THE UNIVERSE FINAL

OBAFGKM

"Oh, Be A Fine Guy, Kiss Me." Surface temperatures of blue O spectrum are as high as 40,000 K, while red M spectrum have temps as low as 3000 K. Cool red stars are much more common.

What are starbursts?

- A starburst galaxy is transforming its gas into stars much more rapidly than a normal galaxy.

How do quasars let us study gas between the galaxies?

- Absorption lines in the spectra of quasars tell us about intergalactic clouds between those quasars and Earth.

How are quasars powered?

- Active galactic nuclei are very bright objects seen in the centers of some galaxies, and quasars are the most luminous type. - The only model that adequately explains the observations holds that supermassive black holes are the power source.

How did the early universe change with time?

- As the universe cooled, particle production stopped, leaving matter instead of antimatter. - Fusion turned remaining neutrons into helium. - Radiation traveled freely after formation of atoms.

Why is the darkness of the night sky evidence for the Big Bang?

- If the universe were eternal, unchanging, and everywhere the same, the entire night sky would be covered with stars. - The night sky is dark because we can see back to a time when there were no stars.

Do supermassive black holes really exist?

- Observations of stars and gas clouds orbiting at the centers of galaxies indicate that many galaxies, and perhaps all of them, have supermassive black holes.

Why do galaxies differ?

- Some of the differences between galaxies may arise from the conditions in their protogalactic clouds. - Collisions can play a major role because they can transform two spiral galaxies into an elliptical galaxy.

What were conditions like in the early universe?

- The early universe was so hot and so dense that radiation was constantly producing particle-antiparticle pairs and vice versa.

What key features of the universe are explained by inflation?

- The origin of structure, the smoothness of the universe on large scales, the nearly critical density of the universe. - Structure comes from inflated quantum ripples. - Observable universe became smooth before inflation, when it was very tiny. - Inflation flattened the curvature of space, bringing expansion rate into balance with the overall density of mass-energy.

Did inflation really occur?

- We can compare the structures we see in detailed observations of the microwave background with predictions for the "seeds" that should have been planted by inflation. - So far, our observations of the universe agree well with models in which inflation planted the "seeds."

About how many times larger is the Sun's surface temperature than the temperature of boiling water?

15.5 times hotter.

About how many times larger is the Sun's luminosity than the luminosity of one billion 100-Watt light bulbs?

3.8X10^16

A Barred Spiral Galaxie

A Barred Spiral Galaxy is a galaxy that's spiral arms appear to have a straight bar or stars cutting across the center, with spiral arms curling away from the ends of the bars.

What are carbon stars? How are they important to life?

A Carbon Star is a star whose atmosphere are especially carbon rich, thought to be near the end of their lives; carbon stars are the primary source of carbon in the universe. Carbon is the building block for life.

How does a galactic fountain help circulate new elements within the Milky Way?

A Galactic Fountain is a model for the cycling of gas in the Milky Way Galaxy in which fountains of hot, ionized gas rise from the disk into the halo and then cool and form clouds as they sink back into the disk.

Describe the mass, size, and density of a typical neutron star. What would happen if a neutron star came to your hometown?

A Neutron Star is a compact corpse of a high-mass star left over after a supernova; it typically contains a mass comparable to the mass of the Sun in a volume just a few kilometers in radius. A paperclip sized neutron would out way mount everest, plummeting through earth, to the other side, and continue drilling holes as it fell back and forth. If the whole star visited earth, the gravity would compares the entire ear into the size of a shell no thicker than your thumb.

What is a planetary nebula? What happens to the core of a star after a planetary nebula occurs?

A Planetary Nebula is the glowing cloud of gas ejected from a low-mass star at the end of its life, and lit up by the ultraviolet light from the stars core. After a few million years, the nebula will disappear, leaving behind a white dwarf.

What is a protostellar disk? Describe how such a disk enables additional matter to accrete onto the protostar.

A disk of fast moving material surrounding a prostar, transferring angular momentum away from the infalling gas, enabling the prostar to grow more massive. Additionally, as the disks molecules decrease in speed due to friction, the gas falls to the surface, adding to its mass.

What is a protostar? How does it form? Why does its mass increase with time?

A forming star that has not yet reached the point where sustained fusion can occur in its core. The gas that forms the prostar has contracted, and no longer supports the gas above it. This results in the gas above it raining down on the prostar, increasing its mass.

What are gamma-ray bursts, and how do we think they are produced?

A gamma-ray burst is a sudden burst of gamma rays from deep space; such bursts apparently come from distant galaxies in which extremely powerful supernova explosions form black holes, but their precise mechanism is unknown.

Which stars have longer lifetimes: massive stars or less massive stars? Explain why.

A massive star has more pressure> making it get hotter> the hotter it gets, the bigger the collisions between particle, the more likely fusion is to happen>more fusion means more energy>more energy means higher emissions of photons>more luminous. Also, the bigger the rate of fusion, the quicker its fuel runs out, thus shortening its life span, and making them more rare.

What is a molecular cloud? How does a molecular cloud compare with temperature and density with the rest of the interstellar medium?

A molecular cloud is an interstellar cloud that is particularly cold and dense, allowing atoms to combine together into molecules. The temperature of a molecular cloud is around 10 K to 30 K.

What evidence suggests that the Milky Way formed from the merger of smaller protogalactic clouds?

A protogalactic cloud is a huge, collapsing cloud of intergalactic gas from which an individual galaxy formed. The stars in the halo oif the Milky Way are very old, and have an H-R turn off point of 12 billion years. But there are still small traces of heavy elements in their stars. This means that they had to be formed from the remanence of another galaxy colliding with a protogalic cloud.

Globular Cluster

A spherically shaped cluster of up to a million or more stars; globular clusters are found primarily in the halos of galaxies and contain only very old stars.

What causes a white dwarf supernova? Observationally, how do we distinguish white dwarf and massive star supernovae?

A white dwarf supernova occurs when accretion disk and novas have left behind so much mass on the white nova that it reaches the white nova limit (greater than 1.4sm). This can also happen when ttwo binary white dwarf companions collide. When the mass of a supernova reaches >1.4sm, the degeneracy pressure van no longer support it, and the white dwarf becomes a super nova. White dwarf supernovas peak and then start to fade quicker than massive star supernovas.

Why do orbits of bulge stars bob up and down?

A. They're stuck to interstellar medium. B. Gravity of disk stars pulls them toward the disk. C. Halo stars knock them back into the disk. • The Sun's orbital motion (radius and velocity) tells us the mass within Sun's orbit: 1.0 ⋅ 1011MSun That is 1.9 ⋅ 1041kg! Or, 190,000,000,000,000,000,000,000,000,000,000,000,000,000 kg.

Where will the gas be in 1 trillion years?

A. blown out of galaxy B. still recycling just like now C. locked into white dwarfs and low-mass stars • We observe the star-gas-star cycle operating in Milky Way's disk using many different wavelengths of light. • 21-cm radio waves emitted by atomic hydrogen show where gas has cooled and settled into disk. • Radio waves from carbon monoxide (CO) show the locations of molecular clouds. • Long-wavelength infrared emission shows where young stars are heating dust grains. • Infrared light reveals stars whose visible light is blocked by gas clouds. • X rays are observed from hot gas above and below the Milky Way's disk.

What do we mean by a star's apparent and absolute magnitudes? How are they related to apparent brightness and luminosity?

Absolute Magnitude is the apparent brightness a star would have if it were 10 parsecs from earth. Thus, with a constant distance, they can calculate luminosity.

What are accretions disks, and why do we find them only in close binary systems? Explain how the accretion disk provides a white dwarf with a new source of energy that we can detect from Earth.

