Astr Final

Kirchoff's 3 Laws of Spectrum Formation: 3 basic rules for how its formed

1. An incandescent solid or high dense gas (such as a blackbody) produces a continuous spectrum. 2. A hot low-density gas produces an emission-line spectrum. 3. A continuous spectrum source viewed through a cooler low-density gas produces an absorption-line spectrum.

What spectral line formations tell us about the astronomical source that produces those lines (chemical fingerprints)?

1. If the wavelength equal to the energy between orbitals hits the atom, the electron will absorb it and excite to that orbital. When it de-excites it will emit a photon with that energy 2. The chemical fingerprint is the unique pattern created by an element (Emission or absorption lines)

Laws of Thermal Radiation

1. Stefan-Boltzmann law 2. Wien's law 3. Doppler Effect

Kepler's 2nd Law: The Law of Areas

A line that connects a planet to the sun sweeps out equal areas in equal times.

Photons

A photon is the quantum of electromagnetic radiation. The term quantum is the smallest elemental unit of a quantity, or the smallest discrete amount of something.

Kepler's 1st Law: The Law of Orbits

All planets move in elliptical orbits, with the sun at one focus.

Doppler Effect

An apparent change in the frequency of waves, as of sound or light, occurring when the source and observer are in motion relative to each other, with the frequency increasing when the source and observer approach each other and decreasing when they move apart

Spectral Line Formation

An isolated bright or dark line in a spectrograph produced by emission or absorption of light of a single wavelength, generally corresponding to a specific shift in the energy of an electron moving from one orbital to another.

Relationship of Mass and Energy

Based on Einstein's equation E = mc^2, the amount of energy added is relative to the mass gained by the proton multiplied by the speed of light squared. In other words, a lot of energy is converted into a relatively small amount of mass.

White dwarfs have a wide range of sizes, they can be larger or smaller than Earth. A typical white dwarf has the mass of the Sun compressed into a volume the size of Earth.

Compare a white dwarf with the size of the Earth.

1. Surface Temp: hot when it forms, cools in time 2. Luminosity: dim compared to other stars 3. Radii: small

Compared to the main sequence stars, what are their typical: 1. surface temperatures 2. luminosities 3. radii

A nova can shine as bright as 100,000 Suns

Compared with the Sun, how bright does a nova become?

A _________ is the ball of neutrons created by the collapse of the iron core in a massive star supernova. ________ stars are small in size but extremely high in mass.

Describe a neutron star neutron

is a relatively young neutron star. The star is the central star in the ______ _________, a remnant of the supernova SN 1054, which was widely observed on Earth in the year 1054. Discovered in 1968, the pulsar was the first to be connected with a supernova remnant. The ______ Pulsar is one of very few pulsars to be identified optically. The optical pulsar is roughly 20 kilometres (12 mi) in diameter and the pulsar "beams" rotate once every 33 milliseconds, or 30 times each second

Describe the Crab Nebula pulsar

The Milky Way galaxy is partially flat disk of stars with spiral arms and a bright central bulge. The disk is surrounded by a round halo. The Milky Way galaxy holds more than 100 billion stars.

Describe the appearance and main components of our galaxy, the Milky Way.

X-RAY observations of the galactic center show an X-ray flare from the suspected black hole. INFARED observations of the galactic center show that there is a black hole in the center. Gas and dust prevent VISIBLE light to be been from the center of the galaxy.

Describe the galactic center as observed in X-rays, visible light, infrared light, and radio wavelength radiation

Each individual star follows its own orbital path around the center of the galaxy. The orbits of the stars are wavy because of the localized pull of gravity within the disk. If a star is too far above, the disk is pulled back. Halo stars swoop from high above and below the disk on randomly oriented orbits. The halo is more 'puffy' because halo stars rise above the disk greater than those of disk stars. The stellar orbits in our galaxy reveal that most of our galaxy's mass consists of invisible dark matter in the halo.

