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Astr. 101 Test 3
Chapters 8,9 & 10
| Question | Answer |
|---|---|
| (The Sun) Nuclear Fusion of hydrogen into helium occurs in the _________. | Core |
| (The Sun) Energy moves through the Sun's __________ by means of the rising hot gas and falling of cooler gas. | Convection Zone |
| (The Sun) Nearly all the visible light we see from the sun is emitted from the _________. | Photosphere |
| (The Sun) Most of the Sun's ultraviolet light is emitted from the narrow layer called the _________ where temperature increases with altitude. | Chromosphere |
| (The Sun) We see the Sun's ______ most easily during total solar eclipse's. | Corona |
| (The Sun) The _____________ is the layer of the Sun between its core and convection zone. | Radiation zone |
| Which of the following changes would cause the fusion rate in the Sun’s core to increase? | An increase in the core temperature increases the fusion rate because the fusion rate is very sensitive to temperature. A decrease in the core radius causes the core to heat up and increase in density, which therefore leads to an increased fusion rate. |
| Suppose you could somehow start nuclear fusion in a box that stayed the same size. Increasing the fusion rate would cause the temperature inside the box to _____. | Increase. |
| What equilibrium for the core of a star means | The core of a star is in equilibrium when its temperature, size, and the rate of nuclear fusion all hold steady. |
| If you heat up a balloon, what happens to it? | The gas particles inside it move faster, causing it to expand until it stabilizes at a new, larger size |
| How the fusion rate is represented | The fusion rate is higher when particles combine together more frequently. In this animation fusion is represented by two particles combining together and a flash of light, and the fusion rate is represented by the height of the bar graph. |
| Which of the following must occur for a star’s core to reach equilibrium after an initial change in fusion rate? | If the fusion rate initially increases, then the core expands. If the fusion rate initially decreases, then the core contracts. |
| The Sun’s photosphere is __________. | the visible surface of the Sun |
| The word corona, as in the Sun’s corona, means _____ | The corona is the “crown” of the Sun, meaning it sits above all other layers of the Sun. |
| How does the density of Earth’s atmosphere change with altitude? As you go upward in altitude through Earth’s atmosphere __________. | the density steadily decreases |
| How do we observe different layers of the Sun’s atmosphere? | We use visible-light telescopes to observe the photosphere, ultraviolet telescopes to observe the chromosphere, and X-ray telescopes to observe the corona. |
| When we observe the Sun with an X-ray telescope, we see the _____. | The corona is the only layer of the Sun’s atmosphere hot enough to emit X rays. Now, remember that hotter objects emit higher-energy radiation, |
| The layer of the Sun’s atmosphere that is best observed with an ultraviolet telescope is the _____. | (The chromosphere) is hot enough to emit ultraviolet light but not hot enough to emit X rays. |
| Before we can use parallax to measure the distance to a nearby star, we first need to know __________. | The Earth-Sun Distance |
| Which of the following is a valid way of demonstrating parallax for yourself? | Hold up your hand in front of your face and alternately close your left and right eyes. |
| What is the cause of stellar parallax? | Stellar Parallax is caused by the Earths orbit around the sun. |
| The more distant a star, the __________. | the smaller its parallax angle. |
| Approximately what is the parallax angle of a star that is 20 light-years away? | 0.16 arcseconds Suppose a star's parallax is 0.1 arc-seconds. How far away is it? Use the formula D=1/p Plug in for p the value 0.1 arc-seconds Thus, D=1/0.01 = 10 parsecs The star is therefore 10 parsecs away from us. |
| Suppose that a star had a parallax angle of exactly 1 arcsecond. Approximately how far away would it be, in light-years? | 3.3 Light Years. |
| Which of the following is the best answer to the question, "Why does the Sun shine?" | As the Sun was forming, gravitational contraction increased the Sun's temperature until the core become hot enough for nuclear fusion, which ever since has generated the heat that makes the Sun shine. |
| Which of the following best describes why the Sun emits most of its energy in the form of visible light? | Like all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, and the Sun's surface temperature is just right for emitting mostly visible light. |
| Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is ________. | are converted to an amount of energy equal to 4 million tons times the speed of light squared |
| Sunspots are cooler than the surrounding gas in the photosphere because | strong magnetic fields slow convection and prevent hot plasma from entering the region. |
| What do sunspots, solar prominences, and solar flares all have in common? | They are all strongly influenced by magnetic fields on the Sun. |
| If the star Alpha Centauri were moved to a distance 10 times farther than it is now, its parallax angle would | Get Smaller. |
| Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore: | Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A. |
| What do we need to measure in order to determine a star's luminosity? | apparent brightness and distance |
