of the H-R diagram.

What is precession?

As an object precesses, its axis of rotation travels around a circle

What will happen when the gravity of a neutron star is strong enough to break neutron degeneracy?

Black hole is formed

The sun's energy is from nuclear fusion, which only emits gamma-ray photons. Where are visible photons from?

As photons try to escape the solar interior they are absorbed by atoms and reemitted at lower energy levels. Visible photons are from the photosphere.

Suppose a planet forms a few AU away from the protostar, presumably due to the gathering together of matter from the disk. As the planet grows in mass, what happens?

As the planet grows in mass, the process clears out a dust-free region in its immediate neighborhood. Calculations also show that any small dust particles and gas that were initially located in the region between the protostar and the planet, and that are not swept up by the planet, will then fall onto the star very quickly in about 50,000 years. Matter lying outside the planet's orbit, in contrast, is prevented from moving into the hole by the gravitational forces exerted by the planet. (We saw something similar in Saturn's rings, where the action of the shepherd moons keeps the material near the edge of the rings from spreading out.) If the formation of a planet is indeed what produces and sustains holes in the disks that surround very young stars, then planets must form in 3 to 30 million years. This is a short period compared with the lifetimes of most stars and shows that the formation of planets may be a quick byproduct of the birth of stars.

Explain why low-temperature and dense clouds (cores) are ideal places to trigger star formation.

At low temperatures, the outward pressure is easily counteracted by the gravity of the collapsing particles so that it can condense.

Describe the principle of redshift in the context of the expansion of the Universe

As things get father away there redshift spectrum is stretched so as the universe expands everythings redshift is stretching

Why do you think astronomers have suggested three different spectral types (L, T, and Y) for the brown dwarfs instead of M? Why was one not enough?

Astronomers have classified the brown dwarfs in three spectral types: L, T, and Y instead of M. Astronomers classified the stars according to their temperature and signatures of elements in the spectrum. In M type, there are strong lines of neutral metals and molecular bands of titanium oxide. In L type, most lines in the spectrum are from Metal hybrid, alkali metals. In T type, there are methane lines. In Y type, there are Ammonia lines. Temperature of objects changes with lines in spectrum. Astronomers get different spectrum in dwarf stars. So, they classify them to three different classes

Why is the sun such a strong and complicated magnet?

Astronomers have found that it is the sun's dynamo (a machine that converts kinetic energy into electricity) that generates the magnetic field. The sun does this by taking the churning of turbulent layers of ionized gas as a source of kinetic energy and use them to generate electric currents, which in turn generate magnetic fields

How bright is the most luminous supernova compared to the Sun?

At maximum brightness, 10 billion times the luminosity of the sun

Quasars & the Hubble Law

Astronomers were unsure if Quasars obeyed Hubble's law because their redshifts implied they were at large distances. If they didn't obey the large redshift means large distance then they could be closer with lower luminosity. Quasars were found in centers of galaxies and since galaxies follow Hubble's law then so do the objects within them

first few minutes of the universe

At 0.01s the universe was at 100 billion K, cooled to 1 billion K in 3 minutes took a couple hundred thousand years to reach 3000k and has continued to cool. The photons at those temperatures could collide and produce material particles

Find the mass relation between black holes and their host galaxies.

Black holes are around 1/200 mass of host galaxy

Calculations show that accretion can drive the rapid growth of planets—small, dust-grain-size particles orbiting in the disk collide and stick together, with the larger collections growing more rapidly as they attract and capture smaller ones. Once these clumps grow to about 10 centimeters in size or so, they enter a perilous stage in their development. what happens?

At that size, unless they can grow to larger than about 100 meters in diameter, they are subject to drag forces produced by friction with the gas in the disk—and their orbits can rapidly decay, plunging them into the host star. Therefore, these bodies must rapidly grow to nearly 1 kilometer in size in diameter to avoid a fiery fate. At this stage, they are considered planetesimals (the small chunks of solid matter—ice and dust particles—that you learned about in Other Worlds: An Introduction to the Solar System). Once they survive to those sizes, the largest survivors will continue to grow by accreting smaller planetesimals; ultimately, this process results in a few large planets.

Steps of Energy to Matter

At the highest temperatures gamma rays became electrons and positron. As temperature decreases the protons and neutrons can come together to make nuclei. When even coolor electrons settled down with nuclei to make neutral atoms

Discuss the atmospheric distortion on a photometric image.

Atmosphere interacts with light being emmitted by object in space causing image to be blurred

Where is hot coronal gas?

It is present mainly where magnetic fields have trapped and concentrated it

What is an astrometric binary system?

BInary system where one star is invisible but can be seen through its influence on the other

Describe the properties of SBa galaxies

Barred version of Sa

Describe the properties of SBb galaxies

Barred version of Sb

Describe the properties of SBc galaxies

Barred version of Sc

Astronomers use the patterns of lines observed in stellar spectra to sort stars into a spectral class. What are the spectral classes, and what do they measure?

Because a star's temperature determines which absorption lines are present in its spectrum, these spectral classes are a measure of its surface temperature. There are seven standard spectral classes. From hottest to coldest, these seven spectral classes are designated O, B, A, F, G, K, and M. Recently, astronomers have added three additional classes for even cooler objects—L, T, and Y.

Why does a red giant/supergiant lose some of its mass?

Because it swells in size, the gravity can't hold the outer layers of the star due to the radiation pressure.

What's the critical difference between these three populations?

Biggest difference is metallicty

What is a spectroscopic binary system?

Binary system that can only be noticed as a binary through the spectra of the stars

Giant molecular clouds have densities of hundreds to thousands of atoms per cm3, much denser than interstellar space is on average. As a result, though they account for a very small fraction of the volume of interstellar space, they contain a significant fraction—20-30%—of the total mass of the Milky Way's gas. Because of their high density, molecular clouds do what?

Because of their high density, molecular clouds block ultraviolet starlight, the main agent for heating most interstellar gas. As a result, they tend to be extremely cold, with typical temperatures near 10 K (−263 °C). Giant molecular clouds are also the sites where new stars form, as we will discuss below.

Why does cosmic dust radiate most of its energy at infrared to microwave frequencies?

Because of their small size and low temperatures

During the protogalactic cloud collapse, what will happen for stars born before the collapse?

Become halo stars

What conditions are required before proton-proton chain fusion can start in the Sun?

Before a proton- proton chain can begin, the problem of electrostatic repulsion must be eliminated, as when the two nuclei are close enough, the strong force tries to keep them apart, so high temperatures and densities are required to overcome this force, as it allows the nuclei to move at high enough speeds to fuse together

Describe the rate of star formation and black hole growth in the universe's history.

Both have been declining since the start of the universe less stars form so less stars available to go supernova to make more black holes

population I Star

Bright blue stars in the spiral arms. Found only in the disk and have mainly circular orbits around galactic center. Have wide ranges of age.

Would a red star have a smaller or larger magnitude in a red filter than in a blue filter?

Brightness of a red star is more in red filter and brightness of a red star is less in blue filter. In using magnitude, the system goes backward such that the larger the magnitude, the fainter the object. So, a red star has a smaller magnitude in red filter than a blue filter

What are light curves?

Brightness vs time

How do we know that star formation in the cosmos or in the milky way galaxy began very early?

Distant galaxies already having heavy elements, old elliptical galaxies having old stars within them

How do you calculate a color index?

By agreement among astronomers, the ultraviolet, blue, and visual magnitudes of the UBV system are adjusted to give a color index of 0 to a star with a surface temperature of about 10,000 K, such as Vega. The B-V color indexes of stars range from −0.4 for the bluest stars, with temperatures of about 40,000 K, to +2.0 for the reddest stars, with temperatures of about 2000 K. The B-V index for the Sun is about +0.65. Note that, by convention, when taking the difference between the two magnitudes to calculate the color index, the B-V index is always the "bluer" minus the "redder" color.

How can we define the birth and the death of a star?

By nuclear fusion starting and stopping

How do we know there is a black hole in the center of the milky way galaxy?

By studying the orbit of stars close to the center of the galaxy

What is the 21cm line?

Change in electron spin orientation emits 21 cm wavelength

Why do the distant galaxies not look like the nearby galaxies?

Distant galaxies are in different stages of their evolution

What must be true if the sun does not collapse due to the force of gravity?

Calculations show that, in order to exert enough pressure to prevent the Sun from collapsing due to the force of gravity, the gases at its center must be maintained at a temperature of 15 million K. Think about what this tells us. Just from the fact that the Sun is not contracting, we can conclude that its temperature must indeed be high enough at the center for protons to undergo fusion.

Masses of Galaxies

Can be calculated by observing satellite galaxies and using good ol' keplers third law to get mass.

Describe the properties of elliptical galaxies

Can have a lot of very little mass can be shaped like a sphere or be a bit flattened. Contains mostly holder stars

Describe the black hole Influence on the formation of stars in the galaxy.

Can help star formation by compressing nearby gas or inhibit star formation by heating up gas and destroying molecular clouds

What can we learn from the abundance of deuterium?

Can help us learn about the density of the early universe

How much fraction of mass will the Sun lose when the Sun reaches the point of the helium flash.

Can lose as much as 25% of its mass

What are the "environmental influences" of galaxy evolution?

Cannibilizing/Merging/Colliding with other galaxies

What elements will be produced during the triple-alpha process?

Carbon and oxygen

What are Cepheid variables? Describe their property (spectral class, period, etc.).

Cepheid are yellow giants ( F→ K). 3-15 days, luminosity is 1000→ 10,000 bigger than the sun, their variation is from a few percent to a factor of 10.

What are Cepheids?

Cepheids are large, yellow, pulsating stars named for the first-known star of the group, Delta Cephei.

It is in these dark regions of space, protected from starlight, that molecules can form. Chemical reactions occurring both in the gas and on the surface of dust grains lead to what?

Chemical reactions occurring both in the gas and on the surface of dust grains lead to much more complex compounds, hundreds of which have been identified in interstellar space. Among the simplest of these are water (H2O), carbon monoxide (CO), which is produced by fires on Earth, and ammonia (NH3), whose smell you recognize in strong home cleaning products. Carbon monoxide is particularly abundant in interstellar space and is the primary tool that astronomers use to study giant molecular clouds. Unfortunately, the most abundant molecule, H2, is particularly difficult to observe directly because in most giant molecular clouds, it is too cold to emit even at radio wavelengths. CO, which tends to be present wherever H2 is found, is a much better emitter and is often used by astronomers to trace molecular hydrogen.

Explain why nearest galaxies are not in motion away from us.

Closer galaxies are affected more by gravity than the expansion of the universe

protogalactic cloud

Cloud with mass equal to that of a galaxy

What are nebulae?

Clouds of gas and dust

What are clumps in a molecular cloud? Find the mass range of clumps.

Clumps are denser areas of the molecular. These are usually where stars begin to form. Usually have a mass 50-500 solar masses

What is the local group?

Cluster of galaxies that the milky way is part of

What are stellar Clusters?

Clusters of stars

Find the speed of collapse during the iron crisis

Collapses at speeds at 70000 km/s. Happens in tenths of seconds.

Find the rate of galaxy collisions in the universe's history.

Collisions have been decling as the universe expands

Which parameters of exoplanets can we determine with the radial velocity technique?

Composition, period, mass and orbital radius

Which parameters of exoplanets can we determine with the radial velocity and transit together?

Composition, period, size ratio, mass and orbital radius

Find the difference between the core of a planet and the core of a cloud.

Composition- the core of a planet is usually made of heavier metals. Temperature - not super hot (unlike planet core) until they start collapsing.

What causes a contracting protostar to spin-up?

Conservation of Angular momentum. As the radius decreases, the velocity increases

In what case, the universe expansion will be 1) constant, 2)decelerating, 3) accelerating.

Constant: no change in age Decelerating: overestimate age Accelerating: underestimate age

What happens under a sunspot?

Cool material from the sunspot flows downward, and material surrounding the sunspot is pulled inward, carrying magnetic field with it and thus maintaining the strong field that is necessary to form a sunspot. As the new material enters the sunspot region, it too cools, becomes denser, and sinks, thus setting up a self-perpetuating cycle that can last for weeks. The downward-flowing cool material acts as a kind of plug that block the upward flow of hot material, which is then diverted sideways and eventually reaches the solar surface in the region around the sunspot. This outward flow of hot material accounts for the paradox that we described in The Sun: A Garden-Variety Star—namely, that the Sun emits slightly more energy when more of its surface is covered by cool sunspots.

Order of Sun's layers Inside to outside

Core: 20% of solar interior& hottest part of the sun Radiative Zone: starts from 25% through the solar interior all the way to 70% of the way through Convection Zone: outermost layer of the solar interior Photosphere: can't see through it Chromosphere: red streak Transition region Corona

Where does solar wind predominantly come from?

Coronal holes, where gas can stream away from the sun into space, unhindered by magnetic fields.

What can effect space weather?

Coronal mass ejections (CME), coronal holes, and solar flares

In addition to gas and dust, a third class of particles, noteworthy for the high speeds with which they travel, is found in interstellar space. What are they?

Cosmic rays were discovered in 1911 by an Austrian physicist, Victor Hess, who flew simple instruments aboard balloons and showed that high-speed particles arrive at Earth from space (Figure 20.17). The term "cosmic ray" is misleading, implying it might be like a ray of light, but we are stuck with the name. They are definitely particles and have nearly the same composition as ordinary interstellar gas. Their behavior, however, is radically different from the gas we have discussed so far.

Find why we were not sure about the existence of other galaxies for a very long time

Couldn't accurately measure large distances and decipher what we were seeing

Poor and Rich clusters

Defined as poor or rich depending on how many galaxies they have. Rich can have thousands or tens of thousands of galaxies

open universe

Density is less than critical density so the universe expands forever

closed universe

Density will become greater than critical density and gravity will cause big crunch

How can we measure the surface temperature of a star?

Determined by examining the spectra. You can also approximate it as a blackbody using Wien's Law.

How can we measure the chemical composition of a star?

Determined by looking at the stellar spectra

What did the Universe look like when it was 3 minute old?

Deuterium, helium, and lithium had formed was much cooler

Find the observing evidence that supports the idea that spirals seem to form mostly "bottom-up."

Different ages fpr all the stars in all the sections of the galaxy. Since not all at the same time must have come from seperate parts

Spiral arms

Differential galactic rotation is why spiral arms form as the stars and other interstellar matter trails behind in their orbits

Direct Imaging Method

Direct imaging uses infrared wavelengths to observe planets. This works because at infrared wavelengths a star like the Sun is only 100 times brighter than Jupiter, compared to a billion (109) times brighter at visual wavelengths. This method works for planets that are very far from their stars, so an orbit might take hundreds or thousands of years for a planet discovered by this method. Astronomers have to verify that the planet and the star move together through space to prove that the planet orbits the star since observing an entire orbit will take so long. This method does not allow astronomers to measure the mass of a planet directly, but they can use the spectrum and brightness to get information about its surface temperature and diameter.

Vesto M. Slipher

Discovered that Andromeda and Triangulum Galaxies and M81 were approaching the milky way and all other galaxies were moving away. Used redshift observation to make discovery

Edwin Hubble:

Discovered that other galaxies existed, classified them on the basis of their shapes, found a pattern to their motion.

Describe the size, density, and temperature of the neutral hydrogen clouds in the Milky Way galaxy.

Disk that is 300 lightyears thick (super flat). Temperature around 100K

Discuss the disk radiation difference between disk with formed planets and without formed planets.

Disks with planets have rings that are bright. Radiation is related to ring thickness.

The electrons that are captured by the hydrogen nuclei cascade down through the various energy levels of the hydrogen atoms on their way to the lowest level, or ground state. During each transition downward, they give up energy in the form of what?

During each transition downward, they give up energy in the form of light. The process of converting ultraviolet radiation into visible light is called fluorescence. Interstellar gas contains other elements besides hydrogen. Many of them are also ionized in the vicinity of hot stars; they then capture electrons and emit light, just as hydrogen does, allowing them to be observed by astronomers. But generally, the red hydrogen line is the strongest, and that is why H II regions look red.

What is cosmic dust?

Dust from space. Made up of small particles. Sometimes fall to earth

What are protoplanetary disks made of?

Dust, ice, gas, metals

What is the interstellar medium?

Dust, radiation, etc. between stars

Thanks to their small sizes and low temperatures, interstellar grains radiate most of their energy at infrared to microwave frequencies, with wavelengths of tens to hundreds of microns. How does this relate to earth?

Earth's atmosphere is opaque to radiation at these wavelengths, so emission by interstellar dust is best measured from space. Observations from above Earth's atmosphere show that dust clouds are present throughout the plane of the Milky Way

What is the Copernicus principle?

Earth/humanity is not in any special place in the universe

What is the most common type of false positives that can mimic an exoplanet transit?

Eclipsing binaries

What is the difference of gravity between general relativity and Newton's gravity?

Einstein's is curved spacetime whereas Newton is action-at-a-distance.

What is General Relativity?

Einstein's theory of gravity. Includes curved spacetime and the equivalence principle and other things

How can we measure the mass of a star?

Either by observing the mass of stars in a binary system from their orbits, or estimating the stars mass based on its other characteristics and known star characteristics

No supernova explosion has been observable in our Milky way since the invention of the telescope. Why?

Either we are unlucky, or interstellar dust blocks the light from the explosions

What will happen when the gravity of a white dwarf is strong enough to break electron degeneracy?

Electron capture. The electrons will combine with protons to produce neutrons and neutrinos

What are degenerate electrons?

Electrons in a super dense system that can move around a little but not much because if they did, they would violate the Pauli exclusion principle.

Find the pieces of observing evidence that support the "bottom-up" elliptical galaxy formation model.

