Download Test #4 (Ch. 13-16) ASTR 10 You have 1 hour to take the exam, and

Test #4 (Ch. 13-16)
ASTR 10
You have 1 hour to take the exam, and you can keep your copy of the test once you’re done. A list of answers to this exam will post
to the course website next week, so you can have feedback on the exam before the final.
1. Which two processes can generate energy to help a star maintain its internal thermal pressure?
A. nuclear fusion and supernova
B. nuclear fission and supernova
C. nuclear fusion and gravitational contraction
D. nuclear fusion and nuclear fission
2. Our Sun is considered to be a(n) ________.
A. intermediate-mass star
B. high-mass star
C. low-mass star
D. brown dwarf
3. Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse?
A. The cloud must collide with other clouds.
B. New dust particles must continually be made in the cloud.
C. The cloud must radiate much of its thermal energy.
D. The cloud must trap most of its thermal energy.
4. Consider a large molecular cloud that will give birth to a cluster of stars. Which of the following would you expect to be true?
A. All the stars in the cluster will become main-sequence stars at about the same time.
B. All the stars in the cluster will be of about the same mass.
C. A few massive stars will form, live, and die before the majority of the star's clusters even complete their protostar stage.
D. All the stars in the cluster will have approximately the same luminosity and surface temperature.
5. We do not know for certain whether the general trends we observe in stellar birth masses also apply to brown dwarfs. But if they do,
then which of the following would be true?
A. Brown dwarfs would be responsible for most of the overall luminosity of our Milky Way Galaxy.
B. Most of the brown dwarfs in the Milky Way Galaxy would be quite young in age.
C. Brown dwarfs would outnumber all ordinary stars.
D. Brown dwarfs would be extremely rare.
6. Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars?
A. H-R diagrams of open clusters
B. spacecraft observations of the Sun
C. H-R diagrams of globular clusters
D. observing a low-mass star over many years
7. Carbon fusion occur in high-mass stars but not in low-mass stars because ________.
A. only high-mass stars do fusion by the CNO cycle
B. the cores of low-mass stars never get hot enough for carbon fusion
C. the cores of low-mass stars never contain significant amounts of carbon
D. carbon fusion can occur only in the stars known as carbon stars
8. Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, and so on) in a highmass star is not true?
A. Each successive stage lasts for approximately the same amount of time.
B. As each stage ends, the reactions that occurred in previous stages continue in shells around the core.
C. As each stage ends, the core shrinks and heats further.
D. Each successive stage creates an element with a higher atomic number and atomic mass number.
9. This diagram represents the life track of a 1 solar mass star. Refer to the life stages labeled with roman numerals. During which
stage does the star have an inert (non-burning) helium core?
A. II
B.III
C.IV
D.V
E. VI
10. The ultimate fate of our Sun is to ________.
A. become a rapidly spinning neutron star
B. become a black hole
C. become a white dwarf that will slowly cool with time
D. explode in a supernova
11. Why is iron significant to understanding how a supernova occurs?
A. Iron is the heaviest of all atomic nuclei, and thus no heavier elements can be made.
B. Iron cannot release energy either by fission or fusion.
C. Supernovae often leave behind neutron stars, which are made mostly of iron.
D. The fusion of iron into uranium is the reaction that drives a supernova explosion.
12. After a supernova explosion, the remains of the stellar core ________.
A. will always be a neutron star
B. may be either a neutron star or a black hole
C. will always be a black hole
D. may be either a white dwarf, neutron star, or black hole
13. Algol consists of a 3.7 MSun main-sequence star and a 0.8 MSun subgiant. Why does this seem surprising, at least at first?
A. It doesn't make sense to find a subgiant in a binary star system.
B. The two stars in a binary system should both be at the same stage of life; that is, they should either both be main sequence stars or
both be subgiants.