Accretion discs are formed when a main-sequence star that is in a binary star system with a white dwarf starts spilling material into white dwarf's orbit. Because of the white dwarfs high mass, and therefore large gravitational pull, the gas moves fast, creating friction, thus raising temperature. Hydrogen falls to the surface. The gravity creates a thin layer around the white dwarf made of hydrogen.l This hydrogen eventually heats, and starts fusion.

What do all low-mass stars have in common? Why do they differ in their levels of surface activity? What are flare stars?

All low mass stars have around the same life span, fuse the same, maintain equilibrium the same, transfer energy the same, and will die the same. They differ based on the depth of their convection zone. The cooler the interior, the deeper the convection zone, allowing for the flow of energy. Flare stars are small spectral type M stars that displays particularly strong flares on their surface due to the churning in their convection zone

How do we know that pulsars are neutron stars? Are all neutron stars also pulsars? Explain.

All pulsars are neutron stars, but not all neutron stars are pullsars. We know that pulsars are neutron stars becaus eno other object could spin fast enough to create that type of pulse. A pulsar is a neutron star from which we see rapid pulses of radiation as it rotates. It pulses at precise intervals of time. They are created when the sit in between two supernova remnants. As iron collapses in the core, the neutron star gains higher rotational speed. The colapse also bunches magnetic field lines tightly together, amplifying their strength, and shooting radiation out of the stars poles.

Describe the differences between normal spiral galaxies, barred spiral galaxies, and lenticular galaxies.

All spiral galaxies have disk and spheroidal components, however there are some variations: A Barred Spiral Galaxy is a galaxy that's spiral arms appear to have a straight bar or stars cutting across the center, with spiral arms curling away from the ends of the bars. LenticularGalaxies have disk and spheroidal components, but lack the spiral arms. They are sometimes classified as a mix between spiral and elliptical galaxies because they have less cool gas than spirals, but more cool gas than ehlipticals.

How are stars formed? What are star clusters?

All stars are born from giant gas clouds, that usually form several stars within close proximity to each other, called star clusters. All the stars in these clusters are about the same age, which makes them useful for comparing and contrasting differentiating characteristics among stars of the same age.

Why does the energy produced by fusion in the solar core take so long to reach the solar surface? Describe the processes by which energy generated by fusion makes its way to the Sun's surface.

Although photons created in the core travel at the speed of light, the path they take to the surface is not linear, but very zig-zagged.The solar interior is so dense that a photon can only go a millimeter without colliding with an electron. With each collision, the photon is deflected in a new a random direction, and thrussted into another electron, creating the zig zag path. This makes for a long journey to the surface.

Explain how the presence of a neutron star can make a close binary star system appear to us as an X-ray binary. Why do some of these systems appear to us as X-ray bursters?

An X-Ray binary is a binary star system that emits substantial amounts of X rays, thought to be from an accretion disk around a neutron star or black hole. Because gravity is so intense around a neutron star, the amount of gravitational potential energy of the accretion dick turns into thermal energy that is so hot, its emits X-rays.

What are ionization nebulae, and why are they found near hot, massive stars?

An ionization nebulae is a colorful, wispy cloud of gas that glows because neighboring hot stars irradiate it with ultraviolet photons that can ionize hydrogen atoms, causing a glow from atoms that have electrons in an excited state that then go down.

What do we mean by atomic hydrogen gas? How common is it, and how do we map its distribution in the galaxy?

Atomic Hydrogen Gas is gas composed mostly of hydrogen atoms, though in space it is generally mixed with helium and small amounts of other elements as well; it is the most common form of interstellar gas. Once hot bubbles or superbubbles cool, they become part of the atomic hydrogen gas. We can map the distruption of atomic hydrogen gas through radio waves, because it emits spectral lines with wave lengths of 21 centimeters.

Briefly summarize the different types of gas present in the disk of the galaxy, and describe how they appear when we view the galaxy in different wavelengths of light.

Atomic hydrogen Gas fills most of the galactic disk. Carbon monoxide shows us where the cold/dense molecular clouds reside, in the central narrow portion of the disk. Each element can be seen through their respective wavelengths. Using a telescope that takes in light at that specific wavelength, we can see the distribution of this gas throughout the universe.

Why does the H-R diagram of a globular cluster show a horizontal branch? What are the characteristics of the stars on the horizontal branch?

Because stars at the end of their life are fusing helium, which is why they spike up on the H-R diagram. They are becoming Red Giants.

Why are the chromosphere and corona best viewed with ultraviolet and X-ray telescopes, respectively? Briefly explain how we think the chromosphere and corona are heated.

Because the density of gas is so low in these areas, we cannot see visible light, except in total eclipses. Because X-Rays and Ultraviolet light are so prevalent in these areas, its best to observe them with x-ray and ultraviolet telescopes. We don't know exactly how these areas get so hot, but scientists believe that the same magnetic waves that prevent hot plasma from entering sun spots also carries energy into the corona and chromosphere, deposited as heat.

Describe some of the nuclear reactions that can occur in high-mass stars after they exhaust their core helium. Why does this continued nuclear fusion occur in high-mass stars but not in low-mass stars?

Because the pressure is so great in high mass stars, the core temperature is so high the it off set degeneracy pressure, allowing the core to expand and heat up, creating carbon fusion. Carbon fusion happens when carbon and helium interact to make elements like oxygen. Helium can react with oxygen to make neon, neon in magnesium, so on and so forth. These newly created elements fuse with each other to make other elements as well.

How do we know that spiral arms do not rotate like giant pinwheels? What makes spiral arms bright?

Because the stars all have about the same orbital speed, the stars close to the center have less distance to travel to complete one orbit, while the stars on the outside have much more distance. The less distance, the quicker they complete an orbit, and vice versa. The larger more luminous stars die quickly, and therefor never live long enough to leave the spiral that they were born in in. Therefore, these more luminous stars make the arms brighter.

What creates a bubble of hot, ionized gas? What happens to the gas in the bubble over time?

Bubbles are an expanding shell of hot, ionized gas driven by stellar winds or supernovae, with very hot and very low density gas inside. High speed gas ejected into space by a supernova or powerful stellar winds sweep up surrounding interstellar material, and create a bubble of hot, ionized gas. The particles in these are moving at nearly the speed of light, causeing radio waves as the electrons spiral around magnetic field lines.

Solar Flares

Bursts of X-Rays and fast moving particle ejected into space, created by changes in magnetic fields. Mostly seen occurring near sun spots.

Summarize each of the major links in the distance chain. Why are Cepheid variable stars so important? Why are white dwarf supernovae so useful, even though they are quite rare?

Cepheid variable stars, as well as white dwarf super novas, are all useful standard candle lights. We know that a white dwarf undergoes a supernova when its mass exceeds 1.4sm. Thus, knowing that all white dwarfs undergo a supernova at the same critical mass, we are able to determine that all white dwarfs have the same luminosity when they explode.

What are the six different layers of the sun, in order, from closest to farthest from the center.

Core Radiation zone Convection zone Photosphere Chromosphere Corona

What are cosmic rays? Where do they come from?

Cosmic Rays are particles such as electrons, protons, and atomic nuclei that zip through interstellar space at close to the speed of light when they are ejected from supernova.

How do we observe the life histories of galaxies?

Deep observations of the universe show us the history of galaxies because we are seeing galaxies as they were at different ages.

What is degeneracy pressure, and how does it differ from thermal pressure? Explain why degeneracy pressure can support a stellar core against gravity even when the core becomes very cold.

Degeneracy Pressure is a type of pressure unrelated to an objects temperature, which arises when electrons (electron degeneracy pressure) or neutrons (neutron degeneracy process) are packed tightly. Basically, there is no room for electrons to move, thus causing pressure that off sets the force of gravity like thermal energy. It differs from thermal energy because thermal energy depends on temperature, and degeneracy pressure depends only on density. I

What is degeneracy pressure, and how is it important to the existence of white dwarfs and neutron stars? What is the difference between electron degeneracy pressure and neutron degeneracy pressure?