Elliptical galaxies have different ages

What are the differences between spectral lines from giants and dwarfs?

Giants have lower pressure in the photosphere and therefore have narrower absorption lines

Hubbles' Law & Constant

Equation used to calculate the distance of any galaxy. Using the velocity the galaxy is moving velocity = hubble's constant x distance hubble's constant = 22km/s per million years

What are cores in a clump?

Even denser regions in the dense clumps. These are form the center of stars

Which is hotter, the chromosphere or the photosphere?

Even though it is farther from the core, the chromosphere is hotter

What is a technique that involves making a light curve of an eclipsing binary, a graph that plots how the brightness changes with time. (Let us consider a hypothetical binary system in which the stars are very different in size, and to make life easy, we will assume that the orbit is viewed exactly edge-on.)

Even though we cannot see the two stars separately in such a system, the light curve can tell us what is happening. When the smaller star just starts to pass behind the larger star (a point we call first contact), the brightness begins to drop. The eclipse becomes total (the smaller star is completely hidden) at the point called second contact. At the end of the total eclipse (third contact), the smaller star begins to emerge. When the smaller star has reached last contact, the eclipse is completely over. During the time interval between the first and second contacts, the smaller star has moved a distance equal to its own diameter. During the time interval from the first to third contacts, the smaller star has moved a distance equal to the diameter of the larger star. If the spectral lines of both stars are visible in the spectrum of the binary, then the speed of the smaller star with respect to the larger one can be measured from the Doppler shift. But knowing the speed with which the smaller star is moving and how long it took to cover some distance can tell the span of that distance—in this case, the diameters of the stars. The speed multiplied by the time interval from the first to second contact gives the diameter of the smaller star. We multiply the speed by the time between the first and third contacts to get the diameter of the larger star.

How often do Supernovae occur in the Milky Way?

Every 25 to 100 years

How can you determine the stellar temperature?

Examining the stellar spectra, examining the peak wavelength, comparing it to other stars on the HR diagram, and by looking at the luminosity of the star and using the Stefan-Boltzmann law.

Why is it difficult to detect exoplanets?

Exoplanets are usually very small, especially compared to the host star

What is the solar nebular hypothesis? What is the evidence supporting the hypothesis?

Formation of the solar system from a nebula. We can date everything in our system to roughly the same age, which means they came from the same material. We can also observe star formations in other nebulae.

What is a Supernova?

Explosion after star death

Find the location, the amount of heavy elements, and the age of Pop III stars.

Extremely far away almost no heavy elements. Part of the first generation of stars

Quasar Luminosity

Extremely luminous far their large distance. Quasars also emit energy at X-ray and ultraviolet wavelengths, and some are radio sources as well. When all their radiation is added together, some QSOs have total luminosities as large as a hundred trillion Suns. Luminosity of a quasar can vary over time scales.

Find Newton's Theory of Gravity.

F=GmM/r^2

For a main-sequence star, where is its energy from?

Fusion of hydrogen into helium

What are false positives? And false negatives?

False positive would maybe be when you believe there's an exoplanet due to shifts but aren't actually there. False positive could be seeing a dip in the sunlight that could mean there's another planet but is really an eclipsing binary.

What is the Pauli exclusion principle?

Fermions are not able to occupy the same quantum state as another electron

What's first, second, third, and fourth contact?

First: initial contact; Second: fully within; Third: reaches the edge; Fourth: completely clears

What's the thick disk of the Milky Way Galaxy?

Flat central plane 3000ly above and below the thin disk.

What's the thin disk of the Milky Way Galaxy?

Flat central plane, 100,000 ly diameter & 2000 ly thick

How can you measure the size of a star?

For eclipsing binaries, can be deduced from light curve, if they're single stars and they happen to get covered by the moon then their angular diameter can be found

What's the problem with using Hubble's law to measure the distance to a galaxy?

For galaxies far away hubble's law does not account for the universes acceleration

Find the difference between a galactic merger and a galactic cannibalism

Galactic merger is when both galaxies are the same size. Galactic cannibalism is when one is much larger

Find the life story of SN 1987A (From star formation to supernova)

Formed about 10 million years with about 20 solar masses. Spectral type O with 60000 times the sun's luminosity. Lived on the main sequence for 90% of its life. Eventually swelled to a red giant and emitted 100000 times the luminosity of the sun burning helium. Then it became a blue supergiant once the helium was exhausted and fused heavier elements. Finally, it collapsed and rebounded.

Find mechanisms to form the seed black hole of a supermassive black hole.

Formed nearby large amounds of matter

Describe two main types of elliptical galaxy formation models.

Formed top-down which is a gas cloud collapsing in on itself or bottom-up which is small galaxies colliding into each other into an ellipse

How does the sun rotate?

From west to east, using differential rotation, as it is faster at the equator, and slower as you go farther north or south from there. Rotation period is 25 days at the equator, 28 days at latitude 40, and 36 days at latitude 80

How do stars make energy during the main-sequence stage?

Fusing hydrogen into helium

Fusion vs Fission

Fusion is sun combining particles to make Helium 4 and getting energy from that Fission is scientists breaking apart nuclei to make atomic bombs

Galaxies age

Galaxies age can be determined by their spectra. Galaxies with blue stars are younger than galaxies with red stars. This can also give us the age of the universe by looking as far as possible to see light that originated 13 billion year ago which shows us early galaxies forming whose light is just now reaching us.

Dark Matter in Clusters of Galaxies

Galaxies in clusters orbit the cluster's center of mass. The galaxies themselves don't have enough mass to keep then together so dark matter must be present. Dark matter can also be detected by gravitational lensing where spacetime curves in regions where gravity is strong. Can also be detected by taking images of light of x-rays. The gas in the clusters gives off x-ray wavelengths and the more mass the faster and hotter the gas which makes the x-rays brighter. The math shows that their is invisble mass in the cluster causing that

Irregular Galaxies

Galaxies that do not have the regular shapes. Have lower masses and luminosities than spiral galaxies. Appear disorganized like my desk. Undergoing intense star formation activity. Contain a mix of population I&II stars

Describe the properties of spiral galaxies.

Galaxy with spiral arms and central bulge

What observing properties of hot Jupiter challenged the traditional planet formation model?

Gas Giants were thought to only form far from its star, where it was cold enough to collect the large number of particles.

Why were hot Jupiters so surprising?

Gas Giants were thought to only form far from its star, where it was cold enough to collect the large number of particles.

Why couldn't it be the interstellar gas that reddens distant stars and not the dust?

Gas wouldn't scatter the light as much, it would absorb the energy from the light and re-emit it as a photon

The relationship between dark matter and luminous matter in the universe.

Generally found together where there is no ordinary matter there will probably be no dark matter, where matter clusters then dark matter will also cluster

What does it mean if we detected heavy elements in a galaxy very far away from us?

Generations of stars have lived and died in that galaxy before we observed it

Find the element difference between globular clusters and open clusters. Explain it.

Globular clusters have older, cooler stars than cannot fuse heavier metals. Open clusters have younger, hotter stars than can fuse heavier elements. So stars in an open cluster tend to have a higher metallicity.

End of the Quizlet

Go take a break

What is the principle of equivalence?

Gravitational and inertial forces are indistinguishable

Why does the contraction of a star produce energy?

Gravitational potential energy produces thermal energy. Mass and temperature

What is gravitational lensing?

Gravity bends the path of light because light always travels on a geodesic curve. This means you can see one object located behind another

Find how tidal force tears apart an object close to it.

Gravity is stronger the closer it is to an object and will tear it apart as it pulls the object towards itself

Find the brightness-luminosity-distance relation.

Greater Luminosity, greater brightness, but greater distance, lower brightness, distance vs. brightness is the inverse square law D^2 = L/(4piB) D = distance L = luminosity B = apparent brightness

What are galaxy clusters?

Groups of galaxies kept together by gravity

Find the relation between the mass and the mass-to-light ratio of a star.

High mass stars have low ratios & low mass stars have higher ratios

Why is the luminosity of a spiral galaxy related to its rotational velocity?

Higher rotation means higher mass means higher luminosity.

What did the Universe look like when it was 0.01s old?

Hot, dense, opaque

What determines the amount of energy emitted by a black hole.

How much material is available and size of the black hole

What are Population III stars?

Hypothetical Massive stars

What is the cosmological constant?

Hypthetical constant that explains the universe expanding and contracting

The most widely used system of star classification divides stars of a given spectral class into six categories called luminosity classes. These luminosity classes are denoted by Roman numbers as follows:

Ia: Brightest supergiants Ib: Less luminous supergiants II: Bright giants III: Giants IV: Subgiants (intermediate between giants and main-sequence stars) V: Main-sequence stars

What's interstellar dust made of?

Ice, and small particles

What's the oscillating theory of the Universe?

Idea that the big bang causes expansion from a single point and then the big crunch causes retraction into a single point causing the big bang again in a cycle

We can also use the Doppler effect to measure how fast a star rotates. How is this done?

If an object is rotating, then one of its sides is approaching us while the other is receding (unless its axis of rotation happens to be pointed exactly toward us). This is clearly the case for the Sun or a planet; we can observe the light from either the approaching or receding edge of these nearby objects and directly measure the Doppler shifts that arise from the rotation.

starburst

If either galaxy contains interstellar matter, the collision can compress the gas and trigger an increase in the rate at which stars are being formed. Up to a factor of 100

What is the approximate spectral class of a star with: The strongest lines are those of ionized helium.

If in the spectrum of star the strongest lines are those of ionized helium. These characteristics correspond to temperature above 30,000K. So, this temperature range corresponds to spectral type O. Example of such type of star is Lacertae

Why does the main sequence have most of stars on it?

If most of star's lives spend most of their time in the main sequence, its a higher probability that we will observe most stars there. When stars burn hydrogen into helium, which is most of their composition, there are in the main sequence.

Without dark energy, will the Universe expand forever?

If the densitiy was still not higher than the critical density then yes but slower

deuterium density

If the density were relatively high, nearly all the deuterium would have been converted into helium through interactions with protons, just as it is in stars. If the density were relatively low, then the universe would have expanded and thinned out rapidly enough that some deuterium would have survived. The abundance of deuterium today tells us the estimate of the current density of the universe

Explain how we know that the Sun's energy is not supplied either by chemical burning, as in fires here on Earth, or by gravitational contraction (shrinking).

If the sun's energy was supplied by chemical burning, there would be some residue and such high temperatures of the sun could not be caused by chemical burning. If the sun's energy source was gravity contracting, the layers of the sun would fall inwards and cause the sun's size to shrink, and according to kelvin and helmholtz, the contraction rate of the sun would about 40 meters per year, and if this was true, the sun would be super tiny after the billions of years that it has already lived.

Universe accelerating or decelerating

If the universe were decelerating, we would expect the far-away supernovae to be brighter than expected. The slowing down would have kept them closer to us. Instead, they were fainter, which at first seemed to make no sense. Suppose, instead, that the universe is accelerating. If the universe is expanding faster now than it was billions of years ago, our motion away from the distant supernovae has sped up since the explosion occurred, sweeping us farther away from them. The light of the explosion has to travel a greater distance to reach us than if the expansion rate were constant. The farther the light travels, the fainter it appears. So the answer is the expansion of the universe is accelerating

A milestone in exoplanet detection history was the Hubble Space Telescope survey for transiting planets in the globular cluster 47 Tucanae. Despite observing ≈34,000 stars nearly continuously for 8.3 days, with a precision high enough to detect giant planets, the authors did not find any planets. Find the possible explanations.

If they could only detect gas giants that are probably pretty close to the stars, and the stars are older as they are in a globular cluster, there is a possibility that most of the stars that had a planet had already expanded into red giants, capturing the gas giants that the HST could detect.

How can we calculate how far a star is from us?

If we know how luminous the star really is and see how dim it looks, the difference allows us to calculate its distance.

How can a star be cool, and yet very luminous?

Larger stars would have higher luminosity, but not necessarily have higher temperatures

How can you measure the size of a star by using the moon across the star's disk?

If you measure the time it takes for the moon to completely cover the star, you have angular diameter, which will give you actual diameter if you know the distance

How is the H-R diagram formed?

Imagine a cluster of stars forming from a cloud of interstellar "raw material" whose chemical composition is similar to the Sun's. In such a cloud, all the clumps of gas and dust that become stars begin with the same chemical composition and differ from one another only in mass. Now suppose that we compute a model of each of these stars for the time at which it becomes stable and derives its energy from nuclear reactions, but before it has time to alter its composition appreciably as a result of these reactions. The models calculated for these stars allow us to determine their luminosities, temperatures, and sizes. If we plot the results from the models—one point for each model star—on the H-R diagram, we get something that looks just like the main sequence we saw for real stars.

What happened in 2009?

In 2009, astronomers discovered ultra-cool brown dwarfs with temperatures of 500-600 K. These objects exhibited absorption lines due to ammonia (NH3), which are not seen in T dwarfs. A new spectral class, Y, was created for these objects. As of 2021, over 50 brown dwarfs belonging to spectral class Y have been discovered, some with temperatures comparable to that of the human body (about 300 K).

Why does the technique that involves making a light curve of an eclipsing binary not work?

In actuality, the situation with eclipsing binaries is often a bit more complicated: orbits are generally not seen exactly edge-on, and the light from each star may be only partially blocked by the other. Furthermore, binary star orbits, just like the orbits of the planets, are ellipses, not circles. However, all these effects can be sorted out from very careful measurements of the light curve.

In the first step of the sun's nuclear reaction process, a positron flies out toward space, but another particle is also emitted from the first step alongside the positron. What is it and what does it do?

In addition to the positron, the fusion of two hydrogen atoms to form deuterium results in the emission of a neutrino. Because neutrinos interact so little with ordinary matter, those produced by fusion reactions near the center of the Sun travel directly to the Sun's surface and then out into space, in all directions. Neutrinos move at nearly the speed of light, and they escape the Sun about two seconds after they are created.

What is the helium flash? What causes the helium flash?

In low mass stars, the entire core ignites at once when the triple-alpha process begins

Compare the density of the sun, red dwarfs, white dwarfs, and supergiants

In order of descending density: white dwarfs, red dwarfs, the sun, supergiants

In hotter stars, another set of reactions, called the carbon-nitrogen-oxygen (CNO) cycle, accomplishes the same net result as the proton-proton chain. What happens?

In the CNO cycle, carbon and hydrogen nuclei collide to initiate a series of reactions that form nitrogen, oxygen, and ultimately, helium. The nitrogen and oxygen nuclei do not survive but interact to form carbon again. Therefore, the outcome is the same as in the proton-proton chain: four hydrogen atoms disappear, and in their place, a single helium atom is created. The CNO cycle plays only a minor role in the Sun but is the main source of energy for stars with masses greater than about the mass of the Sun.

Hydrogen, for example, is by far the most abundant element in most stars. However, lines of hydrogen are not seen in the spectra of the hottest and the coolest stars. Why is this so?

In the atmospheres of the hottest stars, hydrogen atoms are completely ionized. Because the electron and the proton are separated, ionized hydrogen cannot produce absorption lines. In the atmospheres of the coolest stars, hydrogen atoms have their electrons attached and can switch energy levels to produce lines. However, practically all of the hydrogen atoms are in the lowest energy state (unexcited) in these stars and thus can absorb only those photons able to lift an electron from that first energy level to a higher level. Photons with enough energy to do this lie in the ultraviolet part of the electromagnetic spectrum, and there are very few ultraviolet photons in the radiation from a cool star. What this means is that if you observe the spectrum of a very hot or very cool star with a typical telescope on the surface of Earth, the most common element in that star, hydrogen, will show very weak spectral lines or none at all.

Why are spiral galaxies more likely to be found in poor clusters or on the edges of rich clusters?

In the center of clusters there are more collisions which turn spirals into ellipticals so they are found away from the center in rich clusters and in poor clusters where there are a lack of collisions

hot dark matter

In the early universe, if dark matter particles easily moved fast and far compared to the lumps and bumps of ordinary matter that eventually became galaxies and larger structures. In that case, smaller lumps and bumps would be smeared out by the particle motions, meaning fewer small galaxies would get made.

What is the proton-proton chain?

It is the three step nuclear reaction process in the sun that we have studied

What is the approximate spectral class of a star with: Balmer lines of hydrogen that are very strong; some lines of ionized metals are present

In the spectrum Balmer lines of hydrogen are very strong. So star can be a B star, an A star or a F star. Whereas some lines of ionized metals are present then it must be a type A. These characteristics correspond to temperature range approximately from 7500-10,000K. Examples of such type of star are Sirius and Vega

Grand Unified Theories, GUTS

In these theories, the strong, weak, and electromagnetic forces are not three independent forces but instead are different manifestations or aspects of what is, in fact, a single force. The theories predict that at high enough temperatures, there would be only one force. At lower temperatures like the current universe this single force has changed into three different forces.

In a single day since the outburst, the supernova soared in brightness by a factor of about 1000. Find the change in the magnitude.

Increases in magnitude by 7.54

In what ways is a ground-based telescope superior/inferior to a space-based telescope?

Inferior: Atmospheric disturbance, Light pollution | Superior: cheaper, require less complex technology, access to any Earth-based skilled technician

In which wavelength, we can observe molecular clouds? Why?

Infrared. According to Wien's law, the low temperature corresponds to a longer wavelength

Brown dwarfs are very difficult to observe because they are extremely faint and cool, and they put out most of their light in the infrared part of the spectrum. It was only after the construction of very large telescopes, like the Keck telescopes in Hawaii, and the development of very sensitive infrared detectors, that the search for brown dwarfs succeeded. How were they initially treated?

