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Unformatted text preview: 1 Chapter 22 Post‐Chapter Quiz 1. What is the rotation curve of a spiral galaxy? 1. The curvature of its arms 2. How fast it rotates 3. A plot of rotation speed vs. distance from the center 4. The maximum speed a galaxy can rotate 2. Why are the absorption lines of elliptical galaxies wide? 1. The galaxies are moving away from us 2. The galaxies are rotating 3. Some stars in them are going away from us, some toward us, so we get red and blueshifts –which make lines wider 4. The stars in elliptical galaxies have wider lines than the stars in spirals 3. What do the (fast) speeds of stars in elliptical galaxies tell us? 1. These galaxies may be breaking up 2. There must be a lot of dark matter whose gravity can be felt but which isn’t seen 3. These galaxies must have had collisions 4. None of the above 4. How are rotation curves of spiral galaxies determined beyond radii where starlight can be detected? 1. by extrapolation 2. through observations of spectral lines of dark matter 3. by measuring the broadening of absorption lines 4. by watching the galaxies rotate over a period of years 5. through observations of the 21 cm line of atomic hydrogen 5. What is the effect of dark matter on the formation of the structure of galaxies and clusters of galaxies? 1. None–the matter is dark 2. Existant, but so small it can be discounted 3. Gravity of dark matter is what caused protogalactic clouds to contract early in time 4. We don’t know, because we don’t know the distribution of dark matter 5. Probably none. Since the matter is dark we can’t be sure it is there 6. What did astronomers expect might cause the expansion of the universe to slow down? 1. Friction 2. Running out of energy 3. Being very old 4. The gravitational pull of all the matter in it 5. None of the above 2 7. What is actually happening to the expansion of the universe? 1. It is continuing more or less unchanged 2. It is slowing down 3. It is accelerating 4. None of the above 8. Astronomers now believe that most of any galaxy’s mass lies beyond the portions of the galaxy that we can see. 1. Yes, because the orbital velocity of gas and stars remains fairly constant as we look farther from the galactic center, even beyond where most stars are found. 2. Yes, because dark matter telescopes show massive halos well beyond where stars are found. 3. Yes, because the mass‐to‐light ratio of galaxies is much less than the value for the Sun. 4. Yes, because the mass‐to‐light ratio of galaxies is much greater than the value for the Sun. 5. No, once we take into consideration the gas in a galaxy as well as the stars, we can account for all its mass. 9. A cluster of galaxies is held together by the mutual gravitational attraction of all the stars in the cluster’s galaxies. 1. Yes, in the same way that the mutual gravitational attraction of all the stars in the Milky Way holds it together. 2. Yes, a large cluster can contain many billions of stars, sufficient to hold the cluster together. 3. No, the amount of mass in a cluster’s stars is much lower than the amount needed to hold the cluster together. 4. No, X‐ray observations show that the hot gas between the clusters has enough mass to hold clusters together. 5. No, the focusing effect of gravitational lensing prevents individual galaxies from leaving a cluster. 10. Gravitational lensing occurs when 1. dark matter builds up in a particular region of space, leading to a very dense region and an extremely high mass‐to‐light ratio. 2. telescope lenses are distorted by gravity. 3. massive objects bend light beams that are passing nearby. 11. What do we mean when we say that a particle is a weakly interacting particle? 1. It is the only type of particle that interacts through the weak force. 2. It interacts only through the weak force. 3. It interacts only through the weak force and the force of gravity. 4. It is so small that it doesn't affect objects in the universe. 5. It doesn't interact with any type of baryonic matter. 3 12. The distribution of the dark matter in a spiral galaxy is 1. predominantly concentrated in the spiral arms. 2. approximately spherical and about the same size as the galaxy halo. 3. flattened in a disk and about the same size as the stellar disk. 4. flattened in a disk but about ten times larger than the stellar disk. 5. approximately spherical and about ten times the size of the galaxy halo. 13. What is meant by "dark energy"? 1. the total energy in the Universe after the Big Bang but before the first stars 2. highly energetic particles that are believed to constitute dark matter 3. the agent causing the universal expansion to accelerate 4. the energy associated with dark matter through E=mc2 14. Which model of the universe gives the youngest age for its present size? 1. all models give the same age 2. a recollapsing universe 3. a coasting universe 4. an accelerating universe 15. What is the evidence for an accelerating universe? 1. The Andromeda Galaxy is moving away from the Milky Way at an ever‐increasing speed. 2. White‐dwarf supernovae are the same brightness regardless of redshift. 3. There is far more dark matter than visible matter in the universe. 4. White‐dwarf supernovae are slightly brighter than expected for a coasting universe. 5. White‐dwarf supernovae are slightly dimmer than expected for a coasting universe. 16. Why do we expect WIMPs to be distributed throughout galactic halos, rather than settled into a disk? 1. Shock waves from supernovae have blown the WIMPs out into the halo. 2. WIMPs were produced at the early stages of galaxy evolution, and objects in the halo, such as globular clusters, were formed at the beginning of the galaxy. 3. They are light enough that they have expanded out into the halo. 4. Since they do not interact with the electromagnetic force, they do not feel friction or drag so they cannot radiate away their orbital energy and hence do not contract with the rest of the protogalactic cloud. 5. Jets from the early active stage of a galaxy's life shot out most of the WIMPs from the disk. 17. Some MACHOs emit radiation. Why are they considered dark matter? 1. They emit radiation only in the form of particles of dark matter. 2. They are not as bright as a normal star and are not visible across great distances of space. 3. They are made of particles of dark matter that release some radiation. 4 18. Why isn't space expanding within systems such as our solar system or the Milky Way? 1. We are so close to these systems that we don't observe their expansion. 2. The universe is not old enough yet for these objects to begin their expansion. 3. Hubble's law of expansion applies only to the space between galaxies. 4. Their gravity is strong enough to hold them together against the expansion of the universe. 19. Why do we think there is much dark matter in clusters of galaxies? 1. Individual galaxies are moving so fast that they could not be held together by the gravity of visible matter 2. We’ve detected some of it with dark telescopes 3. The X rays seen coming from cluster of galaxies arise in very hot clouds of gas that could only be held in the cluster by very strong gravity 4. Bending of starlight (gravitational lensing) lets us measure mass even when we can’t see it 5. All except 2 20. What percentage of the universe is made up of normal matter, dark matter, and dark energy? 1. 33% normal matter, 33% dark matter, 33% dark energy 2. 4% normal matter, 25% dark matter, 71% dark energy 3. 4% normal matter, 71% dark matter, 25% dark energy 4. 25% normal matter, 71% dark matter, 4% dark energy ...
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This note was uploaded on 03/03/2011 for the course RSM 100 taught by Professor Oesch during the Spring '08 term at University of Toronto- Toronto.
- Spring '08