21st century astronomy the solar system fifth edition test bank chapter 23 by asmacandy

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Chapter 23: Large-Scale Structure in the Universe LEARNING OBJECTIVES Define the boldfaced vocabulary terms within the chapter. 23.1 Galaxies Form Groups, Clusters, and Larger Structures Compare and contrast groups, clusters, superclusters, and walls. Multiple Choice: 1, 2, 3, 4, 6, 7, 9, 10, 13, 18 Short Answer: 1, 8 Summarize the evidence for dark matter dominating the mass of groups and clusters. Multiple Choice: 12, 14, 15, 16, 17 Short Answer: 2, 3, 4, 5, 7 Describe how Hubbleâ&#x20AC;&#x2122;s law helps astronomers map the structure of mass in the universe. Multiple Choice: 5, 8, 11 Short Answer: 6 23.2 Gravity Forms Large-Scale Structure Illustrate the steps that led to large-scale structure formation.

Multiple Choice: 20, 21, 26, 37, 38 Describe how gravitational instabilities created the seeds of large-scale structure. Multiple Choice: 19, 22, 23, 29, 36 Short Answer: 11 Relate the presence of dark matter to the formation of galaxies in the early universe. Multiple Choice: 24, 25, 34, 39 Short Answer: 14 Summarize the observational evidence that dark matter cannot be composed of ordinary matter. Multiple Choice: 27, 30, 33, 35 Compare and contrast the properties and possible constituents of cold and hot dark matter. Multiple Choice: 28, 31, 32 Short Answer: 9, 15, 16 Describe the collapse of cold dark matter into a galaxy halo after recombination. Short Answer: 10 23.3 First Light of Stars and Galaxies Describe the properties of the very first generation of stars and whether these are based on observations or hypotheses. Multiple Choice: 44, 47, 48, 52 Short Answer: 24 Explain why the first generation of stars were expected to be very massive, while subsequent generations could have high and low mass. Multiple Choice: 45, 53, 54 Short Answer: 25, 28 Describe the properties of the first generation of galaxies and whether these are based on observations or hypotheses. Multiple Choice: 46, 49, 55 Short Answer: 12, 13, 27 Compare and contrast the processes of star and galaxy formation. Multiple Choice: 50, 51 Short Answer: 23, 26 23.4 Galaxies Evolve

Describe the hierarchical formation scenario that built up fragments into todayâ&#x20AC;&#x2122;s galaxies. Short Answer: 29 Summarize the observational evidence that galaxies formed by hierarchical merging. Multiple Choice: 57, 65, 67, 68 Short Answer: 32 Relate the formation of supermassive black holes to galaxy evolution and star-formation rates. Multiple Choice: 58, 66, 69, 71, 73 Compare and contrast the results of cosmological simulations to measurements of cosmic structure. Multiple Choice: 59, 60, 63, 64, 70 Short Answer: 30, 31 Describe the expected stages of future evolution of our universe. Multiple Choice: 56, 61, 62, 72 Working It Out 23.1 Use orbital properties of galaxies to calculate their mass. Working It Out 23.2 Calculate the observed wavelength of highly redshifted light. Multiple Choice: 40, 41, 42, 43 Short Answer: 17, 18, 19, 20, 21, 22

MULTIPLE CHOICE 1. Which of these shows the correct order of collections of galaxies, starting with the smallest and ending with the largest? a. group, supercluster, cluster b. cluster, supercluster, group c. group, cluster, supercluster d. cluster, group, supercluster e. supercluster, group, cluster 2. The most common type of galaxy found in a galaxy cluster is a ___________ galaxy. a. spiral b. giant elliptical c. giant irregular d. dwarf e. barred spiral 3. What does the large-scale structure of the universe look most like? a. a sponge with many large holes b. a loaf of wheat bread with many tiny holes c. a plate of flat noodles

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d. a jar of marbles e. a pizza with evenly distributed pepperoni 4. What is our cosmic address? a. Earth, Solar System, Milky Way, Local Group, Laniakea Supercluster b. Earth, Solar System, Andromeda, the Great Attractor, Local Group c. Earth, Local Group, Solar System, Milky Way, Cosmic Microwave Background d. Earth, Local Group, Solar System, Milky Way, Laniakea Supercluster e. Earth, Solar System, Andromeda, the Great Attractor, Laniakea Supercluster 5. Peculiar velocities are produced by a. erroneous redshifts. b. gravity. c. supernovae. d. eclipsing binary stars. e. interstellar winds.

