Astro Exam 4

1. What do we see when we look beyond the cosmological horizon? a. Galaxies that are just about to form. b. White dwarfs that are about to go supernova. c. Galaxies that are about to enter the universe. d. The beginning of the universe. e. We cannot look beyond the cosmological horizon because we cannot look back to a time before the universe began.

2. What does the universe look like on very large scales? a. Galaxies appear to be distributed in chains and sheets that surround great voids. b. Galaxies are uniformly distributed. c. Galaxies are distributed in a hierarchy of clusters, superclusters, and hyperclusters. d. Galaxies are distributed in a great shell expanding outward from the center of the universe. e. Galaxies are randomly distributed.

3. What fraction of the mass of spiral galaxies is in dark matter? a. About 60% b. About 10% c. About 1% d. About 30% e. About 90%

4. Homogeneity means that there is no preferred location in the Universe. That is, no matter where you are in the Universe, if you look at the Universe, it will look the same. a. True b. False

5. True or False? So far, clusters of galaxies are the largest structures that have been detected in the universe. a. False, there are several nearby galaxies that have a much larger angular size than distant galaxy clusters. b. False, quasars are the largest objects in the universe. c. True, the largest clusters stretch halfway across the sky. d. True, some clusters have been found to contain thousands of galaxies. e. False, clusters are themselves part of even larger superclusters.

6. When we speak of the large-scale structure of the universe, we mean a. The overall arrangement of galaxies, clusters of galaxies, and superclusters in the universe. b. The overall shape of the observable universe. c. The structure of any individual cluster of galaxies. d. The structure of any large galaxy.

7. How did dark matter contribute to the formation of galaxies? a. The gravitational pull of dark matter led to the formation of protogalactic clouds. b. Dark matter helped radiate energy allowing protogalactic clouds to collapse. c. The gravitational pull of dark matter triggered the collapse of the first star-forming regions. d. The gravitational pull of dark matter prevented young galaxies from blowing apart from super bubbles created by the first generation of supernovae.

8. Suppose that the universe has more dark matter than we think there is today. How would this change the age we estimate from the expansion rate? a. Our Universe would not exist with more dark matter, so we cannot answer the question. b. The estimated age would be smaller. c. The estimated age would be the same. d. The estimated age would be larger.

9. If the density of the universe is less than the critical density and there is dark energy, what is the expansion pattern of the universe? a. A recollapsing universe e. a repeating universe b. An accelerating universe c. A coasting universe d. A critical universe

10. Which astronomical object lives the longest? a. Black Holes b. Stellar remnants c. Stars

11. In what order will these things "disappear" by the year 10100? a. Baryons, stars, black holes b. Black holes, baryons, stars c. Stars, baryons, black holes d. Stars, black holes, baryons

12. What would happen if the Universe settled into a new vacuum? a. The Universe changes to the new state instantaneously. b. Nothing c. Bubbles of the new vacuum state grow at the speed of light and reset the fabric of spacetime to the new state, but matter and energy is unchanged. d. Bubbles of the new vacuum state grow at the speed of light and destroy everything in the Universe

13. What is entropy? a. A measure of disorder in a system b. A measure of order in a system c. A measure of structure in the Universe d. A measure of redshift of a galaxy

14. What is the Cosmological Principle? a. Matter is evenly distributed throughout the universe. b. Hubble's constant has the same value at all locations in the universe. c. The rate of expansion of spacetime has been uniform since the Big Bang. d. The laws of physics are the same everywhere in the universe.

15. As a photon traveling through intergalactic space, its wavelength is stretched as the space through which it is traveling expands. This is called a cosmological redshift. a. True b. False

16. What might be causing the universe to accelerate? a. We don't know!-but we call it "dark energy." b. White-dwarf supernovae c. Dark gravity d. Neutrinos e. WIMPs

17. What is the evidence for an accelerating universe? a. There is far more dark matter than visible matter in the universe. b. White-dwarf supernovae are slightly brighter than expected. c. The Andromeda Galaxy is moving away from the Milky Way at an ever-increasing speed. d. White-dwarf supernovae are slightly dimmer than expected. e. White-dwarf supernovae are the same brightness regardless of redshift.