| The total amount of power (in watts, for example) that a star radiates into space is called its _______ | Luminosity |
| What two pieces of information would you need in order to measure the masses of stars in an eclipsing binary system? | The time between eclipses and the average distance between the stars |
| Compared to a main-sequence star with a short lifetime, a main-sequence star with a long lifetime is __________. | less luminous, cooler, smaller, and less massive |
| Compared to a high-luminosity main-sequence star, stars in the upper right of the H-R diagram are __________. | cooler and larger in radius |
| Compared to a low-luminosity main-sequence star, stars in the lower left of the H-R diagram are __________. | hotter and smaller in radius |
| Which of these stars is the most massive? a) a main-sequence A star b) a main-sequence G star c) a main-sequence M star | A Main sequence star.The mnemonic "Oh be a fine girl kiss me".The letters from hottest (therefore most massive) to coolest. A comes before G, which comes before M. So generally, A stars are more massive than G stars, which are more massive than M stars |
| Which of these stars has the longest lifetime? a) a main-sequence A star b) a main-sequence G star c) a main-sequence M star | The colder the star, the longest lived. Hottest are O, coldest are M (here is, again, the order): O B A F G K M with M being the coldest, so those are the longest living ones. |
| We have confidence that the model is correct because it agrees with the observed characteristics of the Sun. Which of the following observations can be used to check that we really do know the Sun’s internal fusion rate? | Measurements of the Sun’s total energy output into space, and Observations of neutrinos coming from the Sun. |
| what is a star clusters that is the oldest? | a cluster whose brightest main-sequence stars are yellow |
| The age of stars in a cluster can be determined by | determining the main sequence turnoff point. in the H-R diagram |
| You observe a star cluster with a main-sequence turn-off point at spectral type G2 (the same spectral type as the Sun). What is the age of this star cluster? | 10 billion years. |
| Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do? | Calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity |
| Carbon fusion occur in high-mass stars but not in low-mass stars because ________. | the cores of low-mass stars never get hot enough for carbon fusion |
| What kind of gas cloud is most likely to give birth to stars? | a cold, dense gas cloud |
| The following figures show various stages during the life of a star with the same mass as the Sun. Rank the stages based on when they occur, from first to last | A one-solar-mass star spends about ten billion years as a hydrogen-burning main-sequence star, making this by far the longest stage of its life. 1. Cloud of dust, 2. Protostar, 3. main sequence star, 4. Red Giant, 5. Planetary Nebula, 6. White Dwarf. |
| Provided following are various elements that can be produced during fusion in the core of a high mass main sequence star. Rank these elements based on when they are produced, from first to last. | 1. Helium, 2. Carbon, 3. Oxygen, 4. Iron |
| High mass stars:- | *late in life fuse carbon into heavier elements *end life as a supernova *have higher fusion rate during main sequence life |
| Low mass stars:- | *The sun is an example *Final corpse is a white dwarf *have longer lifetimes *end life as planetary nebula |
| What happens when a main-sequence star exhausts its core hydrogen fuel supply? | The core shrinks while the rest of the star expands. |
| Why is iron significant to understanding how a supernova occurs? | Iron cannot release energy either by fission or fusion. |
| Algol consists of a 3.7 M Sun main-sequence star and a 0.8 M Sun subgiant. Why does this seem surprising, at least at first? | The two stars should be the same age, so we'd expect the subgiant to be more massive than the main-sequence star. |
| How will an isolated, one solar-mass star die? | As a white dwarf |
| If someone somehow added a lot more hydrogen and helium to the Sun (say 50% more than it has now), what would happen to it? | It would begin to evolve much more quickly than it is now. |
| The luminosity of light emerging from the star's gaseous surface is equal to the . . . | rate of energy generated from nuclear reactions in the star's core. |
| Main Sequence | An area on the Hertzsprung-Russel diagram that runs from lower left to lower right and includes more then 90% of all stars. |
| Main-sequence phase | surface radiates energy at same rate that core generates energy lasts about 10 billion years energy generated by nuclear fusion |
| How much more abundant is hydrogen in the universe than nitrogen? | Hydrogen is 10,000 times more abundant than nitrogen. Notice that the dot for nitrogen is at 10-4 = 1/10,000 on the vertical (abundance) axis |
| The famous Crab Nebula. What is it? | An expanding cloud of remains from a star that died in a supernova. Humans on Earth witnessed the explosion in 1054 A.D. |
| a supernova in the photo on the right. What can we conclude about this star? | It was a high-mass star with at least 8 times the mass of the Sun. Only high-mass stars explode as supernovae. |