6. The most common galaxy collections are called _______ and most of their members are _______ galaxies. a. clusters; spiral b. groups; dwarf c. superclusters; elliptical d. voids; peculiar e. walls; lenticular S0 7. How many times would our Local Group fit along the distance that separates it from the Virgo Cluster? a. 5 b. 10 c. 200 d. 1000 e. 2 8. Understanding the distribution of galaxies in the universe requires the construction of a 3D map where for each galaxy we need to know its position and a. mass. b. redshift. c. color. d. morphological type. e. star formation rate. 9. The peculiar velocity of a galaxy describes its motion relative to the a. Local Group. b. center of the Milky Way. c. center of the universe. d. Great Attractor. e. cosmic microwave background. 10. The figure below shows a small section of the Virgo galaxy cluster. The indicated galaxy can be classified as a. elliptical. b. peculiar. c. dwarf. d. ultrafaint. e. quasar. 11. Virgo galaxy cluster is at an estimated distance of 54 million ly. What is the average

recession speed of the cluster, assuming a Hubble constant of 70km/s/Mpc? a. 1,200 km/s b. 32,000 km/s c. 300 km/s d. 10,000 km/s e. 3800 km/s 12. Scientists estimate the following quantities for the Coma cluster of galaxies: the total mass of the cluster is Mtotal ~ 3.3 × 1015 M⊙, the total mass of all stars Mstars ~ 3 × 1013 M⊙, and the mass of the hot X-ray−emitting gas Mgas ~ 1 × 1014 M⊙. What is corresponding percentage of dark matter within the Coma cluster? a. 4 percent b. 25 percent c. 72 percent d. 96 percent e. There is no dark matter contribution.

13. Which of the following is not true about the Great Attractor? a. It is about 75 Mpc away. b. It has a mass of several thousand times the mass of the Milky Way. c. It is at the center of the Laniakea supercluster. d. It is in fact a black hole the size of a galaxy. e. It has gravitational effects on the motion of galaxies and groups of galaxies. 14. Choose the incorrect statement about the gas that fills the space between galaxies in a cluster? a. It is very hot and glows in X-rays. b. Its total mass far exceeds the combined mass of all the stars in the galaxy members of the cluster. c. Its particles move so fast that they easily escape the gravity of the cluster. d. It originates in stellar winds and/or it is stripped away from colliding galaxies. e. Its temperature gives us clues about the total gravitational mass of the cluster. . 15. Which of the following does not provide direct evidence for the existence of dark matter? a. the rotation curves of spiral galaxies b. the motions of galaxies in clusters c. the temperature of the diffuse intergalactic gas within clusters d. the gravitational lensing produced by galaxy clusters e. the changing fraction of peculiar galaxies as a function of redshift 16. Which of the following is not a way in which astronomers detect dark matter in clusters of galaxies? a. by determining the amount of mass necessary to gravitationally collapse clouds of gas to form the number of stars present b. by determining the amount of mass necessary to gravitationally hold onto the hot gas within galaxy clusters c. by determining the amount of mass necessary to gravitationally hold a cluster of galaxies together d. by determining the amount of mass necessary to gravitationally lens images of distant objects e. None of the above; all of these are ways that astronomers detect dark matter in galaxy clusters. 17. Which of the following components makes up the largest amount of normal matter in a typical large cluster of galaxies? a. supermassive black holes Copyright © 2015 Pearson Canada Inc.

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b. stars c. cold gas d. hot gas e. neutron and white dwarf stars If a galaxy is a member of a large cluster of galaxies, like the Coma cluster, the galaxy would have a typical velocity of 1,000 km/s. If the cluster is 10 Mpc in diameter, how long would it take the galaxy to cross from one side of the cluster to another? a. 10,000 years b. 1 million years c. 10 million years d. 100 million years e. 10 billion years What has the dominant role in defining the large-scale structure of the universe? a. supernovae from the first generation of stars b. gravity c. matter/antimatter annihilation d. magnetic fields e. electric force . Structure formation in our universe a. occurs for the largest structures first. b. occurs for the smallest structures first. c. begins on all spatial scales at the same time. d. begins after clusters form. e. begins with planets. Structure formation in the universe proceeds hierarchically, meaning that a. large objects collapse and then fragment to form smaller objects. b. large objects form at the same times as smaller objects. c. small objects collapse and then merge to form larger objects. d. only small objects form and are stable over time. e. normal matter collapses first and dark matter collapses later. . Quantum fluctuations in the early universe a. were the seeds that grew into today’s galaxies. b. are the reason dark matter exists. c. were made of small black holes. d. had no effect on the current structure of the universe. e. can be observed with radio telescopes.