Initially, brown dwarfs were given spectral classes like M10+ or "much cooler than M9," but so many are now known that it is possible to begin assigning spectral types. The hottest brown dwarfs are given types L0-L9 (temperatures in the range 2400-1300 K), whereas still cooler (1300-700 K) objects are given types T0-T9 (see Figure 17.8). In class L brown dwarfs, the lines of titanium oxide, which are strong in M stars, have disappeared. This is because the L dwarfs are so cool that atoms and molecules can gather together into dust particles in their atmospheres; the titanium is locked up in the dust grains rather than being available to form molecules of titanium oxide. Lines of steam (hot water vapor) are present, along with lines of carbon monoxide and neutral sodium, potassium, cesium, and rubidium. Methane (CH4) lines are strong in class-T brown dwarfs, as methane exists in the atmosphere of the giant planets in our own solar system.

Why didn't a supernova fade away at the same rate?

Initially, it is all energy from the explosion until about day 40. After that, it is still bright because of the radioactive elements present

What causes interstellar extinction?

Interstellar dust

What causes interstellar reddening?

Interstellar dust and the fact it scatters blue light more

What's interstellar extinction?

Interstellar extinction is when light from a star is scattered or absorbed by interstellar dust appears dimmer

Why is the fusion of silicon into iron the last step in the sequence of nonexplosive element production?

Iron is the most stable and has the highest binding energy. It would lose energy fusing iron

Find why some elements (oxygen, carbon, and iron) are common, and others are quite rare (gold, silver, and uranium).

Iron is the most stable element, so the heavier elements are only formed in supernovae and other high-energy phenomena.

What is the difference between "isotropic" and "homogeneous"?

Is direction vs location

What is agn (active galactic nucleus) feedback? How agn affect star formation in a galaxy?

Is how AGN changes the color, shape, & composition of a galaxy. Prevents star formation by charging up and breaking up interstellar matter

Describe the properties of the local group.

Is over 3 million ly wide, 60 galaxies most of which are dwarf galaxies, mass about 4*10^12 solar masses

How did Hubble conclude that the universe is isotropic and homogeneous?

Isotropic by seeing that there are a similar amount of galaxies in all directions and homogeneous by seeing that they had similar densities regardless of distance

Find the total mass of gas and dust in the Milky Way Galaxy.

It accounts for about 15%

Why is it surprising that the Tully-Fisher relation works?

It assumes there is no dark matter although there's a lot of it

Why is a red giant larger than it was on its main-sequence phase?

It begins to produce more energy, so the star briefly produces more energy

A more massive star has more fuel. Why is its lifetime shorter?

It burns the fuel faster

Why can we only see a fraction of the pulsars in the Milky Way?

It can be blocked by material and the beam might not hit Earth.

For a low mass star, why is there no further step of fusion after the triple-alpha process?

It can't get hot enough to fuse heavier metals

What do magnetic loops offer a natural explanation of?

It explains why the leading and trailing sunspots in an active region have opposite polarity. The leading sunspot coincides with one end of the loop and the trailing spot with the other end. The forces produced by the magnetic field resist the motions of the bubbling columns of rising hot gases. Since these columns carry most of the heat from inside the Sun to the surface by means of convection, and strong magnetic fields inhibit this convection, the surface of the Sun is allowed to cool. As a result, these regions are seen as darker, cooler sunspots.

Where do heavy elements come from?

It fuses up to iron and then all of the other heavy elements are formed in other highly energetic events, namely supernovae

Where is the solar dynamo located?

It is either located in the convection zone or in the interface layer between the convection zone and the radiative zone below it. As the magnetic fields fro the sun's dynamo interact, they break, reconnect, and rise through the sun's surface

what is the binding energy greatest for?

It is greatest for atoms with a mass near that of the iron nucleus. With that said, Iron is the most stable element since it gives up the most energy when it forms

Why is the moon approximately the same angular size as the Sun? Is this a coincidence?

It is much closer. This is a coincidence

Is it possible to have a black hole in our solar system? Why? Or Why not?

It is possible to have unstable black holes (created in like labs) that don't last long. But we would have probably detected a stable black hole that was larger

Starting from the core of the Sun and going outward, the temperature decreases. Yet, above the photosphere, the temperature increases. How can this be?

It may be caused by plasma jets. The plasma which is below the convection zone moves upward when it gets heated and shoots out from the photosphere. As it gets heated, it moves upwards to the chromosphere and when it is at the corona, it loses its heat to the outer space and as it gets cooled down, it sinks back to the bottom of the convection zone

What will happen for a low-mass star after the helium in the core was used up?

It no longer can fuse elements so the core compresses and can then form a supernovae

Find the reason for pulsar spin down.

It radiates energy so the rotation speed decreases

For a low mass star, what will happen after all helium in the core gets used up.

It shrinks again and gets hotter, and keeps fusing a small amount of heavier metals.

Explain the evolutionary track of the Sun on the HR diagram.

It will continue up the main sequence until its turnoff, at which point it goes up to a red giant, then loops around to the left and down to a white dwarf.

Why was it surprising to find hot gas in an elliptical galaxy?

It's odd because the stars are old and have low rates of star formation

Is our solar system stable?

It's stable for a short time scale (compared to human lifetime). However, long term it is not stable.

What is ultra-hot Interstellar gas? What is the reason for this extreme temperature?

It's ultra-hot interstellar gas. It has a temperature up to a million kelvin and is heated by supernovae explosions. It emits x-ray and UV radiation.

How can we see the corona without a total solar eclipse?

Its brighter parts can now be photographed with a special instrument—a coronagraph—that removes the Sun's glare from the image with an occulting disk (a circular piece of material held so it is just in front of the Sun).

Describe the structure and temperature distribution of a massive star when an iron core is formed.

Its structured like an onion with different burning shells around the core, and the temperature decreases with radius

Why are energetic electrons and other particles near a supermassive black hole ejected into jets, and often into two oppositely directed jets, rather than in all directions?

Jets are perpendicular to the accretion disk because path otherwise is blocked by the accretion disk

What are hot Jupiters? What are super-earths? What are mini-Neptunes?

Jupiter-like planets orbiting close to the star, large earth like planets, mini Neptunes: planets 3-4 times the mass of earth

How can we measure the mass of the black hole in the center of the milky way galaxy?

Keplers third law

What is up with L, T, and Y types?

L types are cooler than type M stars. They have temperature in range from 1300 to 2400 K. These are mainly red in color. The spectrum contains mainly metal hydride lines and alkali metal lines. Examples of L type is Teide 1. T types are cooler than type L stars. They have temperature in range from 700 to 1300 K. The color of T types is magenta. The spectrum contains methane lines because of low temperature. Example of T type is Giliese 229B Y types are further cooler than type T. They have temperature less than 700K. The spectru contains ammonia lines and in infrared part because of low temperature. Examples of Y type are WISE 1828+2650

Theories of Supermassive black hole Sagittarius A's origin

Large cloud of gas near center of Milky Way collapsed into black hole. An initial single massive star may have exploded into a black hole and then dense clusters of stars collapsed into it.

Find the relation between the stellar mass and its evolution timescale of a star.

Larger stars tend to have shorter lifetimes because they quickly burn up their fuel supply

cosmic microwave background (CMB)

Leftover radiation from the big bang. Comes from all direction (isotropic)

What does the beam of pulsar consist of?

Light and radiated particles

Describe the line broadening of an elliptical galaxy.

Line broadening squared is proportional to galactic mass

What is the approximate spectral class of a star with: Lines of ionized calcium are the strongest in the spectrum; hydrogen lines show only moderate strength; lines of neutral and metals are present.

Lines of ionized calcium are the strongest in the spectrum, so, it can be an F star, a G star, or a K star, but if the spectrum also contains lines of neutral and metals, then it can be either a G star or a K star. Whereas if it contains hydrogen lines with only moderate strength, then it is a G star. Examples of such type of star are the sun and Capella

Supermassive black hole Sagittarius A

Located at the center of the galaxy

Find the location, the amount of heavy elements, and the age of Pop II stars.

Located in halo. Extremely low metallicity, 11-13 billion years old

Why is long-wavelength radiation transmitted through the Galaxy more efficiently than short-wavelength radiation

Long-wavelengths aren't scattered as easily because it collides with less objects

Why can only a lower limit to the rate of stellar rotation be determined from line broadening rather than the actual rotation rate?

Look at chegg chapter 17 problem 25

How can we determine the star's initial mass to reach the Chandrasekhar limit when it runs out of fuel?

Look at young, open clusters.

How can we find binary systems? What's the challenge?

Looking at motions of stars through spectroscopy, doppler shift in spectra, challenge is two stars can look like they're close in the sky but are actually super far away

How can we measure the radial velocity of a star?

Looking at the doppler shift of the spectra

(ACTUALLY LOOK UP THE FIGURE IN 17.3) To see how spectral classification works, let's use Figure 17.5. Suppose you have a spectrum in which the hydrogen lines are about half as strong as those seen in an A star. What could the star be? (ACTUALLY LOOK UP THE FIGURE IN 17.3)

Looking at the lines in our figure, you see that the star could be either a B star or a G star. But if the spectrum also contains helium lines, then it is a B star, whereas if it contains lines of ionized iron and other metals, it must be a G star.

Why is the Universe itself a kind of time machine?

Looking farther away allows us to look at light that originated long ago

What are open Clusters?

Loose group of stars

What are red dwarfs?

Low mass stars that are cooler and not very luminous, and just able to start fusion. Masses of 0.08-0.6 solar masses

Low-mass red M dwarfs make up about what percent of all stars?

Low-mass red M dwarfs make up about 70% of all stars and dominate the census of stars within 10 parsecs (33 light-years) of the Sun. For example, a recent survey of the solar neighborhood counted 357 stars and brown dwarfs within 10 parsecs, and 248 of these are red dwarfs. Yet, if you wanted to see an M dwarf with your naked eye, you would be out of luck. These stars only produce a fraction of the Sun's light, and nearly all of them require a telescope to be detected.

Luminous matter vs Invisible Matter

Luminous matter is any material that can be detected via electromagnetic radiation. Invisible Matter needs to be detected by gravitational changes

Find the pieces of observing evidence that support the "top-down" elliptical galaxy formation model.

Luminous quasars found early on in the galaxies life

What is the magnitude equation?

Mabs=Mapp-5*log(d)+5

How are auroras made?

Magnetic field lines come into earth at the north and south magnetic poles. Charged particles are accelerated by the solar wind can follow the field down into our atmosphere. As the particles strike molecules of air, they case them to glow, producing beautiful curtains of light called Auroras

When astronomers find an exciting event, how do they know what was going on before the event?

Make predictions based on models and other observations

How did we know the temperature at the center of a star?

Make predictions from mass. Also we can make a prediction based on the temperature needed for fusion to take place

Describe the Sloan Digital Sky Survey.

Mapping project that madea a 3D model of the universe

What determines how hot a star's central regions get?

Mass

What is mass? How can we measure the mass of an object?

Mass is how much an object resists acceleration

Explain how the mass and radius of white dwarfs are related.

Mass is inversely related to radius

What determines how high the pressure in the core must be?

Mass, temperature, and radiation pressure

What determines the rate of hydrogen fusion in a star?

Mass, temperature, pressure. More massive stars fuse faster

How does stellar rotation affect stellar shape?

Massive rotating bodies oblate at their equator (they bulge)

Find the difference of post-main-sequence evolution between massive stars and low mass stars.

Massive stars continue to burn and move up and right whereas less massive stars run out of fuel and move down and right

Why can we see the ring around supernova 1987A?

Material expelled by the star

Where is the energy from when nearby material falls into black holes? How does the energy convert?

Material falling into black hole heats up the accretion disk and converts potential gravitational energy into heat&kinetic energy

Black hole energy production

Matter spirals in toward the spinning black hole and forms an accretion disk of material around it. As the material spirals ever closer to the black hole, it accelerates and becomes compressed, heating up to temperatures of millions of degrees.

What does "homogeneous" mean?

Means the same everywhere

How can we measure the distance of a galaxy?

Measure redshift using hubble's law or using standard bulbs

How can we determine how rapidly material moves in spiral galaxies?

Measuring line broadening

How can we estimate the mass of a spiral galaxy beyond its visible edge?

Measuring stars&clusters orbiting at the edge of the galaxy

How can we measure the size of a star?

Measuring the angular diameter of a star as it transits the moon

How can we measure the size of quasars?

Measuring the variation of the light

What is the future fate of the milky way?

Merge with Andromeda galaxy

What process can change the shapes of a galaxy?

Mergers,Collisions, Cannibilism, taking in or releasing interstellar mass

What is gyrochronology?

Method of estimating the age of the sun from its spin rate

What is an optical double?

Mizar and Alcor form an optical double—a pair of stars that appear close together in the sky but do not orbit each other. Through a telescope, as Riccioli discovered in 1650, Mizar can be seen to have another, closer companion that does orbit it; Mizar is thus a visual binary. The two components that make up this visual binary, known as Mizar A and Mizar B, are both spectroscopic binaries. So, Mizar is really a quadruple system of stars.

How do most brown dwarfs start out?

Most brown dwarfs start out with atmospheric temperatures and spectra like those of true stars with spectral classes of M6.5 and later, even though the brown dwarfs are not hot and dense enough in their interiors to fuse hydrogen. In fact, the spectra of brown dwarfs and true stars are so similar from spectral types late M through L that it is not possible to distinguish the two types of objects based on spectra alone. An independent measure of mass is required to determine whether a specific object is a brown dwarf or a very low mass star. Since brown dwarfs cool steadily throughout their lifetimes, the spectral type of a given brown dwarf changes with time over a billion years or more from late M through L, T, and Y spectral types.

The breakthrough in measuring distances to remote parts of our Galaxy, and to other galaxies as well, came from the study of variable stars. Most stars are constant with respect to what value?

Most stars are constant in their luminosity, at least to within a percent or two. Like the Sun, they generate a steady flow of energy from their interiors. However, some stars are seen to vary in brightness and, for this reason, are called variable stars. Many such stars vary on a regular cycle, like the flashing bulbs that decorate stores and homes during the winter holidays.

Why is a galaxy's mass-to-light ratio generally greater than 1?

Most stars are low mass stars

Find the composition of a neutron star.

Mostly neutrons

What do different stars in the same cluster have in common?

Mutual gravitational attraction, similar composition, similar origin, and similar space velocity

How does time change near a black hole?

Near a black hole, time would appear to move slower

What's the Tarantula Nebula?

Nebula within an irregular galaxy, is an HII region in the Large Magellanic Cloud, very luminous

Neutrinos produced in the core of the Sun carry energy to its exterior. Is the mechanism for this energy transport conduction, convection, or radiation?

Neutrinos produced in the sun's core carry energy to the sun's exterior. The energy is carried away from the sun's core by radiation. This is because neutrinos are extremely small and light weight so they do not interfere with other matter such as protons, so they make it to the surface in just 2 seconds. The photons and neutrinos both travel to the surface of the sun by the mode of radiation. Conduction does not take place in the sun since it is not a solid, however, convection does transport about 30% of the energy in the sun, whereas 70% of the sun's energy is transported by radiation

Find the typical size of a neutron star and a typical size of a white dwarf.

Neutron stars are about 20 km in diameter and white dwarfs are slightly bigger than Earth

What are degenerate neutrons?

Neutrons that cannot move much because if they did, they would violate the Pauli Exclusion principle

Why is the sky blue?

Nitrogen in the atmosphere scatters blue light more than red light, so the sky appears blue.

Suppose all the galaxies are moving away from us. Does this mean we are the center of the Universe? Why not?

No as everything is moving away from everything else so from any observer they are the center of the universe

Elliptical galaxies

No spiral arms. Consist almost entirely of old stars and have shapes that are spheres or ellipsoids. Made of population II stars. Can range from giants with large mass and luminosity to dwarfs that went unnoticed for years

Are galaxies increasing their sizes as the Universe expands?

No they are held together by gravity

What is a singularity?

No volume and infinite density. Where spacetime stops existing

Do you think that nuclear fusion takes place in the atmospheres of stars? Why or why not?

No, nuclear fusion does not take place in the atmospheres of stars because there doesn't exist high enough temperatures, densities or pressures to fuse two atoms

Does stellar color depend on the distance of the object to Earth?

No; colors → temp/wavelength(unless star is fast)

Is the Hubble constant a constant? What does it mean if the Hubble constant never changes?

Not constant because the rate of expansion of the universe is increasing if it never changed then the rate of expansion would be constant

Why can the observed deuterium not be produced by the fusion in stars?

Not hot enough

Temperature when CMB was emitted

Not perfectly uniform temperature. The early universe must have had tiny density fluctuations from which such structures could evolve. Regions of higher-than-average density would have attracted additional matter and eventually grown into the galaxies and clusters that we see today. It turns out that these denser regions would appear to us to be colder spots, that is, they would have lower-than-average temperatures.

Where do neutrinos come from?

Nuclear fusion and cosmic rays

Find Newton's laws of motion.

Object at rest stays at rest, object in motion stays in motion unless acted upon by an outside force. F=ma. And lastly, Every action has an equal and opposite reaction.

Differential galactic rotation

Objects farther from the center take longer to complete an orbit around the Galaxy than do those closer to the center.

Invisible Matter & Kepler's 3rd Law

Objects farther out from the center of the galaxy should move slower but they don't. This is because these objects are orbiting another source of gravity

To help astronomers remember this crazy order of letters, Cannon created a mnemonic, what is it?

Oh Boy, An F Grade Kills Me Too Young (for OBAFGKM & TY)

Find the difference in HR diagrams between young clusters and old clusters. Explain how the H-R diagram of a star cluster can be related to the cluster's age.

Older clusters would be farther along the HR diagram than younger clusters. This means you would expect more red giants in older clusters and less O-type stars

What can be seen when sunspots are observed in pairs, or in groups containing two principal spots?