C. A star with a mass of 3.7 MSun is too big to be a main sequence star.
D. The two stars should be the same age, so we'd expect the subgiant to be more massive than the main-sequence star.
14. The more massive a white dwarf, the ________.
A. larger its radius
B. smaller its radius
C. higher its luminosity
D. higher its temperature
15. The white dwarf that remains when our Sun dies will be mostly made of ________.
A. neutrons
B. carbon
C. helium
D. hydrogen
16. According to present understanding, a nova is caused by ________.
A. a white dwarf that gains enough mass to exceed the 1.4-solar-mass limit
B. hydrogen fusion on the surface of a neutron star
C. carbon fusion in the core of a white dwarf
D. hydrogen fusion on the surface of a white dwarf
17. Which statement about pulsars is not thought to be true?
A. Pulsars can form only in close binary systems.
B. A pulsar must have a very strong magnetic field and rotate quite rapidly.
C. All pulsars are neutron stars, but not all neutron stars are pulsars.
D. Pulsars are kept from collapsing by neutron degeneracy pressure.
18. Suppose that a white dwarf primarily made of carbon is gaining mass through accretion in a binary system. What happens if the
mass someday reaches the 1.4 solar mass limit?
A. The white dwarf will undergo a nova explosion.
B. The white dwarf will collapse in size, becoming a neutron star.
C. The white dwarf will collapse to become a black hole.
D. The white dwarf will explode completely as a white dwarf supernova.
19. Degeneracy pressure stops the crush of gravity in all the following except
A. a brown dwarf.
B. the central core of the Sun after hydrogen fusion ceases but before helium fusion begins.
C. a neutron star.
D. a very massive main-sequence star.
E. a white dwarf.
20. There is no upper limit to the mass of a neutron star.
A. True
B. False
21. How does the interstellar medium affect our view of most of the galaxy?
A. It prevents us from seeing most of the galactic disk with visible and ultraviolet light.
B. It has no effect on visible-light observations, but prevents us from studying the galactic center with radio waves or X-rays.
C. It absorbs all wavelengths of light.
D. It produces so much visible light that it blocks our view of anything beyond it.
22. How would you expect a star that formed recently in the disk of the galaxy to differ from one that formed early in the history of
the disk?
A. It should orbit the galactic center at a much higher rate of speed.
B. It should be higher in mass.
C. It should be much brighter.
D. It should have a higher fraction of elements heavier than hydrogen and helium.
E. All of the above would be expected.
23. If you could watch a time-lapse movie of the interstellar medium over hundreds of millions of years, what would you see?
A. The movie would alternate back and forth between being very bright when there is a lot of gas and very dark when there is very
little gas.
B. Gas that is often moving at high speed, particularly after one or more supernovae, and constantly changing form between molecular
clouds, atomic hydrogen, and hot, ionized bubbles and superbubbles
C. The entire disk of the Milky Way would pulsate in and out as it contracts to form stars and then blows out in supernovae and then
contracts to form stars again and so on.
D. Gas that changes only in very slow and steady ways, so that the movie would in fact be quite boring
24. Red and orange stars are found evenly spread throughout the galactic disk, but blue stars are typically found ________.
A. only in or near star-forming clouds
B. in the halo
C. also evenly spread throughout the galactic disk
D. only in the central bulge
25. What evidence suggests that most of the mass of the Milky Way is in the form of dark matter?
A. Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see
in the Milky Way disk.
B. Although dark matter emits no visible light, we have detected its radio emissions.
C. The orbital speeds of stars far from the galactic center are surprisingly high.
D. Our view of distant galaxies is often obscured by dark blotches, which are presumably made of dark matter.
26. If we could watch spiral arms from a telescope situated above the Milky Way over 500 million years, what would we see happen?
A. Stars will move through the spiral arms, bunching up closer as they pass through. Young hot stars will form and die within the arms
before having a chance to move out.
B. The spiral arms will eventually dissipate and fade away, since they are a temporary phenomenon that should only last for a million
years or so.
C. The spiral arms will eventually unwind, as centripetal forces send the stars flying outwards into intergalactic space.