Degeneracy Pressure is basically the pressure caused by particles resisting to get too close to each other. Quantum mechanics say that electrons (as well as neutrons) can only get so close to each other, so degeneracy pressure repels them away, stopping them from getting to close. This is how white dwarfs stay stable, and resist collapsing under the force of gravity without thermal pressure from nuclear fusion. If another force is stronger than the degeneracy pressure, the electrons are pushed so tightly together that they cannot exist freely, and they instantaneously disappear by combing with protons to form neutrons. This is electron degeneracy pressure. T Neutron degeneracy pressure is similar, but the pressure is much stronger.

How was the spectral sequence discovered, and why does it have the order OBAFGKM?

Discovered by female astronomers at Pickerning Observatory at Harvard. Flemmings started classifying starts based on their hydrogen lines. (A) had the strongest, and she worked her way down the alphabet till she go to (O) that had the weakest hydrogen lines. Later, Cannon realized that it was easier to classify the stars by temperature, rather than hydrogen lines that Flemming's had been doing. But the hydrogen lines did correspond to the temperature. Thus, she simplified it down to 8 letters OBAFGKM. Letters represent the amount hydrogen lines, while the order has to do with their temperature.

Parsec

Distance used in measuring parallax. A stellar paralax with and angle of 1/10 arcsecond has a distance of 10 parsecs. 1/100 has 100 parsecs distance.

How do spiral and elliptical galaxies differ in terms of the presence or absence of disk and spheroidal components? How does this difference explain the lack of hot, young stars in elliptical galaxies?

Elliptical galaxies differ from spiral galaxies mostly in that they only have a spheroidal component, but lack a significant disk component. With the lack of a disk, and therefor spiral arms, they have very little cool gas because they are not able to undergo star-gas-star cycles, which means little to no new star formation. With little star formation, and a small abundance of heavy elements, the stars that are formed are usually smaller in size, thus are older and live longer lives.

True or False?: Stars that begin their lives with the most mass live longer than less massive stars because it takes them a lot longer to use up their hydrogen fuel.

False, more massive stars are much more luminous than low mass stars and use up their hydrogen faster, even though they have more of it.

True or False?: Two stars that look very different must be made of different kinds of elements.

False, stars appear different due to their different ages and masses, not composition.

What do we mean by solar activity?

Features of the sun that change with time, occuring due to the suns convection movement and weather, including: Sunspots Solar Prominences Solar Flares Coronal Mass Ejections

What is the helium fusion reaction, and why does it require much higher temperatures than hydrogen fusion? Why will helium fusion in the Sun begin with a helium flash?

Fusion only happens when two nuclei come close enough together to overcome electromagnetic repulsion to fuse. Since helium has a greater charge than hydrogen, it repels one another more strongly, thus requiring greater speeds to collide and fuse. To achieve these high speeds, the core needs to heat up enough due to the hydrogen fusion of the core. Once it has, three helium particle collide to make one carbon particle. Since the mass of carbon is slightly smaller than the mass of three helium, some mass is converted into energy that is released. The suns helium fusion will begin with a Helium Flash because the inert helium temperature is too low to counteract gravity. Instead, degeneracy pressure will fight gravity, while helium fusion heats the core rapidly without it expanding. This causes the fusion rate to go through the roof and release a tremendous amount of energy into the core. The thermal pressure then surpasses degeneracy pressure, pushing back against gravity, and causing the core to expand.

Spiral Galaxy

Galaxies that look like flat white disks with yellowish bulges at their centers. The disks are filled with cool gas and dust, interspersed with hotter ionized gas, and usually display beautiful spiral arms.

Solar Prominences

Giant loops of magnetic feild arcs that trap hot gas, and create "rings of fire". They can rise to heights of more than 100,000 kilometers above the suns surface, and can last for days to weeks, until the magnetic fields weaken,

What two forces are balanced in gravitational equilibrium? What does it mean for the sun to be in energy balance?

Gravitational Equilibrium is the outward push of internal gas pressure and the inward pull of gravity that is always at a perfect equilibrium. The suns outward pressure precisely balanced the inward pull of gravity Energy Balance is the balance between the rate at which fusion releases energy in the sun's core, and the rate at which the Sun's surface radites this energy into space. Without Energy Balance, the balance between preasure and gravity would not remain steady, thus eliminating the possibility for Gravitational Equilibrium.

Why are eclipsing binaries so important to measuring masses of stars?

Half of all stars have a companion star of some kind, making a binary star system. We can only measure mass using Newton's version of Kepler's third law. This means we need two stars that are orbiting each other. Eclipsing Binaries happen on a plane, so it is easiest to measure their average orbital distance. All we need to do is measure the time in between each eclipse. We can also determine a star's radii based on the length of time of the eclipse.

What clues to our galaxy's history do halo stars hold?

Halo Stars: 0.02-0.2% heavy elements (O, Fe, ...), only old stars Disk Stars: 2% heavy elements, stars of all ages • Halo stars formed first, then stopped. • Disk stars formed later, kept forming.

In broad terms, explain how the life of a high-mass star differs from that of a low-mass star. How do intermediate-mass stars fit into this picture?

High mass stars lives start out much like low mass stars, but everything occurs much more rapidly. They develop quicker, live shorter, and have the capability of creating much heavier elements because of the crushing mass of its outer layers. When they finally exhaust all their ability to fuse into heavier elements, they dont just get rid of their outer layers, leaving a white dwarf like low mass stars. They will explode into a massive SUPERNOVA. intermediate-mass stars are similar to high mass, but they cannot fuse anything heavier than carbon, and therefore end their lives at this stage.

What are jets? Why do we think they are related to the protostar's rotation? How do they affect the cloud surrounding the protostar?

High-speed streams of gas ejected from a prostar into space. They are aligned with the disk's rotational axis, indicating they are related to angular mometum. They may be shooting out angualr motion into space, while pumping kinetic energy into the molecular cloud surrounding.

Explain how Hubble proved that the Andromeda Galaxy lies beyond the bounds of the Milky Way.

Hubble saw that there were individual stars within the Andromeda Galaxy, thus making it its own island outside the milky way. He then saw a district dimming and brightening of stars that happened over regular periods, which he marked as Cepheids. After comparing the brightening and dimming of the stars over several night, he was able to estimate their luminosity, and used the luminosity to determine the galaxy's distance.

Why do we think that supernovae should sometimes form black holes? What observational evidence supports the existence of black holes?

In super massive stars, when a super nova from a white dwarf occurs, it leaves behind a neutron star and a cloud of gas. If the material from that cloud lands on the neutron star, neutron degeneracy pressure may not be able to handle the force of gravity due to its increased mass, and it collapses again, forming a black hole.

Briefly describe how gravitational contraction generates energy. When was it important in the Sun's history? Explain.

In the late 1800's, scientist thought that the sun generated energy through gravitational contraction, where the the shrinking gas cloud converted gravitational potential energy of gas into thermal energy as the gas moves inward. This is how the sun became hot enough to start nuclear fusion within it's core, but not how it has sustained itself. If the sun were to sustain itself through gravitational concentration, its lifespan would only be 25 million years, which is younger than the earth.

What is the interstellar medium? What is its chemical composition, and how do we measure it?

Interstellar Medium is the gas and dust that fills the space between stars in galaxies. The chemical composition is about 70% hydrogen, 28% helium, and 2% heavier elements. We know this my measuring the absorption lines when a stellar cloud passes in front of a star.

Why can't iron be fused to release energy?