Describe the orbits of stars about the center of our galaxy. What causes the orbits to be wavy? Describe the orbits of the halo stars. Why is the halo more "puffy" than the disk? Why is there an elongated bulge of stars in our galaxy? The stellar orbits in our galaxy reveal that most of our galaxy's mass consists of _______________ in the ___?

An object falling into a black hole would rapidly accelerate and quickly cross the event horizon, but for an external observer the object would appear to take forever.

Detail what an external observer would see as an object (e.g. a person or an asteroid) fell into a black hole. What would the object/person experience?

Differences in galaxy ____ depend on the kinds of stars galaxies contain. Spiral and Irregular galaxies appear white because they contain stars of all ages and types. Elliptical galaxies look redder because they contain more old, reddish stars.

Do GALAXY colors differ? If yes, in which ways?

Heavy elements were produced by stars only containing hydrogen and helium. These elements mix with interstellar gas, raising the proportion heavy elements.

Explain how a galaxy gradually becomes enriched with elements heavier than hydrogen and helium as time goes on.

A white dwarf in a close binary system can be given new life by gradually gaining mass from its companion main-sequence star.

Explain how a white dwarf can be given new life if it has a close binary companion.

A white dwarf can reach the white dwarf mass limit by merging with its binary star companion. Two white dwarf orbiting close together emit gravitational waves, which carry energy and angular momentum away from the binary system. So, the two white dwarfs spiral towards each other, merging. If the total mass of the merge exceeds 1.4 times the mass of the Sun, white dwarf supernova will happen.

Explain how stellar mergers can occur and produce white dwarf supernovae.

The _____________ marks the point of no return for objects entering a black hole, where escape velocity equals the speed of light.

Explain the existence of an event horizon about a black hole?

____________ radius is a measure of the size of the event horizon of a black hole (a black hole with the mass of the sun has a Schwarzschild radius of 3 km).

Explain the existence of an event horizon about a black hole? What is the meaning of the Schwarzschild radius, and what is the simple formula that one can use to estimate this quantity?

When hydrogen is spilled onto the surface of a white dwarf, its strong gravity compresses the hydrogen gas into a thin surface layer. This rises the pressure and temperature as the layer builds up with more accreting gas. When the temperature reaches 10 million K, hydrogen fusion is initiated. The fusion causes a thermonuclear flash called a nova.

Explain the nova phenomenon. What is the process that leads to hydrogen fusion on the surface of the white dwarf?

White Dwarfs cannot have a mass greater than 1.4 times the mass of the Sun, because electron speeds would reach to the speed of light in a white dwarf with a mass 1.4 times the mass of the Sun.

Explain why there is a limit to the mass of a white dwarf.

They emit 100,000 times as much energy in X-rays as the Sun emits in all wavelengths of light.

How bright are X-ray Binary stars?

_________ lines can be used to deduce the temperature and chemical composition of the nebula because they reveal the atoms and ions that emit most of the light.

How can one use the emission lines to deduce the temperature and chemical composition of the nebula?

Origins of a supernova can be distinguished by the rate their luminosities fade. Luminosity of a white dwarf supernova fade steadily, while the brightness of a massive star supernova decline in a complicated way.

How can we tell that a supernova came from the explosion of a white dwarf instead of core- collapse in a massive star?

Neutron stars are small in size but extremely high in mass.

How does its size compare with that of a white dwarf?

______ ______ pulsar spins 30 times per second and it is gradually spinning slower. Eventually it will slow down to to point that its magnetic field becomes too weak to be detected

How fast does the Crab Nebula rotate?

The individual stars in the system have sizes that range from 15 to 19 times the mass of the Sun.

How massive are the individual stars in the constellation of Cygnus?

Conservation of Angular and Linear Momentum

In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational equivalent of linear momentum. It is an important quantity in physics because it is a conserved quantity - the total angular momentum of a system remains constant unless acted on by an external torque.

The compression of hydrogen is the greatest for massive white dwarfs, because they have stronger surface gravities.

Is the time interval between explosions shorter for the more massive, or the less massive white dwarfs?