| the 1987 explosion of a giant bluish star in the Milky Way galaxy’s largest satellite galaxy, the Large Magellanic Cloud, a luminous blob that is easily visible south of the equator. | looked like a single star in the night sky. The size of the blob in the photo is an artifact of the photography; the star is so far away that even as it explodes it would appear as a point of light not even as bright as some nearby stars in night sky. |
| A typical white dwarf is _________. | As massive as the sun but only as large as in size as the Earth. |
| Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit? | The white dwarf will explode completely as a white dwarf supernova. |
| Pulsars are thought to be _________. | Rapidly rotating neutron stars. |
| Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass (1 solar mass). What would happen to Earth in its orbit? | Nothing—Earth's orbit would remain the same. |
| The white dwarf that remains when our Sun dies will be mostly made of ________. | Carbon |
| Will our Sun ever undergo a white dwarf supernova explosion? Why or why not? | No because it is not orbited by another star. |
| What do we mean by the event horizon of a black hole? | It is the point beyond which neither light nor anything else can escape the black hole's gravity. |
| The Schwarzschild radius of a black hole depends on ________. | is proportional to the mass, Sr=2Gm/c2 |
| White Dwarf Supernova Traits. | Star explodes completely,leaving no compact object bejind. Can only occur in a binary system. Can occur in a very old star cluster. Has a brighter peak luminosity. Spectra always lack strong hydrogen lines. |
| Massive star Supernova | Black hole or neutron star left behind. Can only occur in a galaxy with ongoing star formation. |
| In general, we can detect a black hole left behind by a dead star __________. | only if mass is being transferred to it by another star. In other words, we an generally detect black holes (of stellar mass) only in binary systems with mass transfer. |
| The radius of a white dwarf is determined by a balance between the inward force of gravity and the outward push of _______. | Electron Degeneracy pressure |
| A(n) ________ occurs when hydrogen fusion ignites on the surface of a white dward in a binary system | Nova |
| A(n) _______ occurs when fusion creates iron in the core of a star. | Massive star Supernova |
| A white dwarf in a close binary system will explode as a supernova if it gains enough mass to exceed the _________. | White dwarf limit (1.4 solar masses) |
| A(n) ________ consists of hot, swirling gas captured by a white dwarf (or neutron star or black hole) from a binary companion star. | accretion disk |
| A(n) __________ can occur only in a binary system, and all such events are thought to have the same luminosity | white dwarf supernova. |
| Which has the smallest radius: A 1.2Msun white dwarf, a 0.6Msun white dwarf, or jupiter? | Jupiter is far larger than the other two. White dwarfs can be treated as Fermi gasses, and have the interesting property that as their mass increases their radius decreases. So the smallest is actually the 1.2 solar mass white dwarf. |
| A typical neutron star is more massive than our Sun and about the size (radius) of _________. | a small asteroid (10 km in diameter) |
| What makes us think that the star system Cygnus X-1 contains a black hole? | It emits X rays characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star. |
| The following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit? | Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit. |
| According to our modern understanding, what is a nova? | an explosion on the surface of a white dwarf in a close binary system |
| Which of the following statements about electron degeneracy pressure and neutron degeneracy pressure is true? | Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy pressure is the main source of pressure in neutron stars. |
| How would a flashing red light appear as it fell into a black hole? | Its flashes would shift to the infrared part of the spectrum. Gradually becoming "redder" |
| White dwarf characteristics (a) | May be surrounded by a planetary nebula. Emits strongly in visible and ultraviolet, and may be in a binary system that undergoes nova explosions. |
| Neutron star (characteristics) | May be in a binary system that undergoes x-ray bursts. Can have a mass of 1.5 solar masses, may be surrounded by a supernova remnant, may be repeatedly dim and brighten more than once per second. |
| Black Hole only can have | a mass of infinite solar mass, it is also detectable only if it is accreting gas from other objects. |
| An X-ray binary is a binary star system in which gas from an ordinary star is accreting onto a compact object. The accreting gas emits X rays because it __________. | is very hot. The gas becomes hot because it converts a lot of gravitational potential energy into heat as it falls toward an extremely compact object, such as a neutron star or a black hole. |
| Description of a white dwarf | A white dwarf is the hot, compact corpse of a low-mass star, typically with a mass similar to the Sun compressed to a volume the size of the Earth. |
| Description of a neutron star | A neutron star is the 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. |
| Description of a black hole | an object in which gravity has overcome all sources of pressure support, causing collapse without end. Its event horizon is the place from within which no information can leave the BH. Schwarzschild radius of BH defines the “size” of the event horizon. |
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tshawboy
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