Iron has the lowest mass per nuclear particle of all the elements that it cannot release energy through fusion or fission. It builds up on the core still degeneracy pressure can no longer support it, and the star explodes in a massive supernove.

Why is a star's birth mass its most fundamental property?

It determines the rate of fusion in its core, thus effecting its surface temperature, luminosity and life span.

Does the Sun's fusion rate remain steady or vary wildly? Describe the feedback process that regulates the fusion rate.

It remains steady because of equilibrium caused be a shrinking and contracting core. If the fusion rate varies, or the temperature varies, the core expands or contracts to off set the distribution, therefore keeping the fusion rate the same, so that the amount of energy created is equal to the amount of energy the sun gives off on the surface (note that it takes hundreds of thousands of years for the energy to rise to the surface, which means that the rate always has to be the same.

How would you expect the lifetime of a massive star near the top of the main sequence to compare to the Sun's?

It would be much shorter

If a star was moved twice as far away, what would happen to it?

It would get four times as faint.

In what sense is a black hole like a hole in the observable universe? Define the event horizon and Schwarzschild radius, and describe the three basic properties of a black hole.

Its like a hole because when you enter it, you leave the region of the universe that we can observe with a telescope, and you never return. The event-horizon is the boundary that marks the point of no return(where the escape velocity equals the speed of light) between a black hole and the outside universe; events that happen within the event horizon cannot effect our observable universe. Schwarzschild radius is the measurement of the event horizon of the black hole, which is dependent upon its mass. For a black hole of 1sm, it would have a Schwarzschild of 3 kilometers. For a black hole of 100 sm, it would have a Schwarzschild radius of 300 kilometers. The three properties of a black hole are MASS, ELECTRIC CHARGE, and ANGULAR MOMENTUM.

How is the expansion of the surface of an inflating balloon similar to the expansion of the universe? Use the balloon analogy of explain why Hubble's constant is related to the age of the universe.

Its like the rubber of a balloon thats being expanded, but the air that surround the inside and outside of it is not part of the universe. As the balloon expands, the surface area grows, and objects get further from each other that are on the surface.

What is Hubble's Law? Explain what we mean when we say that Hubble's constant is between 21 and 23 kilometers per second per million light-years.

Its the mathematical expression of the idea that more distant galaxies move away from us faster: v = H × d, where v is a galaxy's speed away from us, d is its distance, and H is Hubble's constant. THE UNIVERSE IS EXPANDING.

Lenticular Galaxies

LenticularGalaxies have disk and spheroidal components, but lack the spiral arms. They are sometimes classified as a mix between spiral and elliptical galxies because they have less cool gas than spirals, but more cool gas than ehlipticals..

What do we mean by the lookback time to a distant galaxy? Briefly explain why lookback times are less ambiguous than distances when discussing objects very far away.

Lookback time is the amount of time since the light we see from a distant object was emitted. If an object has a lookback time of 400 million years, we are seeing it as it looked 400 million years ago. However, it doesnt give us the exact distance or location, because the universe is expanding, and the object was in a different place when it emitted light.

How do the numbers of low-mass stars compare with those of higher-mass stars in new star clusters?

Low-mass stars greatly outnumber high-mass stars in new clusters. For every star born with 10sm to 150sm, there are about 10 stars born between 2sm and 10 sm, 50 stars born with masses between .5sm and 2sm, and a few hundred with masses bellow .5sm.

Radiation zone

Made up of calm plasma, at a temperature of 10 million where energy moves outwards in photons of light and X rays trillions of times moire intense than visible light at the surface.

What happens to the thermal energy released into molecular clouds as gravity makes them contract? Why doesn't it build up and stop star formation?

Molecular clouds quickly get rid of the thermal energy that is created as a result of gravitational contraction. Collisions between gas molecules transforms thermal energy into photons that escape the cloud, thus keeping the temperature low as the cloud condenses.

How do the galaxy types found in clusters of galaxies differ from those in smaller groups and those of isolated galaxies?

Most galaxies in the universe are gravitationally bound together with neighboring galaxies. Spirals are found mostly in collections of galaxies called GROUPS, which can hold up to a dozen galaxies. In clusters, there are a few hundred galaxies that span over 10 million light years. Elliptical galaxies are more prevalent in clusters, making up 50% of the large galaxies in the central regions of clusters, and 15% of the large galaxies in the outer clusters.

In what ways are all stars similar? In what ways do they differ

Most stars are much similar to the Sun. They all form in great clouds of gas and dust, and start their lives with roughly the same chemical composition as the sun: 74% hydrogen, 24% helium, and 2% elements heavier than helium. However, stars do differ by size, age, brightness, and temperature.

Orbital Velocity Law

Mr = r v2/G • The orbital speed (v) and radius (r) of an object on a circular orbit around the galaxy tell us the mass (Mr) within that orbit.

What are neutrinos? What was the solar neutrino problem, and how was it solved?

Neutrinos are subatomic particles made by fusion. They rarely interact with other forms of matter, and can pass through almost anything. It would take a slab of lead a light year in diameter to stop a neutrino. Because neutrinos rarely interact with matter, its hard to observe/detect them. When technology wasn't advanced enough to capture a neutrino, scientist had a problem. They either didn't understand fusion, or the neutrinos were going missing. Once we detected them, we had proof of fusion. The nuclear fusion creates electron neutrinos, but detectors have been able to pick up the other two types of neutrinos as well. This means electron neutrinos changed on their way to earth, which tells us what activity is going on in the sun.

How can we use orbital properties to learn about the mass of the galaxy? What have we learned?

Newton's version of Kepler's Thrid law allows us to determine the mass of a relatively large object when we know the period and average distance of a much smaller object in orbit around it. We can use the Sun's orbital velocity and its average distance from the galactic center to determine the mass of our galaxy within the sun's orbit (this does not include the mass of stars/planets/etc outside the orbit). We find that the total mass within the sun's orbit of the galactic center is about 100 billion times greater than the mass of the sun. We have found that the orbital speed of stars closer and far from the galactic center is about the same, which means that the concentration of mass can not be in the center, but rather resides in the Halo. However, we can not see this matter, because it does not give off light. This is known as dark matter.

What is the difference between nuclear fission and nuclear fusion?

Nuclear Fission is the process of splitting an atomic nucleus. This is used in nuclear power plants. Nuclear Fusion is the process of fusing two or more small nuclei into one. This is the process that takes place in the sun.

Draw a sketch of a basic Hertzsprung-Russell (H-R) diagram. Label the main sequence, giants, supergiants, and white dwarfs. Where on this diagram do we find stars that are cool and dim? Cool and luminous? Hot and dim? Hot and luminous?

O- the blues- are the hottest and most luminous. B A F G K M- coolest and dimmest. Exceptions: White dwarfs- hot but dim Super Giants- very big, bright and luminous. Giants- A step below supergiants. slightly smaller and cooler and dimmer.

How do the abundances of elements support the Big Bang theory?

Observations of helium and other light elements agree with the predictions for fusion in the Big Bang theory.

What is the maximum mass of a star? What kind of pressure limits how massive a star can be?

Observations suggest the maximum mass is 150 sm, but reseachers claim to have found a 300sm star, but since its not a binary star system, we dont know for sure. Radiation pressure, which is caused by light, makes a star have a maximum mass.

Describe the final stages a protostar goes through before fusion begins in its core. How are these stages represented on life track?

Once a prostar has acquired a certain amount of mass, its core begins to heat up. At the same time, its gravitational contraction decreases as the thermal pressure increases. As its thermal preasure increases, it must start radiating away mnore of its energy to allow graviational contraction to heat up its core even more. After millions of year, the prostar's core heats up hot enough to undergoes nuclear fusion, gravtitational contraction halts, and its surface temperature steadily stays at 3000 K. COME BACK TO THIS TOO COMPLICATED WHEN DRUNK

Describe in general terms how open clusters and globular clusters differ in their numbers of stars, ages, and locations in the galaxy.