18. Some galaxy clusters are still growing today. a. True b. False

19. What needs to be true for the universe to expand more and more slowly and end up in a "Big Chill" (critical universe)? a. Matter density equals the critical density b. Matter density is less than the critical density c. Requires dark energy to drive the expansion d. Matter density is greater than the critical density

20. What observations provide evidence for dark energy? a. Spatial distribution and redshifts of quasars b. Distances and redshifts of white dwarf supernovae c. Velocity dispersion of galaxy clusters d. Distances and redshifts of quasars

21. Which of the following is not a technique used to measure the total mass of a cluster of galaxies? a. Observations of the temperature of the hot intracluster medium b. Observations of the motions of galaxies within the cluster c. Observations of the luminosity of the galaxies d. Observations of gravitational lensing of galaxies behind the cluster

22. The critical density of the universe is the ______. a. Density of water b. Actual average density of the universe c. Density of dark matter in the universe d. Average density the universe would need for gravity to someday halt the current expansion if dark energy did not exist

23. How much more mass is in the hot gas of the intracluster medium than in stars in clusters of galaxies? a. There are about equal amounts of hot gas and stars in galaxy clusters b. About 300 times as much hot gas c. About 7 times as much hot gas d. About 50 times as much hot gas

24. Including dark matter, what is the apparent density of the universe compared to the critical density? a. One one-thousandth (0.1%) of the critical density b. Approximately equal to the critical density c. One two-hundredth (0.5%) of the critical density d. One-fourth of the critical density e. One-tenth of the critical density

25. Which statement below correctly describes the relationship between expansion rate and age for the universe? a. The faster the rate of expansion, the older the age of the universe b. The faster the rate of expansion, the younger the age of the universe c. Age is independent of the expansion rate

26. Which region of the early universe was most likely to become a galaxy? a. A region with an unusual concentration of dark energy b. A region whose matter density was higher than average c. A region whose matter density was lower than average

27. What did astronomers expect might cause the expansion of the universe to slow down? a. The gravitational pull of all the matter in it b. Being very old c. Friction d. Running out of energy e. None of the above

28. When we use an analogy that represents the expanding universe with the surface of an expanding balloon, what does the inside of the balloon represent? a. It represents the center of the universe b. It represents regions of the universe beyond the Milky Way Galaxy c. It represents the entire universe d. The inside of the balloon does not represent any part of our universe

29. Which of the following best describes the status of the Milky Way in our Local Group of galaxies? a. It is by far the largest galaxy in the group b. It is one of the two largest galaxies in the group c. It is quite average among the galaxies in the group d. It is one of about a dozen large spiral galaxies in the group

30. Which of the following statements best summarizes current evidence concerning dark matter in individual galaxies and in clusters of galaxies? a. Within individual galaxies, dark matter is always concentrated near the galactic center, and within clusters it is always concentrated near the cluster center b. Dark matter is present between galaxies in clusters, but not within individual galaxies c. Dark matter is present in individual galaxies, but there is no evidence that it can exist between the galaxies in a cluster d. Dark matter is the dominant form of mass in both clusters and in individual galaxies

31. Why does the temperature of the gas between galaxies in galaxy clusters tell us about the mass of the cluster? a. The temperature of the gas tells us the gas density, so we can use the density to determine the cluster's mass b. The temperature is always directly related to mass, which is why massive objects are always hotter than less massive objects c. The temperature tells us the average speeds of the gas particles, which are held in the cluster by gravity, so we can use these speeds to determine the cluster mass d. The question is nonsense - cannot be done

32. What cosmic property makes the idea of everything you see in the universe as the consequence of a "Boltzmann brain" possibly appealing a. B and C b. Black holes c. None of the above d. Dark energy e. All of the above f. Dark matter

33. As the universe expands, so do the objects within the universe. Hence, our galaxy and all galaxies within a cluster are now more spread out than they were billions of years ago. a. True b. False

34. What does it mean to say that our universe is expanding? a. Space itself is expanding b. Everything is expanding, including galaxies, star clusters and star systems c. Galaxies are moving apart through space

35. The flat rotation curves of spiral galaxies tell us that they contain a lot of dark matter. Do they tell us anything about where the dark matter is located within the galaxy? a. Yes, they tell us that dark matter is spread throughout the galaxy, with most located at large distances from the galactic center b. No, we cannot determine anything about the location of dark matter from the rotation curve c. Yes, they tell us that dark matter is spread uniformly throughout the galactic disk d. Yes, they tell us that dark matter is concentrated near the center of the galaxy

36. According to you reading, what is a "type III multiverse" a. Universes that are disconnected by distance (different horizons) b. Universes that are separated by higher dimensions c. Universes that have distinct laws of physics d. Universes that are different realizations of outcomes of events e. Universes that are distinct in time