23. The “Lambda-CDM” model combines the properties of __________ to explain the formation of structure in the universe. a. black holes and neutron stars b. dark energy and cold dark matter c. star formation and angular momentum d. nucleosynthesis and hot dark matter e. gravity and nuclear forces 24. Our current ideas on galaxy formation suggest that the visible parts of galaxies a. form first and are incorporated into dark matter halos later. b. form only in the densest parts of dark matter halos. c. can tell you the total size of the dark matter halo. d. can tell you everything about the formation history of that galaxy. e. spread out over distances larger than those of dark matter halos. 25. Why can’t dark matter halos collapse to be the same size as the visible parts of galaxies? a. Dark matter can’t dissipate its energy through radiation from collisions.

b. Dark matter is made mostly of miniâ&#x2C6;&#x2019;black holes. c. Dark matter has much more angular momentum. d. Dark matter annihilates when it begins to get that dense. e. Dark matter particles are too large to collapse that much. 26. The figure below shows snapshots taken from the Bolshoi simulation of the formation of the large-scale structure in the universe. Which one of these images shows the current structure of the universe? a. A b. B c. C d. D e. All of these occur at the same redshift, just in different regions of the universe.

27. Which of the following is not a possible candidate for dark matter? a. axions b. positrons c. photinos d. neutrinos e. WIMPS 28. Scientists think that neutrinos cannot be the dominant form of dark matter in the universe. Why? a. Neutrinos are an example of hot dark matter that could form large superclusters but not smaller structures. b. Neutrinos interact too strongly with ordinary matter. c. Neutrinos would decay over time and disappear, causing galaxies to fall apart. d. Neutrinos would not gravitationally lens background galaxies. e. Neutrinos are charged particles. 29. The small density variations that subsequently led to the formation of large-scale structure in the universe are thought to have formed a. from quantum fluctuations during inflation. b. due to the supernovae of the very first stars. c. at the end of the recombination epoch. d. as particle-antiparticle pairs annihilated. e. as supermassive black holes powered the first quasars. 30. The density of normal matter in the early universe was ______________ in the present epoch universe. a. much higher than the density of normal matter b. much lower than the density of normal matter c. about the same as the density of normal matter d. much higher than the density of dark matter e. about the same as the density of dark matter . 31. Which of the following is true about neutrinos? a. They are an example of cold dark matter. b. They are an example of hot dark matter. c. They have been theoretically predicted, yet never detected. d. They must be much more massive than the dark matter candidate called photino. e. They account for all the dark matter in the universe. 32. Which of the following statements about dark matter is incorrect?

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a. Cold and hot dark matter play differently on the formation of small and large-scale structure. b. Cold dark matter has the dominant role in the formation of individual galaxies. c. Dark matter most likely consists of elementary particles with no electric charge. d. Physicists use particle accelerators to look for hypothesized dark matter candidates. e. Hot dark matter has the dominant effect in the formation of individual galaxies. 33. If dark matter consisted of ordinary particles like protons and neutrons, a. the fraction of light elements produced in the Big Bang nucleosynthesis would have been severely different from what scientists observe. b. it wouldnâ&#x20AC;&#x2122;t have affected gravitationally the large scale structure of the universe. c. it would have prevented the expansion of the universe. d. scientists would easily be able to measure the decay of proton in the lab. e. it would manifest differently in individual galaxies and in large superclusters of galaxies.