Open Clusters are smaller, several thousand stare and 30-light years wide. They are younger in age, and residing in the disk of the galaxy. Globular Clusters are densely packed, with millions of stars and a width of 60-150 light years. In its center, there are more thann 10,00 stars paacked into a space of only a few liught years. They are older in age, and found in the Halo of the universe

How do we study galaxy formation?

Our best models for galaxy formation assume that gravity made galaxies out of regions in the early universe that were slightly denser than their surroundings.

How do observations of the cosmic microwave background support the Big Bang theory?

Radiation left over from the Big Bang is now in the form of microwaves—the cosmic microwave background—which we can observe with a radio telescope.

What lies in the center of our galaxy?

Radio emission from center Swirling gas near center Orbiting stars near center • Stars appear to be orbiting something massive but invisible ... a black hole? • Orbits of stars indicate a mass of about 4 million MSun. • X-ray flares from galactic center suggest that tidal forces of suspected black hole occasionally tear apart chunks of matter about to fall in.

What is Sgr A*? What evidence suggests that it contains a massive black hole?

Sgr A* is a region of space (about the size of our solar system) where a few million stars orbit an object. Using Newton's version of keplers thir law, scientists have concluded that all the mass orbiting this object totals a mass of 4 million times the our sun, within the orbital region of our solar system An object that massive within such a small space, must be a black hole. We have observed burst of X-Ray flares from the place we suspect the black hole to be.

Suppose you are falling into a black hole. How will you perceive the passage of your own time? How will outside observers see time passing for you? Briefly explain why your trip into a stellar- time passing for you? Briefly explain why your trip into a stellar-mass black hole is likely to be lethal.

Spectators will see you slowing down in time as you get closer to the event horizon. As you get closer and closer, time will slow down so much that it will seem that you have stopped. Spectators will never see you cros the event horizon. But as the person falling in, you do not see a shift in time. It only takes a moment before you are sucked into oblivion, and spagetified under the immense force of gravity.

What are the three major types of galaxies, and how do their appearances differ?

Spiral Galaxies: Galaxies that look like flat white disks with yellowish bulges at their centers. The disks are filled with cool gas and dust, interspersed with hotter ionized gas, and usually display beautiful spiral arms. The stars of all different colors make these galaxies appear white. Elliptical Galaxies: Galaxies that appear rounded in shape, often longer in one direction, like a football. They have no disks and contain very little cool gas and dust compared to spiral galaxies, though they often contain very hot, ionized gas. Their old red stars make up their glow. Irregular Galaxies: Galaxies that look neither spiral nor elliptical.

What triggers star formation within a spiral arm? How do we think spiral arms are maintained?

Spiral arms are places within the disk where stars and gas clouds are more densely packed. When gas clouds collide and get more densely packed, they trigger star formation. When stars die, they trigger supernovas, which can lead to the formation of even more stars. Spiral arms are maintained through Spiral Density Waves- gravitationally driven waves of enhanced density that move through a spiral galaxy and are responsible for maintaining its spiral arms.

What do we mean by a standard candle? Explain how we can use standard candles to measure distances.

Standard Candle Light is the method we use to measure distance (when parallax angles aren't measurable) when we have some means of knowing the objects true luminosity, so that we can use its apparent brightness to determine its distance with the luminosity-distance formula.

What is the defining characteristic of a main-sequence star? Briefly explain why massive main sequence stars are more luminous and have hotter surfaces than less massive main-sequence stars.

Star's on the main sequence share a commonality between their mass, temperature, luminosity, and lifespan. Smaller stars are cooler, less bright, and have a longer lifespan, while larger mass stars are hotter, brighter, and short lived. This pattern shows us that mass is the most important attribute affecting the fusion within a star. A massive star has more pressure> making it get hotter> the hotter it gets, the bigger the collisions between particle, the more likely fusion is to happen>more fusion means more energy>more energy means higher emissions of photons>more luminous. Also, the bigger the rate of fusion, the quicker its fuel runs out, thus shortening its life span, and making them more rare.

Why do stars tend to form in clusters? Describe the process by which a single cloud gives birth to an entire cluster of stars.

Stars form in clusters because high mass clouds are most likely to have the right conditions for star formation. Thus, high mass clouds create clusters of stars. High-mass/high-density clouds have a higher presence of gravity, but are also full of enough turbulence and magnetic fields to resist gravity as it builds in size. Once it reaches a certain size, gravity take over, and rips the cloud into multiple segments that become star systems.

Describe the basic characteristics of stars' orbits in the bulge, disk, and halo of our galaxy.

Stars in the disk all orbit in roughly a circular motion all in the same direction on nearly the same plane. Stars in the bulge and halo soar high above and below the disk in randomly oriented orbits. They are all old stars, composed mostly of the basic helium and hydrogen elements.

Summarize some of the observational evidence supporting our ideas about how heavy elements form in massive stars?

Stellar spectra confirms this. Through absorption lines, we can see that older stars contain fewer heavier element than younger stars do. This confirms the theory on the orgins of the elements, because as stars have died over time, they have released heavier elements, which become parts on new stars.

Sunspots

Sun spots are about 4000 K, which is 1800 K cooler than the surface temperature. Magnetic fields prevent hot plasma from entering sun spots, thus keeping them cool.

Why do star clusters make superbubbles? What happens to those bubbles when they grow thicker than the galactic disk?

Superbubbles are essentially a giant interstellar bubble, formed when the shock waves of many individual bubbles merge to form a single giant shock wave. Because star clusters have stars about the same age, the biggest stars die around the same time, undergo supernovas, and combine their bubbles. When a bubble grows too large, the milky way disk cannot contain them. Once the bubble breaks out of the disk, nothing can slow its expansion, which causes it to have a blow out: a volcanic eruption on a galactic scale that shoots hot gas upwards into the galactic halo.

Apparent Brightness

The Apparent Brightness is the amount of power(energy per second) reaching us per unit squared. The Brightness of a star depends on distance, as well as how much light the star is generating.

What are the Large and Small Magellanic Clouds, and the Sagittarius and Canis Major Dwarfs?

The Large and Small Magellanic Clouds are small galaxies, at a distance of 150,000 and 200,000 light-years away, that orbit the milky way. Sagittarius and Canis Major Dwarfs are also small galaxies, but closer, that are on a collision course with the milky way. Our tidal forces will ultimately rip them apart.

What do we mean by a star's luminosity class? What does the luminosity class tell us about the star? Briefly explain how we classify stars by spectral type and luminosity class.

The Luminosity class tells us where the star lies on the HR diamgram CLASS DESPRITION I Supergiants II Bright Giants III Giants IV Subgiants V Main-sequence stars

What do we mean by the singularity of a black hole? How do we know that our current theories are inadequate to explain what happens at the singularity?

The Singularity of a black hole is at the center, where, in principle, gravity crushes all matter to an infinitely tiny and dense point. However, Relativity and Quantum Physics, both have different theories of what happens at the center of the black hole, and each is successful in explaining other laws that define a black hole. Because we cannot see past the event horizon, and can only use our understanding of these theories to theorizer what happens in a black hole, we will never know until these two theories are brought together to come to an agreed upon understanding.

What features of molecular clouds make the conditions favorable for star formation?

The abundance of hydrogen and helium that allows nuclear fusion to start when gravity contracts the cloud till it becomes hot. Molecular clouds are the only places in space where gravity can overcome the pressure of gass because of the high density. Because the cloud is cold, gravity doesn't have to overcome thermal pressure at first, and is able to compact the the gas dense enough to create a star.