Our galaxy might have begun as a protogalactic cloud of hydrogen and helium, or it may have begun from the merge of several smaller gas clouds, already bearing stars and clusters.

Is there a difference between the chemical compositions of the cool stars in the halo versus the disk? Why?

Kepler's Third Law

Johannes Kepler discovered a simple relationship between the average distance of a planet from the Sun (called its semi-major axis, A, measured in Astronomical Units) and the amount of time it takes a planet to orbit the Sun once (called its orbital period, P, measured in years). For objects orbiting the Sun, the semi-major axis to the third power equals the period squared: A^3 = P^2 There were two problems with this relation. First, Kepler did not know how it worked, he just knew it did. Second, the relation does not work for objects which are not orbiting the Sun. For example, the Moon orbiting the Earth. Isaac Newton solved both these problems with his Theory of Gravity, and discovered that the masses of the orbiting bodies also play a part. Newton developed a more general form of what was called Kepler's Third Law that could apply to any two objects orbiting a common center of mass. This is called Newton's Version of Kepler's Third Law.

3 Types of Spectra

Line is classified into continuous, absorption, and emission

Cygnus X-1 system in the constellation of Cygnus is the famous star system that harbors a black hole

Name the famous star system in the constellation of Cygnus that harbors a black hole?

The gravitational detectors in the US are LIGO observatories and they are located in Louisiana and Washington.

Name the state-of-the- art gravitational detectors in the USA.

1. Elliptical galaxies 2. Spiral galaxies 3. Irregular galaxies

Name the three main types of galaxies

On August 17, 2017, a ripple caused by a collision 130 million years ago reached Earth.

On August 17, 2017 a significant gravitational event was recorded by 70 ground-based and space-based observatories. Gamma rays were detected from the Fermi spacecraft. Analysis of the data suggests the even was cause from __________________?

Elliptical galaxies

Red, round and elongated, contain hot ionized gas, very little cool gas and dust,

Motion of Charged Particles in a Magnetic Field

Since the force is F = qvB in a constant magnetic field, a charged particle feels a force of constant magnitude always directed perpendicular to its motion. The result is a circular orbit. ... The radius of the orbit depends on the charge and velocity of the particle as well as the strength of the magnetic field.

Interaction Between Light and Matter

The photoelectric effect is one example. The threshold frequency is a characteristic of the metal as this relates to a specific energy level of the electrons which will depend on the identity of the metal. The interaction between light and matter can therefore be used for identification.

Kepler's 3rd Law: The Law of Periods

The square of the period of any planet is proportional to the cube of the semimajor axis of its orbit.

Tidal Force

The tidal force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force exerted by one body on another is not constant across it; the nearest side is attracted more strongly than the farthest side.

_______ galaxies are galaxies that have disks and halos, but they lack spiral arms.

What are Lenticular galaxies

________ binaries are binary star systems that emit x-rays, which are from accretion disks around neutron stars.

What are X-ray binaries?

_____ spirals are spiral galaxies that have a straight bar of stars cutting through the center, with spiral arms at the ends of the bar.

What are barred spirals?

___________ are sudden bursts of gamma rays from deep space, coming from distant galaxies.

What are gamma ray bursts?

Gravitational waves are ripples in the curvature of spacetime that are generated through certain interactions. Gravitational waves are detected through merging black holes.

What are gravitational waves, and how are they detected?

__________ of gas are expanding shells of hot, ionized gas moved by stellar winds or supernovae. They are created by the ejection of high-speed gas into space surrounding interstellar material.

What are hot bubbles of gas, and how are they formed?

________ nebulae are colorful, wispy clouds of gas that glow because the neighboring hot stars irradiate them with UV photons that can ionize hydrogen atoms.

What are ionization nebulae (also called emission nebulae or H II regions)?

Nova remnant is the accreted materials that are ejected by the heat and pressure nova creates.

What are nova remnants?

______________ are abrupt, high-gas-pressure walls that move faster than the speed at which sound waves can travel through interstellar space. When a wispy cloud (supernova remnant) is being observed, walls of gas that have been compressed, heated, and ionized by the outward-moving shock front is seen.