One of the spots usually has the magnetic polarity of a north0seeking magnetic pole, and the other has the opposite polarity, and during a given cycle, the leading spots of pairs ( or leading principle spots of groups) in the Northern hemisphere all tend to have the same polarity, whereas those in the Southern Hemisphere all tend to have the opposite polarity.

What could dark energy be

One possibility is that it is the cosmological constant, which is an energy associated with the vacuum of empty space itself. Quantum mechanics tells us that the source of this vacuum energy might be tiny elementary particles that flicker in and out of existence everywhere throughout the universe.

How much fraction of the matter incorporated into stars will go back into interstellar space?

Only about ⅓ of the mass incorporated into stars returns to the ISM after their lifetime

What is multi-messenger astronomy?

Only being able to detect an object indirectly using light, gravitational waves, and other forms of detection

The conventional planet formation theory is based on centuries of observation of our solar system itself. Why is this a problem?

Only observing our solar system limits us to just our eight planets, whereas other systems can have other properties.

Find the reason why stars in an open cluster can not remain together for a long time. Is this a problem for a globular cluster or a stellar association?

Open clusters and stellar associations are both very loosely bound together, so they are easily torn from each other. Globular clusters have a much larger gravitational association and are difficult to tear apart.

Why didn't our Jupiter become a hot Jupiter?

Our Jupiter did not migrate inwards after formation.

Why is the sun yellow?

Our Sun's surface temperature is about 6000 K; its peak wavelength color is a slightly greenish-yellow. In space, the Sun would look white, shining with about equal amounts of reddish and bluish wavelengths of light. It looks somewhat yellow as seen from Earth's surface because our planet's nitrogen molecules scatter some of the shorter (i.e., blue) wavelengths out of the beams of sunlight that reach us, leaving more long wavelength light behind. This also explains why the sky is blue: the blue sky is sunlight scattered by Earth's atmosphere.

Find the name of the first discovered pulsar

PSR B1919+21

What is the most common type of planet in our galaxy?

Planets with 1-3 times radius of Earth, super earths

Review all the techniques that we learned to measure distance.

Parallax, HR diagram estimation, variable stars, radar astronomy.

What is the structure of the cosmic distance ladder?

Parallaxes are the foundation of all stellar distance estimates, spectroscopic methods use nearby stars to calibrate their H-R diagrams, and RR Lyrae and cepheid distance estimates are grounded in H-R diagram distance estimates (and even in a parallax measurement to a nearby cepheid, Delta Cephei).

What is the Hayashi track?

Pattern that infant stars less than three solar masses follow on the HR diagram. Shows that contracting protostars must follow an almost vertical path downward on the HR diagram

Critical density of the universe equation

Pcrict = (3H^2)/(8piG) Pcrit = critical density H = hubble constant G = unversal constant of gravity

What properties can you get for variable stars from their light curves?

Period and average luminosity

How are Cepheid variables used to measure distance?

Period during when the star is fluctuating, we can observe its luminosity. We can use the magnitude equation to get the distance.

Galactic Year

Period of suns revolution around the center of the galaxy. 225 million years

How can we use cepheids to measure the celestial distances?

Period to Luminosity relation. Then find aboslute magnitude which when compared to apparent brightness can give distance

What is the difference between photometry, Astrometry, spectroscopy?

Photometry deals with visible light, astrometry deals with positions and movement of stars using their light, and spectroscopy deals with analyzing the light of individual stars

Plages are found near sunspots, but they can appear even in areas without sunspots. Why is this?

Plages are found near sun spots, but they can also outlive them. this is because the solar activity also depends upon the sun's magnetic field. Plages are caused by excess heating of the solar chromosphere above the facular regions. Faculae are bright spots produced by concentrations of magnetic field lines near the sun spots. the sunspots may remain for days and the faculae may remain for months even after the sunspot is gone from that location. This may cause plages to appear on the surface of the sun, even without sun spots

Through photographs that use filters that only transmit light at the emission lines of hydrogen and calcium that are produced in the hot gases of the chromosphere, we can take pictures of bright clouds in the chromosphere that has higher temperature and density that their surroundings called what?

Plages, which contain all of the elements in the sun

What happens during inflation

Prior and during inflation all parts of the universe are close together and can exchange information so universe homegenizes to the same temperature and then inflation occurs to now parts of the universe are beyond other's horizon. Explains why density of universe is equal to critical density. This is because the universe is so large that there is no curvature similar to how from our perspective on land the earth feels flat. A universe that has higher or lower density than the critical density would have marked curvature

What are protoplanetary disks? What are debris disks?

Protoplanetary disks and debris disks are clouds of dust, ice, and material around a star. Protoplanetary disks accrete the dust into protoplanets and have eventually form planets.

Astronomers have observed that the RR Lyrae stars occurring in any particular cluster all have what?

RR Lyrae stars occurring in any particular cluster all have about the same apparent brightness. Since stars in a cluster are all at approximately the same distance, it follows that RR Lyrae variables must all have nearly the same intrinsic luminosity, which turns out to be about 50 times the luminosity of the sun. In this sense, RR Lyrae stars are a little bit like standard light bulbs and can also be used to obtain distances, particularly within our Galaxy.

List several standard bulbs for distance measurement.

RR Lyrae, type Ia supernovae, planetary nebulae, cephids

How can we measure the eccentricity of a planet? Why do eccentric orbits challenge the conventional planetary formation model?

Radial velocity method. Circular orbits are more stable so thought to be the norm.

What are pulsars?

Rapid regularly rotating neutron stars

For a binary system, or a planet-star system, what can the radial velocity method measure?

Rate of change of distance between the objects. Their orbital distance. How further or closer they are moving in our line of sight.

What is the most common type of stars in the universe?

Red dwarf stars

Why is a red giant more luminous than it was on its main-sequence phase?

Red giants produce more energy in the core by burning the hydrogen shell than by the fusion of hydrogen in the core. Also, it appears brighter because its larger

What are H II regions?

Red regions that Ionize Hydrogen. Red because of Balmer lines

What is the central bulge？

Region of high density in center of galaxy

What are planetary nebulae? Find the typical size of a planetary nebula.

Regions of hot ionized gas that is ejected from a dying star that are roughly one light-year in diameter

What factors determine transit depth?

Relative size of stars, and distance between the object, and orbital plane with respect to Earth

What is the zero-age main sequence?

Represents the left side of the main-sequence on the HR diagram. When a star begins to fuse hydrogen in its core and stops contracting

Where is the energy of a white dwarf from?

Residual thermal energy

What are gravitational waves?

Ripples in spacetime caused by accelerating gravitational masses.

Are the amount of ionized atoms proportional or inversely proportional to size?

Second, more atoms are ionized in a giant star than in a star like the Sun with the same temperature. The ionization of atoms in a star's outer layers is caused mainly by photons, and the amount of energy carried by photons is determined by temperature. But how long atoms stay ionized depends in part on pressure. Compared with what happens in the Sun (with its relatively dense photosphere), ionized atoms in a giant star's photosphere are less likely to pass close enough to electrons to interact and combine with one or more of them, thereby becoming neutral again. Ionized atoms, as we discussed earlier, have different spectra from atoms that are neutral.

Voids

Separating the filaments and sheets in a supercluster

What causes the gaps in Saturn's rings?

Shepard moons

What happens to the positrons that flies away in the first step of the sun's nuclear reaction process?

Since it is antimatter, this positron will instantly collide with a nearby electron, and both will be annihilated, producing electromagnetic energy in the form of gamma-ray photons. This gamma ray, which has been created in the center of the Sun, finds itself in a world crammed full of fast-moving nuclei and electrons. The gamma ray collides with particles of matter and transfers its energy to one of them. The particle later emits another gamma-ray photon, but often the emitted photon has a bit less energy than the one that was absorbed. Such interactions happen to gamma rays again and again and again as they make their way slowly toward the outer layers of the Sun, so by the time they reach the Sun's surface, most of the photons have given up enough energy to be ordinary light—and they are the sunlight we see coming from our star.

What is an eclipsing binary star system?

Some binary stars are lined up in such a way that, when viewed from Earth, each star passes in front of the other during every revolution. When one star blocks the light of the other, preventing it from reaching Earth, the luminosity of the system decreases, and astronomers say that an eclipse has occurred.

What is the angular diameter of an object?

The angle that it takes to cover the diameter of the object as it appears in the sky

The nearest star visible without a telescope from most of the United States is the brightest appearing of all the stars, is what?

Sirius, which has a distance of a little more than 8 light-years. It too is a binary system, composed of a faint white dwarf orbiting a bluish-white, main-sequence star. It is an interesting coincidence of numbers that light reaches us from the Sun in about 8 minutes and from the next brightest star in the sky in about 8 years.

Which parameters of exoplanets can we determine with the transit technique?

Size ratio, orbital period

What are Dwarf ellipticals?

Small elliptical galaxies with faint luminosities

If you need to design a transit survey, do you prefer a large telescope (usually a small field of view) or a small telescope (usually a large field of view)? Will you monitor one patch of sky for a long time or different patches of sky, and each patch for a short time?

Small telescope with one path at a time. Study the star to see if it could qualify, if not, move on to the next.

Is Hubble constant in the early universe larger than it is right now? Why or why not?

Smaller because we have found that the universe is accelerating

How can a star be hot, and yet very dim?

Smaller stars may have lower luminosity

Find the difference between galaxies in the distant past, and what they are today.

Smaller, less structure , and more galaxies in the past today galaxies are larger with structure

How can the prominences, which are so big and 'float' in the corona, stay gravitationally attached to the Sun while flares can escape?

Solar flares are the violent explosions on the sun's surface and due to the energy released in the explosion, it escapes the sun's photosphere. However, sometimes prominences release large amounts of material. racing through corona, when it reaches about 5x10^4 km or more above the sun's atmosphere. Since they are large in mass and held by the sun's strong magnetic field, it is not easy for them to escape the photosphere, in fact, most of the matter drains back down. But solar flares are energies released due to magnetic reconnection which leads to acceleration of charged particles. The sudden release of energy from reconnection is the main cause of particle acceleration. The unconnected magnetic field along with the particles are violent released causing solar flares to escape the sun's photosphere

If matter falls toward a black hole, find the velocity when it is near the event horizon of the black hole.

Some large fraction of the speed of light

The classic HR diagram plots the stellar luminosities vs. their effective temperatures. Find other form HR diagrams.

Some plot absolute magnitude vs. temperature, etc. Just different ways of graphing the same reality

Radio Jets

Some quasars can have long jets that glow with radio waves, light, and sometimes even X-rays, and that extend beyond the limits of the parent galaxy. Form perpendicular to the disk

What is the "getting a birth kick"?

Some supernovae don't happen equally on each side, so the neutron star is ejected from the supernovae to one side.

standard bulbs

Sources of light that have near constant luminosity for every star of its type. Unfortunately both stars and galaxies have wide range of luminosities. However type 1 supernovas, white dwarf explosions, have all near the same luminosity and are useful for determining distance as their light gets dimmer over distance

What is the intergalactic medium?

Space between galaxies

How do we know what the nebulae are (clusters in the Milky way or distant Galaxies)?

Spectra for compositions and doppler effect for distance

How can we measure the orbital speed of stars in a spiral galaxy?

Spectral broadening of the galaxy due to the doppler shift

What are RR Lyrae variables? Describe their property (spectral class, period, etc.).

Spectral class A→ F with a mass half of our sun, their periods range from a few hours to a few days, they have nearly the same luminosity to our sun.

How do we estimate the mass of an elliptical galaxy?

Spectral line broadening indicates range of speeds & keplers third law

What is the spectral type and luminosity type of a star? How can we determine them?

Spectral type, what color and temperature the star; luminosity is how bright the star is. We can determine them by estimating the temperature and color. We can estimate its luminosity by plotting it on the HR diagram because we have its estimate on its spectral class (from its peak wavelength).

Which measurement is easier and more precise? The speed of a galaxy or the distance of a galaxy?

Speed of galaxy because speed is measured and then distance is calculated from that number

What's the stellar halo of the Milky Way Galaxy?

Spherical region containing stars that encompasses galaxy around 150,000 ly from center, less dense than disks

Describe the properties of Sc galaxies

Spiral galaxies that are loosely bound. Have luminous stars and emissions nebula.

Describe the properties of Sb galaxies

Spiral galaxies that are looser bound.

Describe the properties of Sa galaxies

Spiral galaxies that are tightly wound. Faint arms.

What are lenticular galaxies?

Spiral galaxies where the spiral arms have begun to dissipate

What are barred spiral galaxies?

Spiral galaxies with a bar of stars in the center

What are normal spiral galaxies?

Spiral galaxies without a bar in the center

Find the difference between spiral galaxies and elliptical galaxies.

Spiral have disk&halo and are usually younger Elliptical have spheroidal distribution no arms or bulges generally older

Describe ISM distribution in different types of galaxies.

Spirals have lots of ISM in thin disk and bulge, elliptical galaxies & irregular galaxies have less

Explain the impact of supernovae on life.

Spreads out all of the important elements for life, such as nitrogen, carbon, oxygen, etc. Also produces heavier elements

What is the Toomre Q?

Stability criteria for dirrerentially roating disks

Star X has lines of ionized helium in its spectrum, and star Y has bands of titanium oxide. Which is hotter? Why? The spectrum of star Z shows lines of ionized helium and also molecular bands of titanium oxide. What is strange about this spectrum? Can you suggest an explanation?

Star X has lines of ionized helium in its spectrum, so, it is a type O star. O stars have temperature 40,000 K. So, temperature of a star X over 40,000K Star Y has bands of titanium oxide in its spectrum, so, it is a type M star. M stars have temperature of about 2000K. So, temperature of star Y about 2000K. Clearly star X is hotter than star Y The spectrum of star Z shows lines of ionized helium and also molecular bands of titanium oxide because it is a binary star. This is composed of a hot and cold star. The hot star is responsible for lines of ionized helium in the spectrum, and the cold star is responsible for bands of titanium oxide in its spectrum

Find why even the youngest stars in the Small Magellanic cloud are deficient in heavy elements?

Star formation here is slow so there are not many supernovas that can produce a lot of metals to enrich other stars

What's the most luminous type of galaxies?

Starburst galaxies

What is apparent brightness?

Stars are democratic in how they produce radiation; they emit the same amount of energy in every direction in space. Consequently, only a minuscule fraction of the energy given off by a star actually reaches an observer on Earth. We call the amount of a star's energy that reaches a given area (say, one square meter) each second here on Earth its apparent brightness.

Why does hydrogen fusion not change a star's total mass appreciably during the star's main sequence phase?

Stars are super massive. 0.7% of the hydrogen is used

population II Star

Stars in the halo and globular clusters. Found throughout galaxy. Some have eccentric elliptical orbits that go above the galactic disk into the halo. Consist of old stars. Have less abundance of heavier elements

What are Population II stars?

Stars located in halo and globular clusters

What are Population I stars?

Stars located in the disk/spiral arms

What are white dwarfs?

Stars smaller than 1.4 solar masses that are very hot but not very luminous. They are no longer able to fuse heavier elements, and don't collapse because of the electron degeneracy

What are brown dwarfs?

Stars that are similar in radius to Jupiter but much more massive. Not able to fuse hydrogen

What are pulsating variable stars?

Stars that change brightness periodically by pulsating in size, like a cepheid variable.

What are variable stars? List its classification.

Stars which have varying brightness on a regular cycle. They can either be extrinsic (like pulsating and eruptive stars) or intrinsic (like eclipsing or rotating variables)

How do we measure the rotational speed of a star that is very very very far away?

Stars, however, are so far away that they all appear as unresolved points. The best we can do is to analyze the light from the entire star at once. Due to the Doppler effect, the lines in the light that come from the side of the star rotating toward us are shifted to shorter wavelengths and the lines in the light from the opposite edge of the star are shifted to longer wavelengths. You can think of each spectral line that we observe as the sum or composite of spectral lines originating from different speeds with respect to us. Each point on the star has its own Doppler shift, so the absorption line we see from the whole star is actually much wider than it would be if the star were not rotating. If a star is rotating rapidly, there will be a greater spread of Doppler shifts and all its spectral lines should be quite broad. In fact, astronomers call this effect line broadening, and the amount of broadening can tell us the speed at which the star rotates

What is the main sequence of an H-R diagram

Stars, like people, are not distributed over the diagram at random, as they would be if they exhibited all combinations of luminosity and temperature. Instead, we see that the stars cluster into certain parts of the H-R diagram. The great majority are aligned along a narrow sequence running from the upper left (hot, highly luminous) to the lower right (cool, less luminous). This band of points is called the main sequence. It represents a relationship between temperature and luminosity that is followed by most stars. We can summarize this relationship by saying that hotter stars are more luminous than cooler ones.

Where is the light emitted by galaxies from?

Stars, quasars, hot gases

Describe the accretion process of planet formation.

Start small particles that lump together. Once they reach 10 cm in size, they must grow to small planetesimals or their orbit will decay eventually falling into their star. Once they reach 100 m across, they will rapidly grow until about 100 km across. These objects will collect smaller ones, the biggest of which become planets.

Stellar convection occurs when?

Stellar convection occurs as currents of hot gas flow up and down through the star (Figure 16.12). Such currents travel at moderate speeds and do not upset the overall stability of the star. They don't even result in a net transfer of mass either inward or outward because, as hot material rises, cool material falls and replaces it. This results in a convective circulation of rising and falling cells as seen in Figure 16.12. In much the same way, heat from a fireplace can stir up air currents in a room, some rising and some falling, without driving any air into or out the room. Convection currents carry heat very efficiently outward through a star. In the Sun, convection turns out to be important in the central regions and near the surface.