How is a star's apparent brightness related to its luminosity? Describe the inverse square law of light.

The apparent brightness depends on the inverse square law. If you veiwed the sun from twice earths distance, it would appear 1/4 as bright. 100 times the distance= 1/10000 the brightness.

What is the cosmological horizon, and what determines how far away it lies?

The boundary of our observable universe, which is where the lookback time is equal to the age of the universe. Beyond this boundary in spacetime, we cannot see anything at all because this is beyond the birth of the universe. The universe was born roughly 14 billion years, so we cannot look back further than that time.

Spiral Arms

The bright, prominent arms, usually in a spiral pattern, found in most spiral galaxies

Bulge

The central portion of a spiral galaxy that is roughly spherical (or football shaped) and bulges above and below the plane of the galactic disk.

What will happen to Earth as the Sun changes in the future?

The climate regulation will eventually break down as the sun warms. Within a bilion to 4 billion years, the rising heat will caus ethe oceans to start evaporating, bring an end to life for organisms who havnt stored well protected water. In 5 billion years, when the sun exhausts its hydrogen suply, itll become a red giant and expand, becoming more lumionus, and rising the teperature of earth to over 1000 K.

When a star exhausts its core hydrogen fuel, the core contracts but the star as a whole expands. Why?

The core shrinks because it can't with stand the force of gravity against its decreasing thermal energy. However there is still a lot of hydrogen left surrounding the core. The pressure of gravity on this shell, as well as the core, heats it up hot enough for it to undergo hydrogen shell fusion around the core helium (product of hydrogen fusion). The fusion happens at a rate much fast than it had in its core as a main sequence star, that it creates a lot of thermal pressure, which causes the outer layers to expands to become luminous enough to give off the energy being created,

Distinguish between the disk component, and the spheroidal component of a spiral galaxy. Which component includes cool gas and active star formation?

The disk component is the portion of a spiral galaxy that looks like a disk and contains an interstellar medium with cool gas and dust; stars of many ages are found in the disk. The spheroidal component is the portion of any galaxy that is spherical (or football-like) in shape and contains very little cool gas; it generally contains only very old stars. Elliptical galaxies have only a spheroidal component, while spiral galaxies also have a disk component

Briefly describe the characteristics that distinguish the galaxy's disk population of stars from its spheroidal population of stars.

The disk population contains both young and old stars, all of which have heavy elements proportion of 2% like our sun. All these stars orbit on about the same plane, at about the same speed in a circular motion. Spheroidal population is made of stars that are all old, therefore making them smaller, which dont contain many heavy- elements. They sometimes can have masses made up of as little as .002% heavy element. They orbit within the bulge and halo in random direction, in an elliptical orbit.

What is a nova? Describe the process that creates a nova and what a nova looks like.

The dramatic brightening of a star that last a few weeks and subsides; occurs when a burst of hydrogen fusion ignites in a shell on the surface of an accelerating white dwarf in a binary system.

Why do we think the very first stars were much more massive than the Sun?

The first stars must have been made of only helium and hydrogen, because the abundance of heavy elements has come through the birth and death of stars. These other elements help the formation of stars today, by allowing thermal energy to morph into photons. But before those elements, the clouds were hotter, which meant that it was harder for gravity to overcome thermal pressure. The only way stars could form were in massive and dense molecular clouds which would have formed massive stars. Once they died, they created heavier elements, which became part of the interstellar medium.

Why do we need to understand the evolution of the universe in order to understand the lives of galaxies?

The galaxies relatively close by are about the same age as our Milky Way. If we want to see younger galaxies to see how they formed, we need to look at galaxies billions of light years away. The further we look into the distance, the further we look in time, which means we are looking at galaxies in their youngest stages when the universe was young as well.

What is interstellar medium made of?

The gas is made mostly of hydrogen and helium, the only elements produced during the Big Bang. This means the first stars must have been made from clouds only of hydrogen and helium. As time went on, stars started to turn hydrogen and helium into heavier elements, which becomes the dust of various elements in the interstellar medium. We can measure the composition when a interstellar cloud pass in front of a star, allowing scientists to examine the absorption lines. This absorption lines have specifc wavelengths, which give us a composition of the elements that make up the cloud.

Why does nuclear fusion require high temperatures and pressures?

The high temperature causes the nuclei to move at high speeds, allowing them to get close enough to fuse. The higher the temp, the harder the collisions, the more likely nuclear fusion will occur. The high pressure of the overly layer keep the plasma in the radiation zone stable. Without the high pressure, the plasma would explode into space.

How does the fusion of helium in the core of a red giant occur?

The hydrogen fusion shell creates more helium, the core rises in mass, and gravitational contraction shrinks it down, which makes it much denser and hotter. This rise in temperature at the core, cause a rise in the rate of fusion in the surrounding shell, which outputs more and more helium, adding to the cores mass. With no equilibrium, this process continues until the core heats up to 100 million K. At this point, helium nuclei are able to fuse together.

What is the Cosmological Principle, and how is it important to our understanding of the universe?

The idea that matter is distributed uniformly throughout the universe on very large scales, meaning that the universe has neither a center nor an edge. This means the universe is not expanding into anything. Its like the rubber of a balloon thats being expanded, but the air that surround the inside and outside of it is not part of the universe.

Coronal Mass Ejections

The large number of fast moving particles ejected during solar storms and flares that move in magnetic feild bubbles, sometimes towards earth, that can hamper radio transmissions, disrupt electrical power delivery, and damage electronic components in satellites.

Why is mass so important to a star's life? How and why do we divide stars into groups by mass?

The mass of a star determines its lifespan, rate of fusion, temperature, luminosity, apparent brightness, and its place on the H-R diagram, as well as the way in which it will die; smaller stars leave behind white dwarfs, while larger stars die violently and leave behind neutron stars of black holes. Scientists divide the stars into three groups of masses: Low-mass Stars- stars born with less than about 2 solar mass of material Intermediate-mass stars: born with masses between 2 and 8 sm. High-mass stars- born with mass greater than 8sm.

Describe the leading model for explaining the sunspot cycle. Does the sunspot cycle influence Earth's climate? Explain.

The maunder minimum created abnormally low temperature in Europe, known as the mini ice age.

Chromosphere

The middle layer of the solar atmosphere, between corona and photosphere. Temperature of about 10,000 K. This region emits the most ultraviolet light.

What is the minimum mass for a star, and why can't objects with lower masses be true stars? What is a brown dwarf?

The minimum mass for a star to have a stable fusion core (where rate of energy release from surface equals rate of creation of energy through fusion in the core) is .08 solar masses. This is the smallest a star can be for the pressure to cause nuclear fusion in its core. A BROWN DWARF is a star thats mass is less than .08 sm, where the contraction stops, and the star gradually cools down with no nuclear fusion in its core.

What happens to a low-mass star after it exhausts its core helium? Why can't it fuse carbon into heavier elements?

The now carbon core will once again shrink under the pressure of gravity. The outer layer will expand once again, as it did as a red giant. Now we are left with a carbon core, a helium shell, and hydrogen shell. As the the hydrogen shell undergoes fusion, it heats up the helium shell to undergo fusion. In low mass stars, the degeneracy pressure will halt the collapse of the core before it gets hot enough to reach the 600 million k temperature it needs for carbon fusion.

Corona

The outer layer,extending several million kilometers above the visible surface. The region that emits the most x-rays because of its astronomically high temperature of 1 million Kelvin. However, its density is so low that objects in it would absorb relatively little heat despite its 1 mill K temp.

What is the sunspot cycle? Why is it sometimes described as an 11-year cycle and sometimes as a 22-year cycle? Are there longer-term changes in solar activity?