What are shock-fronts and how do they explain wispy clouds known as supernova remnants?

Due to ________________, neutron stars are extremely dense and massive compared to their 10km sizes.

What are some of the consequences of the extreme gravity at the surface of a neutron star?

______ density waves are gravitationally driven waves of enhanced density that move through a spiral galaxy and are responsible for maintaining spiral arms.

What are spiral density waves?

_____ and _________ __________ Clouds are small galaxies visible to the eye from the Southern Hemisphere. They orbit the Milky Way at distances of 160,000 and 200,000 light years. Sagittarius and Canis Major are galaxies closer to the Milky Way. These galaxies are in the process of colliding with the Milky Way.

What are the Large and Small Magellanic Clouds?

____1____ populations consist of stars that follow the orderly patterns of the disk, including both old and young stars. ____2____ populations consist of stars that orbit the center of the galaxy with many different inclinations, including only old, low-mass stars.

What are two models that could explain the difference between the halo and disk populations? 1. DISK 2. HALO

If spiral arms moved along with the stars, the central parts of the arms would wind around the galaxy many more times than the outer parts.

What argues against an interpretation that the spiral structure moves with the stars?

Two neutron stars orbiting close together emit gravitational waves and cause them to spiral together and merge. As the stars merge, the overwhelming mass acquired by the larger star causes it to collapse, and a black hole is born.

What causes them to move toward each other?

When __________ bubbles from multiple supernovae events and stellar winds from hot stars cool, eventually the shocked gas radiates away most of its original energy.

What eventually happens when merged bubbles from multiple supernovae events and stellar winds from hot stars cool?

Tidal forces are very strong near the event horizon of a black hole that they would cause an object to stretch so much that it breaks apart.

What force is very strong near the event horizon of a black hole that would cause an object to stretch so much that it breaks apart?

The time between nova explosions depend on the rate of hydrogen accretion and how highly compressed the hydrogen becomes.

What governs the time interval between nova explosions?

If a collapsing core of a neutron star exceeds this limit, it turns into a black hole.

What happens if the collapsing core of a massive star exceeds this limit?

When close neutron stars merge, they produce a blend of rare elements like GOLD and PLATINUM, most of the neutron star matter remains gravitationally bound to the system, but some of it is ejected into the interstellar space.

What happens when close neutron stars merge?

_________ is a source of radio emission.

What is Sgr A*?

A ___________ is a bottomless pit in spacetime, where nothing can escape from and nothing can be detected from after an object falls into.

What is a black hole?

A ________ is an event where the supernova that forms a black hole crushes more matter into a smaller radius, releasing gravitational potential energy.

What is a hypernova?

A ________ is a neutron star which we observe rapid pulses of radiation as it rotates

What is a pulsar?

White dwarfs are remaining 'dead' cores of former giants. Although they don't have nuclear fusion, they are hot because they are exposed stellar cores. They are dim because they lack an energy source.

What is a white dwarf, and where do they come from?

An X-ray burster is an object that emits a burst if X-rays every once in awhile, caused by the helium fusion on the surface if an accreting neutron star in a binary system. Hydrogen-rich material from the companion star builds up on the surface of the neutron star. Forming a layer. Pressures at the bottom of this hydrogen layer maintain steady fusion, forming another layer of helium underneath. Helium fusion ignites when temperature rises to 100 million K. This causes the creation of carbon and heavier elements, generating a burst of X-ray energy that flows from the neutron stars.

What is an X-ray burster? Describe its activity.

Accretion disk is a rapidly rotating disk of material that gradually falls inwards as it orbits a white dwarf.

What is an accretion disk?

EDP is the pressure exerted by tightly packed electrons, unrelated to temperature

What is electron degeneracy pressure?

______________ ____________ is the process of making new generations of stars and gradually changing the chemical composition of the interstellar medium.

What is galactic recycling?

We observe pulsars as the neutron stars emit steady beams of light if they sweep past Earth

What is necessary for the neutron star to beam light?