What are molecular clouds?

Stellar nursery. Cold clouds with actual molecules that form (mostly H II)

Explain why the first generation of star formations triggered the formation of additional stars? Do all stars form by this process?

Stellar winds disrupt the molecular clouds and push away hot gas so that cooler, denser gas can condense and form into stars. No

Harlow Shapley:

Studied RR Lyrae variable stars in globular clusters. Compared known intrinsic luminosity of the stars to how bright they appeared. Then calculated distance. Discovered our galaxies true size and our actual location

According to studies of stellar spectra, what are most stars made of?

Studies of stellar spectra have shown that hydrogen makes up about three-quarters of the mass of most stars. Helium is the second-most abundant element, making up almost a quarter of a star's mass. Together, hydrogen and helium make up from 96 to 99% of the mass; in some stars, they amount to more than 99.9%. Among the 4% or less of "heavy elements," oxygen, carbon, neon, iron, nitrogen, silicon, magnesium, and sulfur are among the most abundant. Generally, but not invariably, the elements of lower atomic weight are more abundant than those of higher atomic weight.

If we can't directly detect the changes over time in individual galaxies because they happen too slowly, how then can we ever understand those changes and the origins of galaxies?

Studying galaxies at different distances to compare a galaxy that's light from billions ago

What did the Universe consist of when it was 0.01s old?

Subatomic particles and radiation

Some dense clouds of dust are close to luminous stars and scatter enough starlight to become visible. Such a cloud of dust, illuminated by starlight, is called what?

Such a cloud of dust, illuminated by starlight, is called a reflection nebula, since the light we see is starlight reflected off the grains of dust. One of the best-known examples is the nebulosity around each of the brightest stars in the Pleiades cluster (see Figure 20.1). The dust grains are small, and such small particles turn out to scatter light with blue wavelengths more efficiently than light at red wavelengths. A reflection nebula, therefore, usually appears bluer than its illuminating star

What are Gamma Ray Bursts?

Sudden releases of gamma rays

What are neutron stars?

Super dense stars that have collapsed and overcome the electron degeneracy pressure so the atoms experience electron capture, and thus the star is supported only by neutron degeneracy.

Find the typical size of a giant and a supergiant. Compare them to the planetary orbits in our solar system.

Supergiants are usually between 50-300 solar radii, but can be larger than 1000 solar radii. Slightly smaller for giants. Giants are less than Earth's orbit and Supergiants are larger than Earth's orbit

Find what powers quasars.

Supermassiev blackhole at the center pulls in accretion disk which the density heats it up

What are supergiants?

Supermassive stars that are really hot and bright and also don't live long

Where is interstellar dust made?

Supernovae

Where are the elements heavier than iron from?

Supernovae and other high energy events (possibly neutron star collisions)

What is the frequency of supernovae in our Milky Way Galaxy?

Supernovae occur about every 100 years in the Milky Way

What caused the Local Bubble to form?

Supernovae. Hot gas from winds drove away the cooler, denser gas

Age of the universe

T0 = d/v T0 = age of universe d= distance v= rate of which a galaxy is receding from milky way When Hubble law is plugged in for v a new equation is found T0 = d/v = d/(H*d) = 1/H Universe age about 14 billion years old

what are the most active prominences?

Sure prominences which move up to 1300 km/s

hot accretion disk

Surrounds a black hole. Consists of gas and dust that swirl around the black whole before falling in

What is a T Tauri star?

T Tauri stars are variable stars that are less than 10 million years old. They are pre-main sequence and follow the Hayashi track

What does "isotropic" mean?

Taking a measurement in any direction results in the same result

If you had a telescope with a small field of view, how can you get the entire picture of the sky?

Taking many pictures and putting them together

How do we know that ultra-hot interstellar gas is a million degrees at least?

Telescopes launched above Earth's atmosphere obtained ultraviolet spectra that contained interstellar lines produced by oxygen atoms that have been ionized five times. To strip five electrons from their orbits around an oxygen nucleus requires a lot of energy. Subsequent observations with orbiting X-ray telescopes revealed that the Galaxy is filled with numerous bubbles of X-ray-emitting gas. To emit X-rays, and to contain oxygen atoms that have been ionized five times, gas must be heated to temperatures of a million degrees or more.

The interstellar medium is not static. List three properties of the interstellar medium that may change.

Temperature (gas clouds), density (also gas clouds), and ionization of molecules

How can we detect the cold Neutral Hydrogen Clouds?

The 21 cm line

How did astronomers detect the cold Neutral Hydrogen Clouds for the first time?

The 21 cm line was first detected by a telescope at Harvard that was able to detect such a big wavelength

An interesting property of brown dwarfs is that they are all about the same radius as Jupiter, regardless of their masses. Amazingly, this covers a range of masses from about 13 to 80 times the mass of Jupiter (MJ). This can make distinguishing a low-mass brown dwarf from a high-mass planet very difficult. So, what is the difference between a low-mass brown dwarf and a high-mass planet?

The International Astronomical Union considers the distinctive feature to be deuterium fusion. Although brown dwarfs do not sustain regular (proton-proton) hydrogen fusion, they are capable of fusing deuterium (a rare form of hydrogen with one proton and one neutron in its nucleus). The fusion of deuterium can happen at a lower temperature than the fusion of hydrogen. If an object has enough mass to fuse deuterium (about 13 MJ or 0.012 MSun), it is a brown dwarf. Objects with less than 13 MJ do not fuse deuterium and are usually considered planets.

What is the Local Bubble?

The Local Bubble is a low density cavity in the ISM with density of about 0.01 atoms/cm^3. It is around our solar system in the Orion arm of the Milky way

Compare the age of the sun and the age of the earth.

The Sun is about 100 million years older than the earth.

What is hydrostatic equilibrium?

The Sun maintains its stability in the following way. If the internal pressure in such a star were not great enough to balance the weight of its outer parts, the star would collapse somewhat, contracting and building up the pressure inside. On the other hand, if the pressure were greater than the weight of the overlying layers, the star would expand, thus decreasing the internal pressure. Expansion would stop, and equilibrium would again be reached when the pressure at every internal point equaled the weight of the stellar layers above that point. An analogy is an inflated balloon, which will expand or contract until an equilibrium is reached between the pressure of the air inside and outside.

What is the maximum mass of a stable neutron star ("Chandrasekhar limit" for neutron stars)?

The Tolman-Oppenheimer-Volkoff limit is around 2.1 solar masses for cold, non-rotating neutron stars. Some created in supernovae have masses up to 3 solar masses

Find another technique for measuring galactic distances.

The Tully Fisher relation, which determines the rotation speed of galaxies from the 21cm line of cold hydrogen, allowing an estimate on luminosity and mass of a galaxy, which we can then compare to what we observe to determine distances to the galaxy.

Since like charges repel via the electrical force, the closer we get two nuclei to each other, the more they repel. It's true that if we can get them within "striking distance" of the nuclear force, they will then come together with a much stronger attraction. But that striking distance is very tiny, about the size of a nucleus. How can we get nuclei close enough to participate in fusion?

The answer turns out to be heat—tremendous heat—which speeds the protons up enough to overcome the electrical forces that try to keep protons apart. Inside the Sun, as we saw, the most common element is hydrogen, whose nucleus contains only a single proton. Two protons can fuse only in regions where the temperature is greater than about 12 million K, and the speed of the protons average around 1000 kilometers per second or more. So, even the sun can't get that many protons to combine very often at all, so most of it's protons haven't been involved in fusion reactions

What's the Olbers' paradox?

The arguement that every line of sight should end up on a star if the universe is infinite so the sky should be very bright but it's actually dark

What is the center of mass?

The average location of all the mass in a system

Where is the center of mass located in a binary star system?

The barycenter, point where both stars orbit about

What is nucleosynthesis?

The building of heavier elements from lighter ones by nuclear fusion

Where can we find a supermassive black hole?

The center of the galaxy

Why wasn't the SN1054 reported in European history?

The church suppressed the information

If we find an O-type star in a stellar cluster, what does this mean?

The cluster is young and possibly still forming stars because the O-type stars don't live long

Describe the model picture of interstellar grains (core+mantle)

The core is made of dense iron/ carbon silicates and the mantle is made of ice. It looks sorta like a cell

Within what fraction of the Sun's radius does practically all of the Sun's luminosity originate?

The core is the region that extends from the center of the sun to about 25% of its radius outwards. The core generates 99% of the fusion power of the sun. It is inside the core that the fusion of hydrogen to form helium takes place and energy is generated. The fusion process stops entirely after about 30% of the radius and is concentrated only in the core. Therefore, maximum part of the sun's energy comes from the central region which is the core.

For a solar mass star, what will happen after the red giant phase?

The core of the star shrinks because there is not enough energy being produced in the hydrogen shell. Once the core shrinks and gets hot enough, it begins fusing helium.

For a low mass star, what will happen after all hydrogen in the core gets used up.

The core shrinks and gets hotter, making a hot hydrogen burning shell around it. It starts to fuse helium

What is the critical density of the Universe?

The critical densitity is the density that needs to be passed by the universe for gravity to overcome dark matter and cause the big crunch

What's the cause of donut-shaped disks?

The debris disk collapsing in a star in the center, and other dust is accreted outwards. Planets can form early and sweep out gaps in the disk.

What is the accretion disk around a black hole?

The disk of infalling gas around a black hole that gets hot and glows very bright

How can we measure the mass of black holes in other galaxies?

The doppler effect measures the radial velocity of the gas around the black hole. Then kepler's third law is used to find the mass

How do atoms make molecules on the surface of interstellar dust?

The dust grains are so large compared to atoms, that the atoms can find spaces to form molecules. The presence of the dust shields the molecules from UV and cosmic rays that would break them up.

What is the event horizon of a black hole?

The edge of where the escape velocity is the speed of light around a black hole

Quasar energy

The energy being emitted is being produced by a hot accretion disk

How can you create matter at the beginning of the Universe?

The energy converted to matter as photons collided with each other in the extreme heat

dark energy

The entire universe contains some mysterious energy that pushes spacetime apart, taking galaxies and the larger structures made of galaxies along with it. Observations show that dark energy becomes more and more important relative to gravity as the universe ages.

Big Bang

The explosion of that concentrated universe at the beginning of time

The spectrum of the Sun has hundreds of strong lines of nonionized iron but only a few, very weak lines of helium. A star of spectral type B has very strong lines of helium but very weak iron lines. Do these differences mean that the Sun contains more iron and less helium than the B star? Explain.

The factor which determines the type of spectral absorption lines is temperature. Lines of each element are changed with the temperature. Strong lines of nonionized iron but only a few very weak lines of helium in the spectrum of the sun give the temperature of the sun. However, these do not give any clues as to their abundance in the sun. Strong lines of helium but very weak iron lines in the spectrum of type B star give the idea that temperature of that star is more than the sun. In that star, iron is mostly in an ionized state, so, that star shows only weak iron lines. So, star A of spectral type B has very strong lines of helium but very weak iron then the sun gives an idea about the temperature of the star. But these differences do not mean that the sun contains more iron and less helium than the B star

How fast can a neutron star spin? Why can it spin so quickly?

The fastest spinning pulsar is about 716 rpm. Spins so quickly because of conservation of angular momentum

What is Gravity?

The force that pulls you down towards the center of the planet

How does gravity act at a distance?

The further the distance, the more potential energy you have. You might also weigh less

Where is the energy of a protostar from before the nuclear reaction begins?

The gas is dense and contracting, which heats the core (like Jupiter)

Dark Matter Halo

The gravitational influence on distance star clusters and other dwarf galaxies

What will happen for a star when its hydrogen in the core is used up?

The gravity overcomes the internal pressure and it collapses. Some stars actually expand as they begin to fuse heavier elements

Hydrogen is the most abundant element in all types of stars. But why do both the coolest stars and the hottest stars show weak Hydrogen lines?

The hydrogen in coolers stars need UV light to be put into a higher energy level, and these coolers stars lack enough UV light.

Where are Balmer lines strongest?

The hydrogen lines in the visible part of the spectrum (called Balmer lines) are strongest in stars with intermediate temperatures—not too hot and not too cold. Calculations show that the optimum temperature for producing visible hydrogen lines is about 10,000 K. At this temperature, an appreciable number of hydrogen atoms are excited to the second energy level. They can then absorb additional photons, rise to still-higher levels of excitation, and produce a dark absorption line. Similarly, every other chemical element, in each of its possible stages of ionization, has a characteristic temperature at which it is most effective in producing absorption lines in any particular part of the spectrum.

cosmological principle

The idea that the universe is the same everywhere is called

The importance of cepheid variables lies in what?

The importance of cepheid variables lies in the fact that their periods and average luminosities turn out to be directly related. The longer the period (the longer the star takes to vary), the greater the luminosity. This period-luminosity relation was a remarkable discovery, one for which astronomers still (pardon the expression) thank their lucky stars. The period of such a star is easy to measure: a good telescope and a good clock are all you need. Once you have the period, the relationship (which can be put into precise mathematical terms) will give you the luminosity of the star.

The brightest stars, those that were traditionally referred to as first-magnitude stars, actually turned out (when measured accurately) not to be identical in brightness. For example, the brightest star in the sky, Sirius, sends us about 10 times as much light as the average first-magnitude star. How does the magnitude scale work?

The important fact to remember when using magnitude is that the system goes backward: the larger the magnitude, the fainter the object you are observing.

What determines a star's main sequence lifetime?

The initial mass of the star

First step of sun's nuclear reactions

The initial step required to form one helium nucleus from four hydrogen nuclei is shown in Figure 16.6. At the high temperatures inside the Sun's core, two protons combine to make a deuterium nucleus, which is an isotope (or version) of hydrogen that contains one proton and one neutron. In effect, one of the original protons has been converted into a neutron in the fusion reaction. Electric charge has to be conserved in nuclear reactions, and it is conserved in this one. A positron (antimatter electron) emerges from the reaction and carries away the positive charge originally associated with one of the protons.

Describe two steps of Jupiter formation (core formation, run-away gas accretion).

The inner rocky core forms, and if it's 10 earth masses, it will be able to collect hydrogen, then undergoing a fast mass acquisition of gas.

What is the baryon cycle?

The interstellar medium forms stars and then they go back into interstellar medium in the form of supernovae

List the sources of Gamma-ray emissions.

The jets are emitting gamma radiation because the material is very energized

When this dust accumulates in a single location, the result is a dark cloud where ultraviolet starlight is blocked and molecules can survive. The largest of these structures are created through what?

The largest of these structures are created where gravity pulls interstellar gas together to form giant molecular clouds, structures as massive as a million times the mass of the Sun. Within these, most of the interstellar hydrogen has formed the molecule H2 (molecular hydrogen). Other, more complex molecules are also present in much smaller quantities.

Palkia and Dialga

The legendary pokemon of space and time.

Find the difference between a black hole in the center of a galaxy and those are not in the center of a galaxy.

The location. Also the center of the galaxy ones are usually supermassive black holes whereas those not at the center are smaller.

What determines the upper and lower mass limit of a main-sequence star?

The lower limit is the mass at which the stars can fuse hydrogen, and the upper limit is about 100 solar masses, and is the point when a star produces so much energy it cannot hold itself together

Is the earth's rotation axis aligned with its magnetic axis? Why?

The magnetic poles are aligned with the core of the Earth, which isn't always aligned with the rotation axis

What is the main reason that the spectra of all stars are not identical? Explain.

The main reason for this is because each element has a particular set of absorption lines. For example, hydrogen is the main constituent of most stars. In the hottest stars, hydrogen is fully ionized due to high temperature of the star, ionized hydrogen cannot produce absorption lines. In the coldest stars, most of hydrogen atoms are in the lowest energy state. We need photons from the ultraviolet region to lift an electron from the first energy level to a higher level but there are very few ultraviolet photons in the radiation from a cool star. At the intermediate temperatures (around 9000K) photons have enough energy to lift the electron to a higher energy level. So, the hydrogen lines are the strongest in the visible part of the star.

What is the main-sequence turnoff, and explain how the main-sequence turnoff of a cluster reveals its age.

The main sequence turnoff is where main sequence stars leave the main sequence. This would be more common in older clusters because the main sequence stars would have had time to go through the main sequence and begin to turn into dwarfs or red giants

A disk of gas and dust appears to be an essential part of star formation. Observations show that nearly all very young protostars have disks and that the disks range in size from 10 to 1000 AU. (For comparison, the average diameter of the orbit of Pluto, which can be considered the rough size of our own planetary system, is 80 AU, whereas the outer diameter of the Kuiper belt of smaller icy bodies is about 100 AU.) The mass contained in these disks is typically what percent of the mass of our sun?

The mass contained in these disks is typically 1-10% of the mass of our own Sun, which is more than the mass of all the planets in our solar system put together. Such observations already demonstrate that a large fraction of stars begin their lives with enough material in the right place to form a planetary system.

What's the metallicity of a star? How can it be a negative value?

The metallicity measures the abundance of elements heavier than helium. It can be negative because it's probably measure on a log scale

What do certain locations on the H-R diagram tell us?

The model stars with the largest masses are the hottest and most luminous, and they are located at the upper left of the diagram. The least-massive model stars are the coolest and least luminous, and they are placed at the lower right of the plot. The other model stars all lie along a line running diagonally across the diagram. In other words, the main sequence turns out to be a sequence of stellar masses.

What is angular momentum?

The momentum related to going around an object. L=iw=mvr

What do measurements of the number of neutrinos emitted by the Sun tell us about conditions deep in the solar interior?

The number of neutrinos coming from the sun tells us about the nuclear fission in the solar interior. The more number of neutrinos tells us that the rate of fusion reaction is more, and less neutrinos says that the sun's fuel is low and it may explode anytime soon.