The period of about 11 years over which the number of sun spots rises and falls. There are solar maximum, where there are many sun spots, and solar minimums where there are few. The average amount of time between the peak of one solar maximum to another is about 11 years, but they have been seen as small as 7 years and as big as 15 years. At the solar maximum, the magnetic polls switch. 22 years is the suns complete magnetic cycle, where the polls flip, then flip again to the way it started. There have been rare occasions where this pattern is not true, like during the period between 1645 and 1715, the Maunder minimum, where there were no sun spots.

What event initiates a supernova? Explain what happens during the explosion and why a neutron star or a black hole is left behind. What observational evidence supports our understanding of supernova?

The pile up of pressure over powers the degeneracy pressure that was supporting the core. The electrons are pushed so tightly together that they cannot existy freely. in an instant they dispaer by combing with protons to form neutrons. With no electrons, there is no degeneracy pressure, which means gravity has full effect. The iron ball collapses into a ball of neutrons thats incredibly dense. The collapse halts because the neutrons have degeneracy pressure of their own. The collapse, however, release an enormas amount of energy, which is called a supoernova, scattering the outer layers into space. We are now left with just an incredibly dense neutron star. If the remaining mass of the neutron star is large enough, it can also overcome neutron degeneracy pressure, collapsing into the formation of a black hole. The evidence for these neutrino stars is the larger nebulas we can see as a result of their supernovas, that have spinning white neutrino stars at their core.

Disk

The portion of a spiral galaxy that looks like a disk and contains an interstellar medium with cool gas and dust; stars of many ages are found in the disk.

What do we mean by a cosmological redshift? How does our interpretation of a distant galaxy's redshift differ if we think of it as a cosmological redshift rather than as a Doppler shift?

The redshift we see from distant galaxies, caused by the fact that expansion of the universe stretches all the photons within it to longer, redder wavelengths. We use cosmological redshift because with further objects on the edge of of the cosmological horizon, distance and therefore speed are ambiguous.

Describe the mass, size, and density of a typical white dwarf. How does the size of a white dwarf depend on its mass?

The size, mass, and density of a white dwarf depends on its birth mass, and the elements it created while it was a star. For our sun, it would be mostly made of carbon. But low mass stars could not create carbon, so they end up as helium white dwarfs. Intermediate white dwarfs make heavier elements and are composed of oxygen and carbon etc. The more massive white dwarfs are actually smaller in size. Because they have more matter, they have a stronger gravitational contraction, which shrinks them down and makes them much more dense.

Core

The source of the Sun's energy where nuclear fusion occurs, transforming hydrogen into helium, with a temperature of 15 million K. The preasure here is 200 billion times greater than earth's atmosphere, and its mass density is 100 times that of water. The energy produced takes a few hundred thousand years to reach the surface after its been created.

What happens to the electron speeds in a more massive white dwarf, and how does this behavior lead to a limit on the mass of a white dwarf? What is the white dwarf limit?

The speed of electrons are much higher in massive white dwarfs. At a size of 1.4 solar masses, elctrons would start moving at the speed of light. Because no matter can surpass the speed of light, a white dwarf can not exced 1.4 solar masses. This is the White Dwarf Limit.

Halo

The spherical region surrounding the disk of a spiral galaxy.

Summarize the star-gas-star cycle shown in Figure 19.3

The star-gas-star cycle is the process of galactic recycling in which stars expel gas into space, where it mixes with the interstellar medium and eventually forms new stars. 1. Stars form from molecular clouds. 2. stars undergo fusion 3. stars die, explode, and return gas and new elements into interstellar space. 4. Supernova's turn into gas bubble and superbubbles of hot, ionized gas. These bubbles expand, and burst out of the disk. 5. The gas cools in the halo, and returns to the disk, adding to the atomic hydrogen clouds. 6. These clouds add new material and elements to the molecular clouds, which make stars.

About how many times larger is the Sun's radius compared to the Earth's radius?

The sun has a radius 100 times larger than that of earth.

About how many times larger is the Sun's mass than the mass of all the planets combined?

The sun is 1000 times larger in mass.

Photosphere

The visible surface of the sun, around 5,800 K. Much less dense than earths atmosphere. This is where sun spots reside, regions of intense magnetic fields.

How do giants and supergiants differ from main-sequence stars?

They don't generate energy through the fusion of hydrogen and helium. They have already exhausted their supply of hydrogen fuel in their core. Giants and Super Giants are massive stars that are cooler but much more luminous than our sun.

Describe the Algol paradox and its resolution. Why can the lives of close binary stars differ from those of single stars?

This binary star system has one star at 3.8sm and one at .8sm. They were born at the same time. More massive stars live shorter lives, but in this scenario, the 3.8sm star is still fusing hydrogen on the main sequence, while the .8m star is a sub-giant. This happened because when the sub-giant started to expand, part of its surface expanded into the other stars gravitational pull, and spilled into it. This is called mass exchange. So, the .8sm star use to be bigger, but during its expantion and orbit around its companion, a lot of its mass spilled into the other star.

In binary stars, the orbital period depends on the masses of the stars and the sizes of their orbits. Why is this so valuable to know?

This is the main way we determine the masses of stars.

What is interstellar dust? How does it interact with visible light? What are the consequences for our view of the heavens, and how is that view different in infrared light?

Tiny solid flecks of carbon, silicon, oxygen, and iron minerals found in cool interstellar clouds; they resemble particles of smoke and form in the winds of a red giant. These particles, that make up only 2% of interstellar clouds, absorb or deflect almost all the light that passes through the cloud, making the sky appear dark. Stars on the edge of these clouds appear redder because of the absporption of certain spectrums of light. This is known as interstellar reddening. We can view stars behind these clouds using in infared observatiuon because infered light passes through these clouds.

Convection zone

Turbulent region of sun with the most movement where the energy generated in the solar core pushes hot gas upwards, while cool gas cascades downwards.

What are the three basic types of binary star systems?

Visual Binary: A pair of stars we can distinctly see orbit each other. Sometimes we only see a single star shifting positions because its companion is too dim to see. Spectroscopic Binary: Identified through doppler shifts in spectral lines. Stars that move closer to each other will have a blue and red shift effected by its companion. Eclipsing Binary: A pair of stars that orbit in our plane of sight. When they are seperate, we see two distinct stars. When one sun eclipses the other, the apparent brightness goes down as it blocks light from the other star.

What do we mean by a star's spectral type, and how is spectral type related to surface temperature and color? Which stars are hottest and coolest in the spectral sequence OBAFGKM?

We can determine a stars temperature based on its color or spectral type. Cooler stars look red, hotter stars look blue. Stars in the middle, like our Sun, look yellowish orange.

How are the luminosities of galaxies related to their colors?

We can plot all the galaxies we can observe on a diagram similar to the H-R of stars. This diagram has color on the horizontal axis, and luminosity on the vertical axis. This diagram shows us that the old red elliptical galaxies tend to be the most luminous in the galaxy, while the young white/blue spiral and irregular galaxies tend to be the least luminous.

Explain how mathematical models allow us to predict conditions inside the Sun. How can we be confident that the models are on the right track.

We can take mathematical equations based on the laws of physics and the observations we have made to in relation to equations that explain/prove the theories. Because the equations are based on our knowledge of proven physics, they can be accurately tested on earth to prove the validity.

How do we use stellar parallax to determine a star's distance, and how can we then determine its luminosity?

We determine a distance based on the angle we observe through parallax shifts, which takes 6 months (observations are made from opposite sides of the sun to determine the angle). Once we know the distance, and since we can always measure the apparent brightness of a star from earth, we can plug it into the inverse square law, and calculate the stars luminosity.

Briefly explain how we can learn about the lives of stars, even through their lives are far longer than human lives?