37. What is a key problem in the original Boltzmann brain idea when it was originally postulated? a. B and C b. All of the above c. Astronomers thought the universe had been around forever d. Astronomers did not know about dark energy e. Astronomers did not know about dark matter

38. Which of the following possible types of universe would not expand forever? a. An accelerating universe b. A critical universe c. A recollapsing universe

39. True or False? If you want to find elliptical galaxies, you'll have better luck looking in clusters of galaxies than elsewhere in the universe a. False, elliptical galaxies are never found in galaxy clusters b. True, galaxy cluster have a much higher percentage of elliptical galaxies than do other parts of the universe c. True, elliptical galaxies are found exclusively in galaxy clusters d. False, you would have an equal chance of finding an elliptical galaxy in any environment in the universe e. False, elliptical galaxies are more commonly found away from galaxy clusters

40. What happens to the entropy of the Universe with time? a. It increases b. It decreases c. It stays constant

41. What does Hubble's law tell us? a. The longer the period of a Cepheid variable, the greater its luminosity b. For every force, there is an equal and opposite reaction force c. The more distant a galaxy, the faster it is moving away from us d. The faster a spiral galaxy's rotation speed, the more luminous it is

42. Which of the following statements about rich clusters of galaxies (those with thousands of galaxies) is FALSE? a. Galaxies in the central regions are predominantly spirals, which elliptical galaxies roam the outskirts b. There likely have been numerous collisions among the member galaxies at some time in the past c. They are sources of X-ray emission due to the presence of hot, intergalactic gas d. They often have a very large, central dominant galaxy near their center, perhaps formed by the merger of several individual galaxies e. The speeds of the galaxies in the cluster indicate that most of the cluster mass is dark matter

43. True or False? A cluster of galaxies is held together by the mutual gravitational attraction of all the stars in the cluster's galaxies. a. False, the amount of mass in cluster's stars is much lower than the amount needed to hold the cluster together b. False, the focusing effect of gravitational lensing prevents individual galaxies from leaving a cluster c. True, a large cluster can contain many billions of stars, sufficient to hold the cluster together d. True, in the same way that the mutual gravitational attraction of all the stars in the Milky Way holds it together e. False, X-ray observations show that the hot gas between the clusters has enough mass to hold clusters together

44. What is the Sloan Great Wall a. A huge spherical bubble formed by galaxies, surrounding a void b. The dense distribution of primitive galaxies at the boundary of the observable universe c. A huge sheet of galaxies more than 1 billion light-years long d. A vast cloud of intergalactic gas that blocks our view of certain distant regions of the universe

45. Which one of these is FALSE? What does the accelerating expansion of the universe imply for the fate of the universe? a. Black holes will continue to grow by accreting any matter that comes too close b. After 100 trillion years (1012), there won't be enough remaining gas for making new stars, and the last stars will have died c. Many new stars will be made by the collision and merger of brown dwarfs d. The Milky Way will disintegrate as it stars will interact with each other and will be kicked into intergalactic space e. The remaining matter will consist of brown dwarfs, white dwarfs, black holes, and a little gas and dust

46. The expansion rate of the universe appears to be the same everywhere in space. a. True b. False

47. What are the largest structures in the universe? a. Uniform arrangements of galaxies over the largest distances b. Voids, walls, sheets, and chains of galaxies c. Galaxies d. Superclusters of galaxies e. Clusters of galaxies f. Superclusters of galaxies

48. Two universes in a multiverse can be separated by the following, except: a. Probability (if multiverses extend to all possible outcomes of all events) b. Distance (two observers can be outside each other's observable horizon or are in vastly distant regions separated by inflation) c. Physical laws (two observers live in universes with different physical constants or mathematical laws) d. Time (two observers are separated by time) e. Dimension (two observers are separated by higher spatial dimension than we can perceive)

49. The structures seen in the universe today a. Were produced by supernovae b. Are probably relatively new c. Probably come from the distribution of dark matter when the universe was young d. Correspond to computer simulations of structure formation e. C and D

50. Gravitational lensing occurs when a. Dark matter builds up in a particular region of space, leading to a very dense region and an extremely high mass-to-light ratio b. Telescope lenses are distorted by gravity c. Massive objects cause more distant objects to appear much larger than they should and we can observe the distant object with better resolution d. Massive objects bend light beams that are passing nearby