Neutron degeneracy pressure is the pressure exerted by tightly packed neutrons, unrelated to temperature. This pressure acts against the crush of gravity.

What is neutron degeneracy pressure, and how does it prevent the star from collapsing?

_________ is the inseparable, four-dimensional combination of space and time.

What is spacetime?

The entire galaxy is about 100,000 light years in diameter.

What is the approximate diameter of our galaxy?

There have been observations of sudden changes in X-ray brightness thought to have come from energy released by matter being torn apart by the tidal forces of a possible black hole.

What is the evidence for a supermassive black hole at the center of our galaxy?

____________ is the process where the wavelength of electromagnetic radiation lengthening as it climbs out of a gravitational well due to gravity.

What is the gravitational redshift, and why does it happen?

______ ________ is the gas and dust that fills the space between stars in a galaxy. It resides in the galactic disk in the Milky Way galaxy.

What is the interstellar medium and where in our galaxy does it reside?

The limiting mass of a neutron star is 3 times the mass of the Sun.

What is the limiting mass of a neutron star?

__________ is the place at the center of a black hole where gravity crushes all matter to an infinitely tiny and dense point.

What is the singularity?

As the stars in a galaxy become older, the galaxy shifts from the blue cloud to the red sequence. All galaxies start as star-forming systems in the blue cloud. The merge of these galaxies make larger galaxies and some stop forming new stars. This causes galaxies to shift up and right to the red sequence.

What process is believed to cause the movement of a galaxy with time from the blue cloud to the red sequence?

When a white dwarf reaches 1.4 times the mass of the Sun limit, it explodes in a white dwarf supernova.

What process leads to a white dwarf supernova?

When a white dwarf reaches 1.4 times the mass of the Sun limit, it explodes in a white dwarf supernova. A white dwarfs mass reaching 1.4 times the mass of the Sun its temperature rises enough to allow carbon fusion. Carbon fusion ignites, causing the white dwarf to explode completely into a supernova

What process leads to a white dwarf supernova? What happens when the white dwarf's mass approaches the Chandrasekhar limit of 1.4 MSun? How much of the white dwarf is left after the supernova explosion?

Spiral arms produce the spiral structure in the disk of our galaxy.

What produces the spiral structure in the disk of our galaxy (also in other spiral galaxies)?

Spiral arms bear all the hallmarks of star formation and contain molecular clouds, which trigger star formation.

What triggers star formation in the spiral arms?

The evidence linking gamma-ray bursts to exploding stars was found through observing these events in different wavelengths of light.

What type of observation has tied the gamma ray bursts to hypernovae?

They orbit the Milky Way at distances of 160,000 and 200,000 light years. Sagittarius and Canis Major are galaxies closer to the Milky Way.

Where are The Large and Small Magellanic Clouds located?

Most galaxies in our local group are round and diskless like elliptical galaxies, but they are small and less bright so they fall into a subtype called dwarf spheroidal galaxy. Irregular galaxies are more commonly observed in distances because they were more common when the universe was younger and as the universe expanded they traveled great distances.

Which type of galaxy is most numerous in our Local Group? How do their masses compare with a typical globular cluster in our halo? What is a possible explanation for the observation that irregular galaxies more common at great distances in the universe?

Galaxies in the blue cloud contain numerous hot, young stars (active star formation), mostly spiral or irregular galaxies.

Which types of galaxies make up the blue cloud?

Galaxies in the red sequence contain only red, old stars, mostly elliptical galaxies.

Which types of galaxies make up the red sequence?

White dwarfs are primarily composed of helium.

White dwarfs are primarily composed of which element?

All pulsars must be neutron stars, because no other massive object can spin so fast.

Why are all pulsars neutron stars, but not all neutron stars pulsars?

Compression of clouds causes the formation of new stars that are mainly blue, making the spiral arms appear blue. The stars between the arms are red and old, creating the red patches.

Why are spiral arms blue in color with red patches?

Stars pass through spirals arms with little change in their orbits because they always remain too widely separated to collide with each other, whereas spiral density waves closely pack gas clouds, so the gravity within the clouds become strong enough to trigger cluster formation.