We have snapshots of stars, old and young. By looking at the differences, and more importantly commonalities, we are able to understand the stellar world much more. In observing varius stars, luminosity, surface temperature, and mass are all fundemental in understanding their orgins. We can get these through the same calculations we use for the sun.

Explain why H-R diagrams look different for star clusters of different ages. How does the location of the main-sequence turn-off point tell us the age of the star cluster?

We know their age because we can plot their stars on and H-R diagram. The exact point where these clusters diverge from the HR diagram is called the main-sequence turn-off point. The age of these clusters is equal to the lifetimes of the star at its main-sequence turn-off point.

What are white dwarfs?

When a giant super star eventually runs out of fuel, it ejects its outer layer, and is left with a dead core, which is the White Dwarf.

How does the luminosity of a pulsating variable star change with time?

When a stars rate of fusion is not in balance with the amount of energy it gives off on the surface. This causes the star to expand and contract ion size, and fluctuates its temperature, thus making it more luminous at certain points in time, and less luminous in others.

What happens to a contracting cloud when its thermal energy can no longer escape the cloud's interior in the form of photons? How does the trapped thermal energy affect the process of star formation?

When photons can no longer escape, they get absorbed, and are left in an excited state. The collision of excited particles raises turns them back into thermal energy, which prevents it from escaping the cloud, and raises the temperature of the core. Once the temperature raises, so does the thermal pressure, which pushes against gravity and halts the gravitational contraction

Luminosity

When we talk about the brightness of a star in an absolute sense, that is regardless of their distance, we are talking about luminosity; the total amount of power that a star emits into space.

Stars spend about 90% of their life

as main-sequence stars.

23. What would stars be like if hydrogen, rather than iron, had the lowest mass per nuclear particle? a) Stars would rapidly burn all their hydrogen and have very short lifetimes. b) Nuclear fusion would be impossible so stars would slowly cool and dim after their initial formation. c) Nuclear fission would be impossible and elements heavier than iron would not exist. d) Stars would continue burning heavier and heavier elements and the universe would have far more lead and uranium. e) Stars would be much less dense, and therefore larger, but otherwise the same.

b) Nuclear fusion would be impossible so stars would slowly cool and dim after their initial formation.

24. Why are supernovas important to galactic ecology? a) They recycle material from stars that have died. b) They create new elements and blow them out into space so that new generations of stars can be made from them. c) They destroy elements, letting each new generation of stars begin anew.

b) They create new elements and blow them out into space so that new generations of stars can be made from them.

Inverse Square Law (Apparent Brightness Equation)

b= Apparent Brightness L= Luminosity r= distance

20. After the Sun becomes a red giant star and makes carbon in its core, why will it not make heavier elements? a) It will have run out of fuel. b) It will be near the end of its life. c) It will not be hot enough for further reactions to occur. d) The heavier elements will all go into a planetary nebula. e) A and B

c) It will not be hot enough for further reactions to occur.

22. Suppose the universe contained only low-mass stars. Would elements heavier than carbon exist? a) Yes, all stars create heavier elements than carbon when they become a supernova. b) Yes, but there would be far fewer heavier elements because high-mass stars form elements like iron far more prolifically than low-mass stars. c) No, the core temperatures of low-mass stars are too low to fuse other nuclei to carbon, so it would be the heaviest element. d) No, heavy elements created at the cores of low-mass stars would be locked away for billions of years. e) No, fission reactions would break down all elements heavier than carbon.

c) No, the core temperatures of low-mass stars are too low to fuse other nuclei to carbon, so it would be the heaviest element.

How can you tell the temperatures of stars?

color-the hottest stars are "bluish white" & spectral type

19. What happens to nuclear fusion when the hydrogen in a star's core runs low? a) it stops b) it shifts from the core to a shell around the core c) other elements start to fuse d) the star goes out of balance and becomes a red giant e) B and D

e) B and D

21. How does the life of a high mass star differ from the Sun's life? a) It forms much faster. b) It lives a shorter time on the main sequence. c) It makes elements heavier than carbon. d) It dies in a tremendous supernova explosion. e) all of the above

e) all of the above

Spectral Lines

isolated dark or bright lines in a spectrum produced by emission or absorption of light of a single wavelength. These lines occur when a sun has ionized elements (which occur at high tmeperatures) or molecules (indicating lower temperatures). These lines help determine the surface temperature.

When does a star leave the main sequence? a) after a few million years b) after a few billion years c) it depends on its mass d) when the hydrogen fuel in its core is used up e) C and D

it depends on its mass

To measure a star's luminosity, you need to know

its apparent brightness and distance

Because low mass stars have convective outer layers, a) they have surface activity similar to the Sun's. b) they can have starspots like the Sun's sunspots. c) they can have flares and emit X-rays. d) all of the above e) A and B

they have surface activity similar to the Sun's. they can have starspots like the Sun's sunspots. they can have flares and emit X-rays.

What does our galaxy look like?

• Dusty gas clouds obscure our view because they absorb visible light. • This is the interstellar medium that makes new star systems. • We see our galaxy edge-on. • Primary features: disk, bulge, halo, globular clusters • If we could view the Milky Way from above the disk, we would see its spiral arms.

Where do stars tend to form in our galaxy?

• Ionization nebulae are found around short-lived high-mass stars, signifying active star formation. • Reflection nebulae scatter the light from stars • Why do reflection nebulae look bluer than the nearby stars? • For the same reason that our sky is blue! Halo: no ionization nebulae, no blue stars ⇒ no star formation Disk: ionization nebulae, blue stars ⇒ star formation • Much of the star formation in the disk happens in the spiral arms. • Spiral arms are waves of star formation. Spiral arms are waves of star formation. 1. Gas clouds get squeezed as they move into spiral arms. 2. Squeezing of clouds triggers star formation. 3. Young stars flow out of spiral arms.

How did our galaxy form?

• Our galaxy formed from a cloud of intergalactic gas. • Halo stars formed first as gravity caused gas to contract. • Remaining gas settled into a spinning disk. • Stars continuously form in disk as galaxy grows older.

How is gas recycled in our galaxy?

• Star-gas-star cycle • Recycles gas from old stars into new star systems. • hot bubbles → atomic hydrogen clouds → molecular clouds → star formation → nuclear fusion in stars → returning gas → hot bubbles → atomic hydrogen clouds → ... • High-mass stars have strong stellar winds that blow bubbles of hot gas. • Lower mass stars return gas to interstellar space through stellar winds and planetary nebulae. • X rays from hot gas in supernova remnants reveal newly made heavy elements. • A supernova remnant cools and begins to emit visible light as it expands. • New elements made by a supernova mix into the interstellar medium. • Radio emission in supernova remnants is from particles accelerated to near light speed. • Cosmic rays probably come from supernovae. • Multiple supernovae create huge hot bubbles that can blow out of the disk. • Gas clouds cooling in the halo can rain back down on the disk. • Atomic hydrogen gas forms as hot gas cools, allowing electrons to join with protons. • Molecular clouds form next, after gas cools enough to allow atoms to combine into molecules. • Molecular clouds in Orion • Composition: - Mostly H2 - About 28% He - About 1% CO - Many other molecules • Gravity forms stars out of the gas in molecular clouds, completing the star-gas-star cycle. • Radiation from newly formed stars is eroding these starforming clouds.

How do stars orbit in our galaxy?

• Stars in the disk all orbit in the same direction with a little up-and-down motion. • Orbits of stars in the bulge and halo have random orientations.

Summary of Galactic Recycling

• Stars make new elements by fusion. • Dying stars expel gas and new elements, producing hot bubbles (~106 K). • Hot gas cools, allowing atomic hydrogen clouds to form (~100-10,000 K). • Further cooling permits molecules to form, making molecular clouds (~30 K). • Gravity forms new stars (and planets) in molecular clouds.