Evolution of Quasars

The number of quasars have decreased as time goes on. Pattern is similar to decrease of star formation. Reasoning for this is that black holes consume the material needed to make the accretion disk or that material is blown away in jets

Find the relationship between the number of stars and stellar mass.

The number of stars is inversely proportional to the mass, with red dwarfs being most common

Why can infalling material to a black hole produce x-ray emission?

The object is moving very fast and hits objects that are in the way. It heats up a lot and produces x rays

Find how age and heavier-element abundance are correlated.

The older the star the less metallicity is has

Why do we believe the collapse is a speedy process?

The oldest of the population 1 stars in about the same age as the youngest halo star

A number of stars, however, lie above the main sequence on the H-R diagram, in the upper-right region, where stars have low temperature and high luminosity. How can a star be at once cool, meaning each square meter on the star does not put out all that much energy, and yet very luminous?

The only way is for the star to be enormous—to have so many square meters on its surface that the total energy output is still large. These stars must be giants or supergiants, the stars of huge diameter we discussed earlier.

What would you say to a friend who made this statement, "The visible-light spectrum of the Sun shows weak hydrogen lines and strong calcium lines. The Sun must therefore contain more calcium than hydrogen."?

The optimum temperature for producing spectral lines is about 10,000K. But, the temperature of su is about 5,800K. The hydrogen atoms not excited to higher levels. At this temperature an appreciable number of calcium excited to a higher level. The mean of weak hydrogen lines and strong calcium lines in the spectrum of the sun at that temperature is that ostly atoms of hydrogen are in ground and most of calcium atoms are able to produce absorption lines. So, his argument is wrong and strong lines of calcium in the sun signify that it is a G type star.

How do we know that the protogalactic cloud of the Milky Way Galaxy is likely spherical?

The outer halo stars are distributed into a sphere

What causes a supernova event? Where is the energy of a supernova event from?

The outer layers of the star collapse due to a lack of pressure pushing it out. It then rebounds off of the dense core and explodes into space. The energy comes from the gravitational energy

What is the spinning Lighthouse Model for pulsars?

The particles are focused by the magnetic poles and sweep out a small area. We get a pulse twice every rotation

If you were concerned about space weather and wanted to avoid it, where would be the safest place on Earth for you to live?

The people at the equator are the safest people at the time of a solar storm as the earth's magnetic field goes from north pole to south poole, so the magnetic field around the equator is maximum. At the time of a solar storm, when the storm moves the field around, it travels through the electrical lines at the poles. That development of magnetic lines through electrical lines causes currents to be induced in them, so it would be risky at poles during a storm, but at the equator it would be less dangerous

anthropic principle

The physical laws of the universe that allow us to exists

What will happen if a planet loses angular momentum?

The planet's orbital radius decreases (gets closer to the star)

Find the reason why direct detections of molecular-cloud collapse are nearly impossible.

The process of star formation takes a long time to fully observe. Also, it is sometimes difficult to observe in the infrared spectrum as the light is blocked by larger molecules

How do stars lose mass as they age?

The proton-proton chain has a lower final mass than initial mass, so the star transforms mass into energy over the course of its lifetime

What is the Schwarzschild radius of a black hole? How can you calculate it?

The radius to which an object needs to collapse so that its escape velocity is the speed of light. R = (2GM)/(c^2)

How does the rate of hydrogen fusion change as the star ages?

The rate accelerates as it gets older

While dust clouds are too cold to radiate a measurable amount of energy in the visible part of the spectrum, they glow brightly in the infrared. Why is this?

The reason is that small dust grains absorb visible light and ultraviolet radiation very efficiently. The grains are heated by the absorbed radiation, typically to temperatures from 10 to about 500 K, and re-radiate this heat at infrared wavelengths.

Why can a red giant easily lose mass?

The red giant has a lower escape velocity because its larger, so it can eject the outer layers

What is the Local Fluff?

The region in the local bubble that has higher density and temperature (where we are).

What's the Weber-Fechner Law? What does this law mean? Find an example.

The relationship between physical intensity and perceived sensation. Perceived and actual sensation are not proportional and are dependent not the severity of stimuli one is subjected to. [the tv sounding too loud when at same value]

The Empire

The rightrul and honorable rulers and protectors of the galaxy. The rebels will be defeated. Long live the emperor

Monolithic Collapse Model

The rotating protogalactic cloud collapses due to gravity forming a galaxy. Halo stars & globular clusters were formed prior to the collapse or elsewhere

Luminosity to mass

The rotational velocity of a galaxy can be used to get intrinsic luminosity. Comparing the luminosity to the apparent brightness can be used to calculate distance

One method for indirect detection of exoplanets is Doppler, what is the other?

The second method for indirect detection of exoplanets is based not on the motion of the star but on its brightness. When the orbital plane of the planet is tilted or inclined so that it is viewed edge-on, we will see the planet cross in front of the star once per orbit, causing the star to dim slightly; this event is known as transit. Figure 21.19 shows a sketch of the transit at three time steps: (1) out of transit, (2) the start of transit, and (3) full transit, along with a sketch of the light curve, which shows the drop in the brightness of the host star. The amount of light blocked—the depth of the transit—depends on the area of the planet (its size) compared to the star. If we can determine the size of the star, the transit method tells us the size of the planet.

What is the second step in the sun's nuclear reaction process?

The second step in forming helium from hydrogen is to add another proton to the deuterium nucleus to create a helium nucleus that contains two protons and one neutron (Figure 16.7). In the process, some mass is again lost and more gamma radiation is emitted. Such a nucleus is helium because an element is defined by its number of protons; any nucleus with two protons is called helium. But this form of helium, which we call helium-3 (and write in shorthand as 3He) is not the isotope we see in the Sun's atmosphere or on Earth. That helium has two neutrons and two protons and hence is called helium-4 (4He).

What's the Surface Gravity of a star? What's the relation between the surface gravity and the stellar pressure of a star?

The surface gravity is the gravity measured at the stellar surface. To stay in equilibrium, a higher surface pressure needs a higher surface gravity

What is a geodesic curve?

The shortest distance between two points on a surface

What will happen when a small galaxy ventures too close to our Galaxy?

The smaller galaxy is torn into a stream that goes around the halo

What is the approximate spectral class of a star with: The strongest lines are those of neutral metals and bands of titanium oxide.

The spectrum contains strong lines of neutral atoms, then t can be either a K or an M star. Whereas it contains bands of titanium oxide, it must be an M star. Examples of such types of star are Betelgeuse and Antares

What will happen for a massive star after the helium in the core was used up?

The star will shed some of its mass and shrink some, but will still be hot enough to still fuse heavier elements

Find the reason why the wind particles from a protostar escape most effectively in the direction of the star's poles.

The star's magnetic field focuses the charged particles in the stellar winds. Also, older protostars may form an accretion disk that blocks the solar winds

For spiral galaxies, how do we know that the bulges of these galaxies formed earlier, and the disk formed later?

The stars in the bulge are older than the ones in the disk also

Find why galaxies collide, but stars rarely do.

The stars themselves are tiny compared to the space between them but the same ratio does not apply for galaxies

What happens to stars when Galaxies collide

The stars themselves in this pair of galaxies will not be affected much by this cataclysmic event. Since there is a lot of space between the stars, a direct collision between two stars is very unlikely. The orbits of many stars will change altering the appearance of the galaxies

Within what radius of the Sun has its original hydrogen been partially used up?

The sun's core

How does the temperature and the luminosity of a star change as the star ages?

The temperature and, therefore, luminosity increases as the star ages

What is the effective temperature of a star?

The temperature of the star is the temperature of a blackbody with the same luminosity per surface area.

What are black dwarfs?

The theoretical remains of a white dwarf star that has cooled and no longer emits light

What is spacetime?

The three dimensions of space and time are all related

Hot stars are able to heat nearby gas to temperatures close to 10,000 K. The ultraviolet radiation from the stars also ionizes what?

The ultraviolet radiation from the stars also ionizes the hydrogen (remember that during ionization, the electron is stripped completely away from the proton). Such a detached proton won't remain alone forever when attractive electrons are around; it will capture a free electron, becoming a neutral hydrogen once more. However, such a neutral atom can then absorb ultraviolet radiation again and start the cycle over. At a typical moment, most of the atoms near a hot star are in the ionized state.

What do sunspots consist of?

The umbra, an inner darker core, and a surrounding less dark region, the penumbra

Find the reason why we can't find where the big bang happened.

The universe is expanding at every point so there is no clear center of origin

What's Olbers' Paradox and what solves it?

The universe is infinite and full of stars. So the paradox is that any line of sight should end at the surface of a star, and the universe wouldn't appear as black. The solution to the paradox is that the universe is finite, nonhomogeneous, and that the universe is non static (changing).

What's the Chandrasekhar Limit? When we are talking about the Chandrasekhar limit of a star, are we talking about the star's initial mass?

The upper mass limit of a star where the electron degeneracy pressure can no longer stop it from collapsing, which is about 1.4 solar masses

What condition is necessary to view the eclipse of a binary system? Discuss the relation between the eclipsing possibility and the orbital separation of two stars.

Their orbital plane must be flat-on from our view. It's easier to see an eclipse when the orbital radius is smaller

Do cosmic rays travel in straight lines?

Their paths are affected by magnetic and gravitational fields, so they can be curved.

Find the different types of cosmic rays?

There are galactic cosmic rays and solar energetic particles. The solar energetic particles come from the sun while the others come from outside the solar system

How can you measure if space is curved?

There are many examples of General Relativity, for example, the orbit of Mercury and gravitational lensing

Describe the ISM-Star-ISM circle.

There is material in the ISM that forms into a star. The star then blows up and turns into more material and the process starts over again

There are two special types of variable stars for which—as we will see—measurements of the light curve give us accurate distances. What are they?

These are called cepheid and RR Lyrae variables, both of which are pulsating variable stars. Such a star actually changes its diameter with time—periodically expanding and contracting, as your chest does when you breathe. We now understand that these stars are going through a brief unstable stage late in their lives.

Early galaxies

These early galaxies don't have identifiable spiral arms, disks, and bulges, tend to be clumpier

Where do the heavy elements (silicon and iron) come from?

These heavier elements are formed in massive stars that are hot enough and have high enough pressure to fuse up to iron

Why can dark matter not be white or brown dwarfs, or black holes?

These objects do not contain enough mass to account for the gravitational effects of dark matter

Measurements of the widths of spectral lines show that many stars rotate faster than the Sun, some with periods of less than a day! What happens to them?

These rapid rotators spin so fast that their shapes are "flattened" into what we call oblate spheroids. An example of this is the star Vega, which rotates once every 12.5 hours. Vega's rotation flattens its shape so much that its diameter at the equator is 23% wider than its diameter at the poles (Figure 17.15). The Sun, with its rotation period of about a month, rotates rather slowly. Studies have shown that stars decrease their rotational speed as they age. Young stars rotate very quickly, with rotational periods of days or less. Very old stars can have rotation periods of several months.

What's the origin of cosmic rays?

They are emitted from solar eruptions or from highly energetic events outside our solar system, like supernovae.

What are coronal holes?

They are large dark regions of the corona that are relatively cool and quiet, and within these regions, magnetic field lines stretch far out into space instead of looping back into the surface.

What are sunspots?

They are large, dark features seen on the surface of the sun caused by increased magnetic activity, and they look darker because the spots are typically at 2000 K lower than the bright regions around them.

What can differential rotation and convection do?

They can twist and distort the magnetic fields, causing them to grow and then decay, regenerating with opposite polarity approximately every 11 years. Calculations also show that as the fields grow stronger near solar maximum, they flow from the interior of the sun toward its surface in the form of loops. When a large loop emerges from the solar surface, it creates regions of sunspot activity.

Spiral galaxies

They consist of a central bulge, a halo, a disk, and spiral arms. The luminous parts of spiral galaxies appear to range in diameter from about 20,000 to more than 100,000 light-years. Both barred and unbarred have a large range of shapes

How do organic molecules form?

They form on dust particles with the correct chemical composition, such as H2O, CH4, NH3

Describe the 1993 Nobel prize in physics.

They found radiation from a binary pulsar (two neutron stars orbiting each other). They then detected gravitational waves from this merger

What will happen when two black holes merge?

They spiral inwards and create gravitational waves until combining

Find why even very old stars in the central bulge could be metal-rich?

They were enriched by previous generations of stars

What are the properties of the first-generation stars?

They were generally hotter and larger. They didn't live very long

What will happen if interstellar grains are incorporated into newly forming stars?

They're just destroyed by the high temperature of the star.

Why is it hard to detect hydrogen lines in the cold Neutral Hydrogen Clouds?

They're weak because the transition doesn't happen too often

What does the cosmic distance ladder allow astronomers to do?

This chain of methods allows astronomers to push the limits when looking for even more distant stars. Recent work, for example, has used RR Lyrae stars to identify dim companion galaxies to our own Milky Way out at distances of 300,000 light-years. The H-R diagram method was recently used to identify the two most distant stars in the Galaxy: red giant stars way out in the halo of the Milky Way with distances of almost 1 million light-years. We can combine the distances we find for stars with measurements of their composition, luminosity, and temperature.

Plasma acts much like a hot gas, which is easier to describe mathematically than either liquids or solids. The particles that constitute a gas are in rapid motion, frequently colliding with one another. This constant bombardment is the pressure of the gas is what?

This constant bombardment is the pressure of the gas. More particles within a given volume of gas produce more pressure because the combined impact of the moving particles increases with their number. The pressure is also greater when the molecules or atoms are moving faster. Since the molecules move faster when the temperature is hotter, higher temperatures produce higher pressure.

When the spectra of different stars were first observed, astronomers found that they were not all identical. Since the dark lines are produced by the chemical elements present in the stars, astronomers first thought that the spectra differ from one another because stars are not all made of the same chemical elements. Is this true?

This hypothesis turned out to be wrong. The primary reason that stellar spectra look different is because the stars have different temperatures. Most stars have nearly the same composition as the Sun, with only a few exceptions.

What is the triple-alpha process?

Three helium atoms fuse into a single carbon atom

Why is a higher temperature required to fuse hydrogen to helium by means of the CNO cycle than is required by the process that occurs in the Sun, which involves only isotopes of hydrogen and helium?

This is because the CNO uses carbon, nitrogen and oxygen, whose atomic charges are greater than that of the elements involved in the proton-proton chain, so it is more difficult to fuse these atoms of stronger charge, as they then need greater temperature and pressure to achieve the necessary speed for fusion

Why can a flare be observable in visible light despite being so bright in x-ray and UV light?

This is because the radiations are emitted along the entire EM spectrum, which includes the visible light as well

Why is it that flares, sunspots, and bright regions in the chromosphere and corona tend to occur together on the sun in time and space, but are located at different heights of the atmosphere?

This is because they all occur together, and they vary with the sunspot cycle

What is interstellar reddening?

This occurs because interstellar dust absorbs blue light more than red light, so the absorption and scattering effects blue light and leaves red light.

Mass-to-Light Ratio

This ratio can tell us what kind of stars or making up the luminous population of the galaxy and if lots of dark matter is present. More dark matter the higher the mass is to light. Galaxies with younger stars have ratios of 1 to 10. Older stellar populations that have stopped shining have ratios of 10 to 20. With dark matter present ratio can be up to 100

Now, think back to our discussion of star surveys. It is difficult to plot an H-R diagram that is truly representative of all stars because most stars are so faint that we cannot see those outside our immediate neighborhood. The stars plotted in Figure 18.14 were selected because their distances are known. What was omitted then and why?

This sample omits many intrinsically faint stars that are nearby but have not had their distances measured, so it shows fewer faint main-sequence stars than a "fair" diagram would. To be truly representative of the stellar population, an H-R diagram should be plotted for all stars within a certain distance. Unfortunately, our knowledge is reasonably complete only for stars within 10 to 20 light-years of the Sun, among which there are no giants or supergiants. Still, from many surveys (and more can now be done with new, more powerful telescopes), we estimate that about 90% of the true stars overall (excluding brown dwarfs) in our part of space are main-sequence stars, about 10% are white dwarfs, and fewer than 1% are giants or supergiants.

Dust does not interact with all the colors of light the same way. Much of the violet, blue, and green light from these stars has been scattered or absorbed by dust, so it does not reach Earth. Some of their orange and red light, with longer wavelengths, on the other hand, more easily penetrates the intervening dust and completes its long journey through space to enter Earth-based telescopes (Figure 20.15). How does a star look as a result?

Thus, the star looks redder from Earth than it would if you could see it from nearby. (Strictly speaking, reddening is not the most accurate term for this process, since no red color is added; instead, blues and related colors are subtracted, so it should more properly be called "deblueing.") In the most extreme cases, stars can be so reddened that they are entirely undetectable at visible wavelengths and can be seen only at infrared or longer wavelengths

What are globular Clusters?

Tightly bound spherical group of stars that are bound together by gravity

How do we know the age of the sun?

To determine the age of the sun, scientists have measured the age of other elements that were present at the time of the formation fo the sun. We think that the sun and the planets formed together in a nebula while some of the bodies began orbiting the planets and became satellites. Hence, in order to determine the age of the sun, scientists estimated the age of the sun to be about the age of the earth and moon by studying moon rocks which hold primitive material.

What is the third step of the sun's nuclear reaction process?

To get to helium-4 in the Sun, helium-3 must combine with another helium-3 in the third step of fusion (illustrated in Figure 16.8). Note that two energetic protons are left over from this step; each of them comes out of the reaction ready to collide with other protons and to start step 1 in the chain of reactions all over again.

How do we know the age of our Galaxy?

Took the ages of the oldest globular clusters and halo stars

What is the difference between transit and eclipse?