34. Dark matter is essential in understanding the formation of the large scale structure in the universe in that it a. was clumpier than normal matter in the early universe. b. consists exclusively of antimatter particles. c. has a repulsive effect, just like the dark energy. d. explains the physics of black holes. e. cannot be made of elementary particles. 35. The best hypothesis about the nature of dark matter is that it consists of particles with no electric charge. Why would such particles have no electric charge? a. They cannot be more massive than an electron. b. If they did, they would emit photons as they move in external magnetic fields. c. Charged particles would have been all annihilated in particle-antiparticle collisions in the early universe. d. No elementary particle has electric charge. e. Charged particles formed only later inside stars. 36. How do the properties of the CMB give support to the existence of dark matter? a. The CMB has the same temperature as the cold dark matter. b. The faint glow of the CMB was actually produced by dark matter particles as they annihilated normal matter particles. c. The opaque CMB is essentially hiding the dark matter that existed earlier in the universe. d. The CMB is too smooth to account for the structure we observe in the universe. e. The observed spatial scale of CMB clumpiness perfectly matches that of the dark matter. 37. In the early universe, why were inhomogeneities in the distribution of normal matter much smaller than inhomogeneities in the dark matter? a. Normal matter is pushed away by supernova explosions. b. Magnetic fields smoothed the distribution of charged particles in the normal matter but not in dark matter. c. Dark matter particles were more massive than and cooled off before normal matter, thus dark matter fluctuations had a longer time over which to grow. d. Dark matter was 10 times more massive than normal matter. e. Radiation pressure affected normal matter but not dark matter. 38. The figure below shows snapshots taken from the Bolshoi simulation of the formation of the large-scale structure in the universe. Which one of these images represents the state of the universe at the highest redshift? a. A b. B

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c. C d. D e. All of these occur at the same redshift, just in different regions of the universe. 39. Telescopes like ALMA (working in the range 0.4-3 mm) and JWST (working in IR, in the range 0.6-28.5 micro-m) would help astronomers close a gap of observations that corresponds to the window a. z = 2−3, when the star formation rate peaked. b. z = 10−1000, between the epochs of recombination and reionization. c. z = 0−0.5, when there was a big change in the relative fraction of galaxies with peculiar morphologies. d. z > 1100, to directly observe the inflation epoch. e. such telescopes are actually designed to only explore planetary systems within the boundaries of our Milky Way. 40. The future James Webb telescope is designed to observe the most distant galaxies in the universe. It will observe them in a. UV. b. IR. c. visible. d. X-ray. e. radio. 41. The most distant galaxies detected at z ≈ 10 are best observed with __________ wavelengths of light. a. infrared b. visible c. X-ray d. gamma ray e. radio 42. At what redshift would a quasar’s emission line emitted at 121.6 nm show up at the “normal” wavelength of 486.1 nm of the Balmer Hβ line? a. 1 b. 2 c. 3 d. 5 e. 7 43. What would be the observed wavelength for the Balmer Hβ line emitted at 486.1 nm by a quasar at redshift z = 5? a. 2.9 µm b. 81.0 nm c. 21.0 cm d. 121.6 nm e. 1.2 µm 44. Reionization of the neutral gas in the universe occurred due to the a. decay of dark matter particles. b. emission of neutrinos by the first stars that formed. c. release of jets of charged particles from supermassive black holes. d. radiation from the first stars, supernovae, and black holes that formed. e. positron and electron annihilations. 45. The first stars formed in the universe had ___________ compared with the stars formed today. a. higher heavy element content and higher mass b. higher heavy element content and lower mass

c. lower heavy element content and higher mass d. lower heavy element content and lower mass e. higher mass and longer lifetimes 46. If astronomers discover a new ultrafaint galaxy, where would it most likely to be found? a. on its own, away from other galaxies b. a few billion light years away from Earth c. at high redshift d. in a large galaxy cluster e. orbiting the Milky Way