Why do stars pass through the spiral arms with little change in their orbits, but the clouds experience compression?

Neutron stars in close binary systems speed up because matter accreting onto the neutron star adds angular momentum, whereas single neutron stars slow down.

Why do the neutron stars in close binary systems speed up instead of slowing down as do single neutron stars?

The emission from most X ray binaries pulsates rapidly as the neutron star spins. However, while both pulsars tend to slow down with time, the pulsation rates of X ray binaries tend to accelerate, presumably because matter accreting onto the neutron star adds angular momentum. Some of these neutron stars rotate so fast that they pulsate every few thousandths of a second ( and are called millisecond pulsars.)

Why do the neutron stars in close binary systems speed up instead of slowing down as do single neutron stars? What physical process is happening here?

This difference of gas particle speeds removes orbital energy from the inner region and causes the gas to spiral inward and fall into the white dwarf.

Why does material lose orbital energy and eventually fall into the white dwarf?

The ________ disk contains a mix of old and young stars, but the halo population is only old stars because the halo does not contain cold, dense molecular clouds required for star formation.

Why does the galactic disk contain a mix of old and young stars, but the halo population is one of old stars?

The inner part of the accretion disk heats up because gravitational potential energy is converted into thermal energy.

Why does the inner part of the accretion disk heat up?

Material in the accretion disk move faster as it moves towards the white dwarf because gas in the inner region orbits faster than the gas in the outer region (Kepler's Laws).

Why does the material in an accretion disk orbit increasingly faster as it moves toward the white dwarf?

___________ have to be rapidly rotating because the pulsations of the neutron stars are a result of conservation of angular momentum

Why must pulsars be a rapidly rotating neutron star?

Wien's Law

Wien's Law tells us that objects of different temperature emit spectra that peak at different wavelengths. Hotter objects emit most of their radiation at shorter wavelengths; hence they will appear to be bluer.

Conservation of Energy

a principle stating that energy cannot be created or destroyed, but can be altered from one form to another.

Magnetic Fields

a region around a magnetic material or a moving electric charge within which the force of magnetism acts.

Pulsation/pulsating star

a type of variable star, the variation in brightness resulting from expansion and subsequent contraction of the star.

Irregular galaxies

appear neither disk-like nor rounded

According to Einstein, what we perceive as gravity arises from a ___________ of spacetime.

curvature

Kinetic Energy

energy that a body possesses by virtue of being in motion.

Radiative Energy

energy that travels by waves or particles, particularly electromagnetic radiation such as heat or x-rays. An example of radiant energy is the source of energy used in radiation therapy.

Spiral galaxies

flat white disks with yellowish bulges at the center. Disks filled with cool gas and dust with hotter ionized gas scattered in between. Display spiral arms. (ex. Milky Way galaxy)

Gravitational Force

force that attracts any objects w mass

Thermal Energy

internal energy of an object due to the kinetic energy of its atoms and/or molecules. The atoms and/or molecules of a hotter object have greater kinetic energy than those of a colder one, in the form of vibrational, rotational, or, in the case of a gas, translational motion.

Newton's Version of Kepler's 3rd Law

p= orbital period (earth years) a= separation distance (in A.U.) m1 + m2= sum of object masses (in solar masses, Msun)

Stefan-Boltzmann Law

statement that the total radiant heat energy emitted from a surface is proportional to the fourth power of its absolute temperature. ... The law applies only to blackbodies, theoretical surfaces that absorb all incident heat radiation.

Potential Energy

the energy possessed by a body by virtue of its position relative to others, stresses within itself, electric charge, and other factors.

Electromagnetic Spectrum

the entire range of wavelengths or frequencies of electromagnetic radiation extending from gamma rays to the longest radio waves and including visible light.

Orbital Energy

the specific orbital energy (or vis-viva energy) of two orbiting bodies is the constant sum of their mutual potential energy ( ) and their total kinetic energy ( ), divided by the reduced mass.