Transit is when the intermediary body covers the edge body partially, an eclipse is almost entirely or entirely

How can you detect exoplanets?

Transit, doppler effect, and gravitational lensing.

Find the typical luminosity of a Quasar

Trillions of suns

Find the reason why the triple-alpha process involves three helium nuclei and not just two.

Two helium nuclei is not a stable nuclear structure

Compare the typical speed of ejected material from a supernova and the Sun.

Typical speed is 10000 km/s with a max of 20000 km/s. CME's are typically no more than 1000 km/s

Find the relationships between stellar mass, stellar temperature, and stellar luminosity. Explain the relations.

Typically higher temperature = higher luminosity. Higher mass typically would have higher luminosity. All three are directly proportional

What is a fluorescence process?

Ultraviolet waves emitted from excited state

What is escape velocity? How can you calculate the escape velocity of an object?

Velocity needed to escape a gravitational pull. Vesc = (2GM/r)½

The very hot stars required to produce H II regions are rare, and only a small fraction of interstellar matter is close enough to such hot stars to be ionized by them. Most of the volume of the interstellar medium is filled with neutral (nonionized) hydrogen. How do we go about looking for it?

Unfortunately, neutral hydrogen atoms at temperatures typical of the gas in interstellar space neither emit nor absorb light in the visible part of the spectrum. Nor, for the most part, do the other trace elements that are mixed with the interstellar hydrogen. However, some of these other elements can absorb visible light even at typical interstellar temperatures. This means that when we observe a bright source such as a hot star or a galaxy, we can sometimes see additional lines in its spectrum produced when interstellar gas absorbs light at particular frequencies (see Figure 20.4). Some of the strongest interstellar absorption lines are produced by calcium and sodium, but many other elements can be detected as well in sufficiently sensitive observations

Find the solutions for Olber's paradox?

Universe is not constant and homegeneous

Dark Matter

Unknown composition and undetectable by telescope. Detected by gravitational effects on the motions of luminous matter

What causes the expansion of the Universe?

Unknown forces theorized to be dark energy but no one knows what that is either

Find the number of galaxies in the Universe.

Up to 2 trillion

How can we deal with false positives in a transit survey?

Use other tests that are usually used to determine if it's a star or planet.

Compare the luminosity of RR Lyrae and Cepheid variables, and discuss which type of variables can be used to measure a greater distance.

Using Cepheids we can measure much farther distances because of its luminosity and duration.

How can you calculate the binary mass?

Using Kepler's third law with the orbits of the stars

How do we estimate the mass of our milky way galaxy or a spiral galaxy?

Using keplers law but on the suns orbit around the galaxy

How do we estimate the mass of the Sun?

Using keplers third law using earths orbit around the sun

How can you measure the size of an eclipsing binary?

Using the light curve; changes in luminosity resulting from an eclipse allow you to calculate diameter of the stars involved

Expansion of universe accelerating

Using type 1 supernova standard bulbs astronomers measured the rate of expansion of galaxies billions of years ago. Found that expansion was accelerating not decelerating as was expected. So hubble constant is not applicable over large spans of space and time

How much mass would a star lose because of a supernova event?

Usually close to 5 solar masses (⅝ of its mass)

Why is it hard to find dwarf galaxies?

Very faint and not very big. Luminosity similar to just a globular cluster

What are stellar associations?

Very loosely bound cluster of stars that are no longer gravitationally bound and are travelling through space together. Looser than even an open cluster.

In the early universe, what mechanism concentrated nearly smooth matter into lumps.

Vribating hot matter being condensed by gravity

How can you find a black hole?

We can find it gravitationally, and also emissions from the material falling into it. Also possibly quasars

What stellar properties can we get from the stellar spectrum?

We can get composition, temperature, pressure, rotational velocity, radial velocity, magnetic field strength, and density.

We can measure the distance of Cepheid and RR Lyrae variables, but How can we measure the distance of a star that is not variable?

We can use parallax (4→ 30,000 light-years), we can use RR Lyrae for mid distances, and Cepheids for longer distances; estimates based on the HR diagram for distances out to a million light-years or greater.

How can we measure the size of the Sun?

We measure its angular diameter and then multiply it by its distance to the earth.

How do we measure proper motion?

We measure the proper motion of a star in arcseconds (1/3600 of a degree) per year. That is, the measurement of proper motion tells us only by how much of an angle a star has changed its position on the celestial sphere. If two stars at different distances are moving at the same velocity perpendicular to our line of sight, the closer one will show a larger shift in its position on the celestial sphere in a year's time.

What is the origin of elements that are heavier than iron?

We originally thought only supernovae, but have also discovered that neutron star mergers can also produce these high mass elements

What would we observe if an extended object suddenly flares up?

We would observe it depending on how far away it was if the object was 10 ly away then we would see it after 10 years

Discuss the selection effect of the transit method.

We'd only see larger exoplanets because they'd create the most noticeable dips in light curves, so smaller planets may go undetected

How can CMEs effect normal people?

When a CME reaches Earth, it distorts Earth's magnetic field. Since a changing magnetic field induces electrical current, the CME accelerates electrons, sometimes to very high speeds. These "killer electrons" can penetrate deep into satellites, sometimes destroying their electronics and permanently disabling operation. This has happened with some communications satellites, messing up stuff like wifi and cable too, especially during a solar maximum

Galactic Mergers and Collisions

When a larger galaxy exerts its gravity on a smaller galaxy the smaller galaxies stars are spread into a stream that orbits the halo of the larger galaxy

What is the spin-orbit misalignment of a planetary system? How can we measure it? Why does it challenge the conventional planetary formation model?

When a planet orbits around a different axis than its star rotates. We can measure it by combining the transit and radial method. It's unexpected because we assumed planets and stars formed in the same spinning ball of gas, therefore spinning in the same direction.

What is starburst?

When galaxies collide their interstellar matter condenses and forms many new stars

Line Broadening

When some stars provide blueshifts and others provide redshifts, they create a wider or broader absorption or emission feature than would the same lines in a hypothetical galaxy in which the stars had no orbital motion. The amount by which each line broadens indicates the range of speeds at which the stars are moving with respect to the center of the galaxy.

Universe Becomes Transparent

When temperature dropped to 3000K the electrons and nuclei made stable atoms. Without the free electrons to scatter photons the universe became transparent allowing electromagnetic radiation to travel

What is spaghettification?

When the part closer to a black hole gets pulled much faster than the part further away

What is tidal force?

When there are different forces at different points on an object because there are different magnitudes of force acting on different parts of an object

merger

When two galaxies of equal size are involved in a collision

Explain the type Ia supernova in the stellar evolution process.

White dwarf with a companion star. When the companion star gives material too fast to the white dwarf and it excedes 1.4 solar masses it goes supernova

A fluorescent light on Earth works using the same principles as a fluorescent H II region. When you turn on the current, what happens?

When you turn on the current, electrons collide with atoms of mercury vapor in the tube. The mercury is excited to a high-energy state because of these collisions. When the electrons in the mercury atoms return to lower-energy levels, some of the energy they emit is in the form of ultraviolet photons. These, in turn, strike a phosphor-coated screen on the inner wall of the light tube. The atoms in the screen absorb the ultraviolet photons and emit visible light as they cascade downward among the energy levels. (The difference is that these atoms give off a wider range of light colors, which mix to give the characteristic white glow of fluorescent lights, whereas the hydrogen atoms in an H II region give off a more limited set of colors.)

Gas and dust are generally intermixed in space, although the proportions are not exactly the same everywhere. The presence of dust is apparent in many photographs of emission nebulae in the constellation of Sagittarius, where we see an H II region surrounded by a blue reflection nebula. Which type of nebula appears brighter depends on what?

Which type of nebula appears brighter depends on the kinds of stars that cause the gas and dust to glow. Stars cooler than about 25,000 K have so little ultraviolet radiation of wavelengths shorter than 91.2 nanometers—which is the wavelength required to ionize hydrogen—that the reflection nebulae around such stars outshine the emission nebulae. Stars hotter than 25,000 K emit enough ultraviolet energy that the emission nebulae produced around them generally outshine the reflection nebulae.

What's type I of supernovae? Why can it be used as standard bulbs?

White dwarf supernovas that all have about the same constant luminosity

What might the Universe be like in the distant future?

Will continue to cool and get darker as the universe expands

What heated the local Bubble?

Winds from stars and supernovae explosions

Is the Milky Way Galaxy purely formed from a single rotating cloud?

Yes

Dark matter is distributed in galaxies. Is there dark matter distributed among galaxies?

Yes it's the dominant mass

Is our Sun a variable star?

Yes our sun is a variable star because the apparent brightness changes over the 11-year sunspot cycle

Find the relation between the stellar lifetime and stellar mass.

Younger stars would have more mass than later as they burn off a lot of mass. If they have a higher initial mass, they'd have a longer lifetime

Rank three different types of stellar clusters by age.

Youngest to oldest: Stellar Associations, Open Clusters, and then Globular Clusters

luminosity class

a classification of a star according to its luminosity within a given spectral class; our Sun, a G2V star, has luminosity class V, for example

Superclusters

a group of galaxy clusters found in huge filamentary structures

energy is emitted when the electron does a flip, something like an acrobat in a circus flipping upright after standing on his head. The flip works like this:

a hydrogen atom consists of a proton and an electron bound together. Both the proton and the electron act is if they were spinning like tops, and spin axes of the two tops can either be pointed in the same direction (aligned) or in opposite directions (anti-aligned). If the proton and electron were spinning in opposite directions, the atom as a whole would have a very slightly lower energy than if the two spins were aligned (Figure 20.5). If an atom in the lower-energy state (spins opposed) acquired a small amount of energy, then the spins of the proton and electron could be aligned, leaving the atom in a slightly excited state. If the atom then lost that same amount of energy again, it would return to its ground state. The amount of energy involved corresponds to a wave with a wavelength of 21 centimeters; hence, it is known as the 21-centimeter line.

A graph that shows how the brightness of a variable star changes with time is called what?

a light curve. The maximum is the point of the light curve where the star has its greatest brightness; the minimum is the point where it is faintest. If the light variations repeat themselves periodically, the interval between the two maxima is called the period of the star.

white dwarf

a low-mass star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size; such a star is near its final state of life

WIMPs, weakly interacting massive particles.

a possible elementary particle that could make up dark matter that is yet to be discovered. Do not participate in nuclear reactions

What is the Maunder Minimum?

a prolonged solar minimum from about 1645-1715, during one of the coldest periods of the little ice age. This 70 year period would suggest a causal effect between decreased sunspot abundance and cooling in the north Atlantic region

deuterium

a proton and a neutron together or a hydrogen nucleus with a neutron in it formed in the first 4 minutes

The contrast between these two samples of stars, those that are close to us and those that can be seen with the unaided eye, is an example of what?

a selection effect. When a population of objects (stars in this example) includes a great variety of different types, we must be careful what conclusions we draw from an examination of any particular subgroup. Certainly we would be fooling ourselves if we assumed that the stars visible to the unaided eye are characteristic of the general stellar population; this subgroup is heavily weighted to the most luminous stars. It requires much more effort to assemble a complete data set for the nearest stars, since most are so faint that they can be observed only with a telescope. However, it is only by doing so that astronomers are able to know about the properties of the vast majority of the stars, which are actually much smaller and fainter than our own Sun. In the next section, we will look at how we measure some of these properties.

quiescent supermassive black hole reactivates

a star in the area could occasionally get close to it. Then the powerful tidal forces of the black hole can pull the whole star apart into a stream of gas. This stream quickly forms an accretion disk that gives off energy in the normal way and makes the black hole region into a temporary quasar. Will be gone in a few weeks to months

In order to specify the exact color of a star, astronomers normally measure what?

a star's apparent brightness through filters, each of which transmits only the light from a particular narrow band of wavelengths (colors). One commonly used set of filters in astronomy measures stellar brightness at three wavelengths corresponding to ultraviolet, blue, and yellow light. The filters are named: U (ultraviolet), B (blue), and V (visual, for yellow). These filters transmit light near the wavelengths of 360 nanometers (nm), 420 nm, and 540 nm, respectively. The brightness measured through each filter is usually expressed in magnitudes. The difference between any two of these magnitudes—say, between the blue and the visual magnitudes (B-V)—is called a color index.

What's the Magellanic Stream?

a stream of high-velocity clouds of gas extending from the Large and Small Magellanic Clouds

pulsating variable star

a variable star that pulsates in size and luminosity

brown dwarf

an object intermediate in size between a planet and a star; the approximate mass range is from about 1/100 of the mass of the Sun up to the lower mass limit for self-sustaining nuclear reactions, which is about 0.075 the mass of the Sun; brown dwarfs are capable of deuterium fusion, but not hydrogen fusion

What do CMEs do to space weather?

as an erupting bubble of tens of millions of tons of gas blown away from the sun into space, when it reaches earth a few days after leaving the sun, it heats the ionosphere, making it expand and reach farther into space, resulting in friction between the atmosphere and spacecraft increase, dragging satellites to lower altitudes.

What do astronomers define a metal as?

astronomers use the term "metals" to refer to all elements heavier than hydrogen and helium. The fraction of a star's mass that is composed of these elements is referred to as the star's metallicity. The metallicity of the Sun, for example, is 0.02, since 2% of the Sun's mass is made of elements heavier than helium.

"Quiescent."

black holes don't show any signs of quasar emission. But with more gas can be reactivated

The Doppler method allows us to estimate the mass of a planet. If the same object can be studied by both the Doppler and transit techniques, we can measure...what?

both the mass and the size of the exoplanet. This is a powerful combination that can be used to derive the average density (mass/volume) of the planet. In 1999, using measurements from ground-based telescopes, the first transiting planet was detected orbiting the star HD 209458. The planet transits its parent star for about 3 hours every 3.5 days as we view it from Earth. Doppler measurements showed that the planet around HD 209458 has about 70% the mass of Jupiter, but its radius is about 35% larger than Jupiter's. This was the first case where we could determine what an exoplanet was made of—with that mass and radius, HD 209458 must be a gas and liquid world like Jupiter or Saturn.

What are the Fermi Bubbles?

bubbles around the center of the galaxy created by jets from the quasar

Dusty clouds in space betray their presence in several ways:

by blocking the light from distant stars, by emitting energy in the infrared part of the spectrum, by reflecting the light from nearby stars, and by making distant stars look redder than they really are.

The H-R diagram method allows astronomers to estimate distances to nearby stars, as well as some of the most distant stars in our Galaxy, but it is anchored by what?

by measurements of parallax. The distances measured using parallax are the gold standard for distances: they rely on no assumptions, only geometry. Once astronomers take a spectrum of a nearby star for which we also know the parallax, we know the luminosity that corresponds to that spectral type. Nearby stars thus serve as benchmarks for more distant stars because we can assume that two stars with identical spectra have the same intrinsic luminosity.

How can the solar magnetic field be measured?

by using the Zeeman effect, as an atom has many energy levels and spectral lines that are formed when electrons shift from one level to another, and if each energy level is precisely defined, then the difference between them is also quite precise, so as an electron changes levels, the result is a sharp, narrow spectral line. In the presence of a strong magnetic field, however, each energy level is separated into several levels very close to one another and the separation of these levels is proportional to the strength of the field. As a result, spectral lines formed in the presence of a magnetic field are not single lines, but a series of very closely spaced lines corresponding to the subdivisions of the energy levels.

Each of these spectral classes, except possibly for the Y class which is still being defined, is further subdivided into 10 subclasses. How are they organized?

designated by the numbers 0 through 9. A B0 star is the hottest type of B star; a B9 star is the coolest type of B star and is only slightly hotter than an A0 star.

When can you see the corona and chromosphere?

during a total solar eclipse, in fact, the corona emits half as much light as the full moon, so its light is usually overpowered by the photosphere

Unless convection occurs, the only significant mode of energy transport through a star is by what?

electromagnetic radiation. Radiation is not an efficient means of energy transport in stars because gases in stellar interiors are very opaque, that is, a photon does not go far (in the Sun, typically about 0.01 meter) before it is absorbed. (The processes by which atoms and ions can interrupt the outward flow of photons—such as becoming ionized—were discussed in the section on the Formation of Spectral Lines.) The absorbed energy is always reemitted, but it can be reemitted in any direction. A photon absorbed when traveling outward in a star has almost as good a chance of being radiated back toward the center of the star as toward its surface.

The Sun, like the majority of other stars, is stable; it is neither expanding nor contracting. Such a star is said to be in a condition of what?

equilibrium. All the forces within it are balanced, so that at each point within the star, the temperature, pressure, density, and so on are maintained at constant values while only changing quasi-statically

The traditional model for the formation of planets works only if the giant planets are formed where?

far from the central star (about 5-10 AU), where the disk is cold enough to have a fairly high density of solid matter. It cannot explain the hot Jupiters, which are located very close to their stars where any rocky raw material would be completely vaporized. It also cannot explain the elliptical orbits we observe for some exoplanets because the orbit of a protoplanet, whatever its initial shape, will quickly become circular through interactions with the surrounding disk of material and will remain that way as the planet grows by sweeping up additional matter.