47. Which of the following does not describe the current view on the very first stars? a. They formed inside dark matter minihalos. b. There was no dust available to help the process of star formation. c. They must have been tens of times more massive than our Sun. d. The material from which they formed contained no elements more massive than lithium. e. The formed in large clusters with numerous members. 48. Which of the following best explains the difference between the heavy-element abundances seen in the first stars and those seen in stars that we observe today? a. Stars today have more heavy elements, because modern stars have higher masses, allowing them to create more heavy elements through nuclear fusion. b. Stars today have more heavy elements, because the gas that formed the current stars was enriched by the higher mass elements formed in previous generations of stars. c. Stars today have a fewer heavy elements, because they have been around long enough to use up the larger mass atoms. d. Stars today have a smaller abundance of heavy elements, because they haven’t been around long enough to make as many of the larger atoms. e. The stars that astronomers observe now are the first generation of stars. 49. Which of the following is not true about ultrafaint dwarf galaxies? a. They may be the remains of the first galaxies or first minihalos. b. They may offer support for the bottom-up scenario. c. They have been predicted but never been observed. d. They are dominated by dark matter. e. They have fewer stars than globular clusters do. 50. The processes of galaxy and star formation differ in all but one of the following aspects. Which one? a. Star formation follows a “top-down” sequence whereas galaxy formation involves a “bottom-up” sequence. b. Dark matter is essential in the formation of galaxies, but it is not involved in the formation of stars. c. Galaxy angular momentum originates in interactions of clumps whereas star angular momentum is caused by the turbulence of the original molecular clouds. d. The formation of a star is a very slow process whereas a galaxy forms in a very short timescale due to the huge difference in gravitational forces at play. e. When stars form, they acquire most of the mass of the collapsing system whereas in a Milky Way− like galaxy much of the matter remains distributed in a disk. 51. of these is not also true for galaxy formation? a. Angular momentum leads to the formation of a disk. b. For both stars and galaxies, the largest objects form first, with smaller objects coming together later. c. A gas cloud radiates energy, allowing it to collapse further than when it was hotter. d. Gravitational instability leads to collapse.

e. The original large gas cloud splits into smaller fragments, because areas with higher density also have greater gravitational pull. 52. Which of these lists shows the correct chronological order of the events listed, starting with the earliest and ending with the most recent? a. reionization, dark matter halos collapse, recombination, first galaxies are formed b. dark matter halos collapse, reionization, first galaxies are formed, recombination c. reionization, first galaxies are formed, dark matter halos collapse, reionization d. recombination, dark matter halos collapse, first galaxies are formed, reionization e. first galaxies are formed, dark matter halos collapse, reionization, recombination

53. Low-mass stars could form in the second generation because a. massive elements produced in the first stars coalesced into dust grains. b. they formed in minihalos of cold dark matter. c. gravitational waves led to the fragmentation of dark matter minihalos into microhalos. d. there was a lot more raw material available for star formation after the demise of the first stars. e. different types of fundamental forces controlled the formation of the first and second generation. 54. Choose the answer that does not correctly describe the second generation of stars. a. They could have form with low mass, because they formed in cooler environments. b. They contain small amounts of many massive elements. c. A few of the low-mass second-generation stars have been identified in the halo of the Milky Way. d. Their formation process is very different fromm that of the first generation stars. e. The low-mass second-generation stars are very hot and luminous and thus easy to detect. 55. Panel (b) of the figure below shows the enhanced infrared glow obtained after nearby stars and galaxies are subtracted from a standard Spitzer Space Telescope exposure. Scientists ascribe this faint signature to a. the CMB. b. the first stars and galaxies formed. c. GRBs and quasars. d. supernovae. e. our Sun. 56. What do astronomers predict will be the final state of our universe? a. a Big Crunch in which everything collapses back in on itself b. an ever-expanding universe filled with nothing but hydrogen and helium gas c. a universe that stops expanding and is filled with nothing but white dwarfs, neutron stars, and black holes d. an ever-expanding universe filled with photons and elementary particles e. a universe that stops expanding once enough stars become black holes 57. We expect the kinds of galaxies that we see at redshift of z â&#x2030;&#x2C6; 4 to be a. much like what we see today. b. smaller and much more irregular looking than today. c. smaller versions of what we see today. d. far more numerous but with fewer spiral galaxies. e. larger versions of what we see today. 58. Compared with what we see today, galaxies in the past were a. more ordered and more likely to have spiral structure. b. more ordered and less likely to have spiral structure.

c. messier and more likely to have spiral structure. d. messier and less likely to have spiral structure. e. exactly the same as they are today. 59. Which of these statements about galaxy clusters is true? a. Galaxy clusters do not require dark matter in order to form. b. Galaxy clusters are the largest structures in the universe. c. Small galaxy clusters form first and then merge together to form larger galaxy clusters. d. Galaxy clusters are evenly distributed throughout the universe. e. There are such large distances between galaxy clusters that they never actually run into each other.