D. The spiral arms will seem to "wind up," to wrap more and more tightly around the center of the Galaxy.
27. How does the diameter of the disk of Milky Way Galaxy compare to its thickness?
A. The diameter and thickness are roughly equal.
B. The diameter is about 100 times as great as the thickness.
C. The diameter is about 10 times as great as the thickness.
D. The diameter is about 100,000 times as great as the thickness.
28. What do we call the bright, sphere-shaped region of stars that occupies the central few thousand light-years of the Milky Way
Galaxy?
A. a globular cluster
B. the galaxy's disk
C. the galaxy's halo
D. the galaxy's bulge
29. What are the Magellanic Clouds?
A. two nebulae located in the disk of the Milky Way galaxy and visible only from the Southern Hemisphere
B. two small galaxies that orbit the Milky Way Galaxy
C. the clouds of dust and gas found interspersed in many places throughout the Milky Way Galaxy
D. star-forming clouds found in the constellation Orion
30. What do we mean by a protogalactic cloud?
A. a cloud of hydrogen and helium that contracts to become a galaxy
B. the cloud-like halo that surrounds the disks of spiral galaxies
C. a term once used historically to refer to any galaxy
D. a cloud of gas that was once a galaxy
31. The most basic difference between elliptical galaxies and spiral galaxies is that ________.
A. elliptical galaxies lack anything resembling the halo of a spiral galaxy
B. elliptical galaxies lack anything resembling the disk of a spiral galaxy
C. elliptical galaxies are very old and spiral galaxies are very young
D. elliptical galaxies have a spheroidal component (of stars distributed spherically about the galactic center), and spiral galaxies do not
32. Using the technique of main-sequence fitting to determine the distance to a star cluster requires that ________.
A. we use ultraviolet and X-ray telescopes
B. we have telescopes powerful enough to allow us to identify the spectral types of many main-sequence stars in the cluster
C. the cluster be near enough for us to measure the parallax of its stars
D. we have a well-calibrated period-luminosity relation for Cepheid variable stars
33. Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10
days. What can we learn from this observation?
A. We can learn the distance to the galaxy.
B. Under the rules of the International Astronomical Union, we will be entitled to naming rights for the galaxy.
C. It will allow us to calculate the rotation rate of the galaxy.
D. It will allow us to determine the mass of the galaxy.
34. Why are white dwarf supernovae more useful than massive star supernovae for measuring cosmic distances?
A. White dwarf supernovae are much more common than massive star supernovae.
B. White dwarf supernovae follow a period-luminosity relation, while massive supernovae do not
C. We can see only white dwarf supernovae in distant galaxies, not massive star supernovae.
D. White dwarf supernovae all have roughly the same true peak luminosity, while massive supernovae come in a wide range of peak
luminosities.
35. Does Hubble's law work well for galaxies in the Local Group? Why or why not?
A. No, because Hubble did not know the Local Group existed when he discovered his law.
B. No, because we do not know the precise value of Hubble's constant.
C. No, because galaxies in the Local Group are gravitationally bound together.
D. Yes, it works so well that we have never detected any measurable deviations from its predictions.
36. What does cosmological redshift do to light?
A. makes it slow down
B. makes all light infrared
C. makes it brighter
D. stretches its wavelength
37. Although the entire universe may be much larger than our observable universe, we can see only within our observable universe.
The "boundary" of our observable universe is called ________.
A. the Big Bang
B. the Hubble Deep Field
C. the cosmological horizon
D. the lookback time
38. Which of the following is an important starting assumption in models of galaxy formation?
A. Black holes form first, seeding the formation of galaxies.
B. All galaxies start out as spiral galaxies.
C. Some regions in the universe start out denser than others.
D. Galaxies form first, then black holes.
39. Which of the following types of galaxies have a disk and spheroidal component but lack spiral arms?
A. irregulars
B. ellipticals
C. lenticulars
D. all of the above
40. A protogalactic cloud with slow star formation is more likely to form a spiral galaxy than an elliptical galaxy.
A. True
B. False