What happens near sunspot maximum?

flares are more likely to occur and the corona is much more conspicuous at that time

Our computer models of how stars evolve over time show us that a typical star will spend about 90% of its life doing what?

fusing the abundant hydrogen in its core into helium. This then is a good explanation of why 90% of all stars are found on the main sequence in the H-R diagram. But if all the stars on the main sequence are doing the same thing (fusing hydrogen), why are they distributed along a sequence of points? That is, why do they differ in luminosity and surface temperature (which is what we are plotting on the H-R diagram)?

active galactic nuclei (AGN)

galaxies that are almost as luminous as quasars and share many of their properties, although to a less spectacular degree; abnormal amounts of energy are produced in their centers

active galaxies

galaxies that house active galactic nuclei

If the growing planets reach a mass bigger than about 10 times the mass of Earth, their gravity is strong enough to capture and hold on to what?

hydrogen gas that remains in the disk. At that point, they will grow in mass and radius rapidly, reaching giant planet dimensions. However, to do so requires that the rapidly evolving central star hasn't yet driven away the gas in the disk with its increasingly vigorous wind (see the earlier section on Star Formation). From observations, we see that the disk can be blown away within 10 million years, so growth of a giant planet must also be a very fast process, astronomically speaking.

cold dark matter

if the dark matter particles moved slowly and covered only small distances compared to the sizes of the lumps in the early universe. Their slow speeds and energy would mean that even the smaller lumps of ordinary matter would survive to grow into small galaxies.

What are some ways that the spectra of stars change with temperature?

in the hottest O stars (those with temperatures over 28,000 K), only lines of ionized helium and highly ionized atoms of other elements are conspicuous. Hydrogen lines are strongest in A stars with atmospheric temperatures of about 10,000 K. Ionized metals provide the most conspicuous lines in stars with temperatures from 6000 to 7500 K (spectral type F). In the coolest M stars (below 3500 K), absorption bands of titanium oxide and other molecules are very strong. By the way, the spectral class assigned to the Sun is G2.

List ways that determine the age of the universe.

inverse of hubble constant, looking at how old distant galaxies are

The second technique for obtaining information about the Sun's interior involves what?

involves the detection of a few of those elusive neutrinos created during nuclear fusion. Recall from our earlier discussion that neutrinos created in the center of the Sun make their way directly out of the Sun and travel to Earth at nearly the speed of light. As far as neutrinos are concerned, the Sun is transparent.

Problems with the Standard Big Bang Model

it does not explain why the density of the universe is equal to the critical density. And the uniformity of the universe because accepting the Standard Big Bang Model means that not all parts of the visible universe were not in contact at any time so measuring in two opposite directions that could not have made contact with each other yet due to their horizon distances why are their temperatures the same unless the universe started out being uniform

What does the strong nuclear force do?

it holds the particles inside the nucleus together, and nuclear energy is released when particles come together under this force and form a nucleus. AKA the binding energy. This is similar to when a star shrinks under the force of gravity, it brings its atoms closer together and gravitational energy is released

What is an active region?

it is a place on the sun where a number of phenomena such as flares and sunspots are seen. These regions are always associated with strong magnetic fields

What is the most violent event on the surface of the sun?

it is a rapid eruption with energy equating to a million hydrogen bombs, a solar flare.

What is the solar wind?

it is the stream of charged particles that are produced in the sun's atmosphere, and they exist because the gases in the corona are so hot and moving so rapidly that they cannot be held back by solar gravity

very large elliptical galaxies

likely form by cannibalizing a variety of smaller galaxies in their clusters. Frequently possess more than one nucleus and have probably acquired their unusually high luminosities by swallowing nearby galaxies. The multiple nuclei are the remnants of their victims.

How massive are most stars in comparison to the sun?

most stars are not as massive as the sun. In fact, stars more massive than the sun are rare

One technique, which gives very precise diameters but can be used for only a few stars, is to do what?

observe the dimming of light that occurs when the Moon passes in front of a star. What astronomers measure (with great precision) is the time required for the star's brightness to drop to zero as the edge of the Moon moves across the star's disk. Since we know how rapidly the Moon moves in its orbit around Earth, it is possible to calculate the angular diameter of the star. If the distance to the star is also known, we can calculate its diameter in kilometers. This method works only for fairly bright stars that happen to lie along the zodiac, where the Moon (or, much more rarely, a planet) can pass in front of them as seen from Earth.

RR Lyrae

one of a class of giant pulsating stars with periods shorter than 1 day, useful for finding distances

Astronomers actually define parallax to be what?

one-half the angle that a star shifts when seen from opposite sides of Earth's orbit. The reason for this definition is just that they prefer to deal with a baseline of 1 AU instead of 2 AU.

What is the origin of GRBs?

originate from outside the galaxy

An apparent change in direction of the remote object due to a change in vantage point of the observer is called what? (close one eye and look at thumb with each eye separately)

parallax

Radiative zone

photons bounce off of one another as they lose energy and try to reach the convection zone

The Sun is so hot that all of the material in it is in the form of an ionized gas, called what?

plasma

Convection zone

plasma at the bottom of the zone is extremely hot, and it bubbles to the surface where it loses its heat to space. Once the plasma cools, it sinks back to the bottom of the convection zone

There is another type of motion stars can have that cannot be detected with stellar spectra. Unlike radial motion, which is along our line of sight (i.e., toward or away from Earth), this motion, called what?

proper motion, is transverse: that is, across our line of sight. We see it as a change in the relative positions of the stars on the celestial sphere. These changes are very slow. Even the star with the largest proper motion takes 200 years to change its position in the sky by an amount equal to the width of the full Moon, and the motions of other stars are smaller yet.

Georges Lemaître

proposed model for the big bang. Call the center point the primeval atom

if stars are moving toward or away from us, we must consider the Doppler effect. We should see all the spectral lines of moving stars shifted toward the red end of the spectrum if the star is moving away from us, or toward the blue (violet) end if it is moving toward us. The greater the shift, the faster the star is moving. Such motion, along the line of sight between the star and the observer, is called what?

radial velocity

what happens to energy when breaking apart a nuclei?

since you get binding energy when forming the nuclei, the particles take in energy and gains mass when breaking apart, so delta E is positive for the nuclei for fission, and for fusion delta E is negative since it is being released

Local Group

small group of galaxies close together that also contains the Milky Way

What is the true velocity of a star

space velocity, which requires knowledge of radial velocity, proper motion, and distance

List methods that determine the age of stars.

spectrum, age of nearby stars, HR diagram

Typical individual grains must be just slightly smaller than the wavelength of visible light. If the grains were a lot smaller, they would not block the light efficiently, however, if the dust grains were much larger than the wavelength of light, then starlight would do what?

starlight would not be reddened. Things that are much larger than the wavelength of light would block both blue and red light with equal efficiency. In this way we can deduce that a characteristic interstellar dust grain contains 106 to 109 atoms and has a diameter of 10-8 to 10-7 meters (10 to 100 nanometers). This is actually more like the specks of solid matter in cigarette smoke than the larger grains of dust you might find under your desk when you are too busy studying astronomy to clean properly.

As the star and planet orbit each other, part of their motion will be in our line of sight (toward us or away from us). Such motion can be measured using

the Doppler effect and the star's spectrum. As the star moves back and forth in orbit around the system's center of mass in response to the gravitational tug of an orbiting planet, the lines in its spectrum will shift back and forth.

The expansion and contraction of pulsating variables of a star can be measured by using

the Doppler effect. The lines in the spectrum shift toward the blue as the surface of the star moves toward us and then shift to the red as the surface shrinks back. As the star pulsates, it also changes its overall color, indicating that its temperature is also varying. And, most important for our purposes, the luminosity of the pulsating variable also changes in a regular way as it expands and contracts.

Absorption lines of a majority of the known chemical elements have now been identified in the spectra of the Sun and stars. If we see lines of iron in a star's spectrum, for example, then we know immediately that the star must contain iron. So, then, what does the absence of an element's spectral lines mean?

the absence of an element's spectral lines does not necessarily mean that the element itself is absent. As we saw, the temperature and pressure in a star's atmosphere will determine what types of atoms are able to produce absorption lines. Only if the physical conditions in a star's photosphere are such that lines of an element should (according to calculations) be there can we conclude that the absence of observable spectral lines implies low abundance of the element. Suppose two stars have identical temperatures and pressures, but the lines of, say, sodium are stronger in one than in the other. Stronger lines mean that there are more atoms in the stellar photosphere absorbing light. Therefore, we know immediately that the star with stronger sodium lines contains more sodium. Complex calculations are required to determine exactly how much more, but those calculations can be done for any element observed in any star with any temperature and pressure.

critical density

the mass per unit volume that will be just enough to slow the expansion to zero at some time infinitely far in the future. If the actual density is higher than this critical density, then the expansion will ultimately reverse and the universe will begin to contract. If the actual density is lower, then the universe will expand forever.

To summarize, a good measurement of the motion of two stars around a common center of mass, combined with the laws of gravity, allows us to determine what?

the masses of stars in such systems. These mass measurements are absolutely crucial to developing a theory of how stars evolve. One of the best things about this method is that it is independent of the location of the binary system. It works as well for stars 100 light-years away from us as for those in our immediate neighborhood.

Proxima Centauri is an example of what?

the most common type of star, and our most common type of stellar neighbor (as

What and where are prominances?

they usually originate near sunspots, and they are higher in the sun's atmosphere than plages. during an eclipse, plages can be seen as red features rising above the eclipsed sun, reaching high into the corona. In fact, the quiescent prominences (different type) are graceful loops of plasma that can remain nearly stable for hours, or even days.

Calculations show that if a planet forms while a substantial amount of gas remains in the disk, then some of the planet's orbital angular momentum can be transferred to the disk. As it loses momentum, what happens?

the planet will spiral inward. This process can transport giant planets, initially formed in cold regions of the disk, closer to the central star—thereby producing hot Jupiters. Gravitational interactions between planets in the chaotic early solar system can also cause planets to slingshot inward from large distances. But for this to work, the other planet has to carry away the angular momentum and move to a more distant orbit. In some cases, we can use the combination of transit plus Doppler measurements to determine whether the planets orbit in the same plane and in the same direction as the star. For the first few cases, things seemed to work just as we anticipated: like the solar system, the gas giant planets orbited in their star's equatorial plane and in the same direction as the spinning star.

What are rotation curves?

the plot of rotation velocity vs distance from center of galaxy

Astronomers discovered that the Sun pulsates—that is, it alternately expands and contracts—just as your chest expands and contracts as you breathe. This pulsation is very slight, but it can be detected by measuring what?

the radial velocity of the solar surface—the speed with which it moves toward or away from us. The velocities of small regions on the Sun are observed to change in a regular way, first toward Earth, then away, then toward, and so on. It is as if the Sun were "breathing" through thousands of individual lungs, each having a size in the range of 4000 to 15,000 kilometers, each fluctuating back and forth

Of course, knowing the sum of the masses is not as useful as knowing the mass of each star separately. But the relative orbital speeds of the two stars can tell us what?

the relative orbital speeds of the two stars can tell us how much of the total mass each star has. As we saw in our seesaw analogy, the more massive star is closer to the center of mass and therefore has a smaller orbit. Therefore, it moves more slowly to get around in the same time compared to the more distant, lower-mass star. If we sort out the speeds relative to each other, we can sort out the masses relative to each other. In practice, we also need to know how the binary system is oriented in the sky to our line of sight, but if we do, and the just-described steps are carried out carefully, the result is a calculation of the masses of each of the two stars in the system.

What happens when binding energy is released?

the resulting nucleus has slightly less mass than the sum of the masses of the particles that came together to form it, as the energy comes from the loss of mass. (E=mc^2)

What is granulation?

the rice-grain-like structure of the solar photosphere; granulation is produced by upwelling currents of gas that are slightly hotter, and therefore brighter, than the surrounding regions, which are flowing downward into the Sun

What produces the energy of ultra-hot interstellar gas

the source of energy producing these remarkable temperatures is the explosion of massive stars at the ends of their lives (Figure 20.7). Such explosions, called supernovae, occur when some stars, nearing the ends of their lives, become unstable and literally explode. These explosions launch gas into interstellar space at velocities of tens of thousands of kilometers per second (up to about 30% the speed of light). When this ejected gas collides with interstellar gas, it produces shocks that heat the gas to millions or tens of millions of degrees.

Astrophysicists have been able to show that the structure of stars that are in equilibrium and derive all their energy from nuclear fusion is completely and uniquely determined by just two quantities:

the total mass and the composition of the star

What does "the average density of the Universe" mean?

the total mass of the universe divided by its volume

expansion of the universe

the universe is the stretching of all spacetime, all points in the universe are stretching together. Thus, the expansion began everywhere at once. Therefore we don't know where the big bang happened

The Inflationary Hypothesis

the universes flatness and uniformity can be explained if shortly after the Big Bang but before the emission of CMB the universe experienced a sudden increase in size. A model universe in which this rapid, early expansion occurs is called an inflationary universe.

What is the "big crunch"?

theory that gravity will eventually stop expansion of universe and cause universe to begin to shrink

What can the sun's pulsations help us determine?

these small velocity variations can be used to determine what the interior of the Sun is like. The motion of the Sun's surface is caused by waves that reach it from deep in the interior. Study of the amplitude and cycle length of velocity changes provides information about the temperature, density, and composition of the layers through which the waves passed before they reached the surface. The situation is somewhat analogous to the use of seismic waves generated by earthquakes to infer the properties of Earth's interior. For this reason, studies of solar oscillations (back-and-forth motions) are referred to as helio-seismology.

Interstellar clouds do not last for the lifetime of the universe. Instead, what do they do?

they are like clouds on Earth, constantly shifting, merging with each other, growing, or dispersing. Some become dense and massive enough to collapse under their own gravity, forming new stars. When stars die, they, in turn, eject some of their material into interstellar space. This material can then form new clouds and begin the cycle over again.

how are flares observed?

they are often observed in the red light of hydrogen, but the visible emission is only a tiny fraction of the energy released wen a solar flare explodes. Flares seem to occur when magnetic fields pointing opposite directions release energy by interacting with and destroying each other

What are eruptive prominences?

they are prominences that send matter upward into the corona at high speeds

What do solar flares do to the space weather?

they shower the upper atmosphere of earth with x-rays, energetic particles, and intense UV radiation. These ionize atoms in earth's upper atmosphere and the freed electrons can build p a charge on the surface of a space craft and damage electronics when this static charge discharges

How can you measure the size of a hot accretion disk which emits energy?

time is takes for luminosity to vary

We can analyze a radial velocity curve to determine what?

to determine the masses of the stars in a spectroscopic binary. This is complex in practice but not hard in principle. We measure the speeds of the stars from the Doppler effect. We then determine the period—how long the stars take to go through an orbital cycle—from the velocity curve. Knowing how fast the stars are moving and how long they take to go around tells us the circumference of the orbit and, hence, the separation of the stars in kilometers or astronomical units. From Kepler's law, the period and the separation allow us to calculate the sum of the stars' masses.

binary stars

two stars that revolve about each other

What are the best standard bulbs we found and why?

type Ia supernovae astronomers have found that they all have about the same constant luminosity

Black hole influence on star formation

ways: through its jets, through winds of particles that manage to stream away from the accretion disk, and through radiation from the accretion disk. As they stream away from the black hole, all three can either promote star formation by compressing the surrounding gas and dust—or instead suppress star formation by heating the surrounding gas and shredding molecular clouds, thereby inhibiting or preventing star formation.

The fact that starlight is reddened by interstellar dust means that long-wavelength radiation is transmitted through the Galaxy more efficiently than short-wavelength radiation. Consequently, if we wish to see farther in a direction with considerable interstellar material, we should look at what?

we should look at long wavelengths. This simple fact provides one of the motivations for the development of infrared astronomy. In the infrared region at 2 microns (2000 nanometers), for example, the obscuration is only one-sixth as great as in the visible region (500 nanometers), and we can therefore study stars that are more than twice as distant before their light is blocked by interstellar dust. This ability to see farther by observing in the infrared portion of the spectrum represents a major gain for astronomers trying to understand the structure of our Galaxy or probing its puzzling, but distant, center

It is a lot easier to detect the spread-out raw material from which planets might be assembled than to detect planets after they are fully formed. From our study of the solar system, we understand that planets form by doing what?

we understand that planets form by the gathering together of gas and dust particles in orbit around a newly created star. Each dust particle is heated by the young protostar and radiates in the infrared region of the spectrum. Before any planets form, we can detect such radiation from all of the spread-out individual dust particles that are destined to become parts of planets. We can also detect the silhouette of the disk if it blocks bright light coming from a source behind it

photon decoupling time

when radiation began to stream freely through the universe without interacting with matter

galactic cannibalism

when small galaxies are swallowed by larger ones

Energy to Matter and Back Again

when subatomic particles of matter and antimatter collide, they turn into pure energy. But the reverse, energy turning into matter and antimatter, is equally possible.

Since hydrogen is the main constituent of interstellar gas, we often characterize a region of space according to what?

whether its hydrogen is neutral or ionized. A cloud of ionized hydrogen is called an H II region. (Scientists who work with spectra use the Roman numeral I to indicate that an atom is neutral; successively higher Roman numerals are used for each higher stage of ionization. H II thus refers to hydrogen that has lost its one electron; Fe III is iron with two electrons missing.)

Direct imaging works best for what?

young gas giant planets that emit infrared light and reside at large separations from their host stars. Young giant planets emit more infrared light because they have more internal energy, stored from the process of planet formation. Even then, clever techniques must be employed to subtract out the light from the host star. In 2008, three such young planets were discovered orbiting HR 8799, a star in the constellation of Pegasus (Figure 21.21). Two years later, a fourth planet was detected closer to the star. Additional planets may reside even closer to HR 8799, but if they exist, they are currently lost in the glare of the star.

Find the difference between a young galaxy and an old galaxy.

younger galaxies are smaller, clumpier, and bluer. Older galaxies have more structure and are redder

Formula for the Doppler shift for nearby objects

z = Δλ/λ= v/c λ = wavelength emitted by the source of radiation that is not moving Δλ = difference between that wavelength and the wavelength we measure v = velocity which the source moves away c = speed of light

Find the highest observed redshifts.

z=12