60. Which probably formed last in the course of the evolution of the universe? a. a typical proton inside a water molecule on the Earth b. a helium atom in the surface of the Sun c. a typical star that is a member of a globular cluster star in our Milky Way d. the Milky Way e. the Virgo Supercluster 61. Cosmologists estimate that the last stars will form about ________ years from now. a. 109 b. 1014 c. 1065 d. 1098 e. 10100 62. Scientists estimate that, in the distant cosmic future, before the universe becomes filled exclusively with elementary particles, the last large concentrations of mass will be a. white dwarfs. b. neutron stars. c. black holes. d. brown dwarfs. e. ultrafaint galaxies. 63. If dark energy is embedded within the vacuum of space, then the best places to study it would probably be the a. spiral galaxies. b. interacting, peculiar galaxies. c. cosmic walls and filaments. d. cosmic voids. e. clusters of galaxies. 64. The largest cosmic supervoid ever discovered spans an estimated length of about 1.8 Gly. How many Milky Way galaxies would fit side-to-side within this apparently empty region in space? a. 1.8 b. 18 c. 180 d. 18,000 e. 1.8 Ă&#x2014; 109 65. Which of the following is not likely to happen when two spiral galaxies collide? a. A more massive elliptical galaxy might form out of the merger. b. The two supermassive black holes at their centers could form a binary black hole system. c. Individual stars collide to create many supernovae. d. A burst of star formation will occur in the merged galaxy. e. The cold gas in the merged galaxy might be blown away by supernovae.

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66. By measuring the star formation rate in galaxies as a function of their redshift, we have learned that the average star formation rate in galaxies peaked approximately _________ years ago. a. 1 billion b. 3 billion c. 5 billion d. 7 billion e. 11 billion

67. How has the fraction of galaxies with peculiar morphologies evolved from z ≈ 0.4 to the present epoch? a. About 10 percent of today’s galaxies are peculiar, whereas at z ≈ 0.4 the fraction increases to more than half. b. The fraction has been the same 50 percent over the last 4−5 billion years. c. At the present epoch there are far more interacting galaxies than when the universe was about 9−10 billion years old. d. The fraction has been unchanged 10 percent over the last 4−5 billion years.

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e. There are no peculiar galaxies today, whereas at z ≈ 0.4 the fraction is close to 10 percent. Which of the following may not necessarily be indicative of a “bottom-up” scenario for galaxy formation? a. Galaxies observed at very high redshift are typically 20 times smaller than the Milky Way. b. There are many more peculiar galaxies at high redshift compared with those at low redshift. c. Our own galaxy, the Milky Way, is classified as a barred spiral. d. Quasars exist even at redshifts exceeding z = 7. e. The star formation rate has changed over cosmological time. Ignoring the effect of redshift, we expect the galaxies that we see at a redshift of z = 3 will be _____________ than galaxies today. a. more irregular and redder b. larger and redder c. smaller and bluer d. smaller and redder e. larger and bluer Which of the following is not a reason that supercomputer cosmological simulations like Bolshoi are extremely valuable? a. They produce images aesthetically suitable for the general public. b. Comparing simulations to actual observational data sets constraints on fundamental parameters of the universe. c. They can trace the evolution of both visible and invisible matter in the universe. d. They can make predictions that can be cross-checked against observations. e. They allow the study of a sequential process of galaxy evolution. Which of the following is not a consequence of intergalactic encounters and mergers? a. the rate of star formation b. the activity of the galactic supermassive black holes c. the formation of supermassive black holes d. the changing proportions of various morphological types with the age of the universe e. the cosmological recession of galaxies

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72. The expansion of the universe will eventually render the CMB invisible because its photons will a. have wavelengths that will exceed than the size of the observable universe. b. be swamped by the light from the ever-increasing star-formation rates in the universe. c. not have enough energy to escape the gravity of degenerate stellar remnants. d. all combine and again produce pairs of massive particles. e. not escape the strong gravity of supermassive black holes the size of galaxy clusters.

73. Which of these statements about black holes in the early universe is not true? a. Supermassive black holes affected the star formation rates in early galaxies. b. The growth of supermassive black holes is likely linked with galaxy mergers. c. The first generation of stars had high enough masses to leave black holes behind after exploding as supernovae. d. The black holes in the early universe should have been larger than those seen today. e. Supermassive black holes may have formed from mergers of smaller black holes.

SHORT ANSWER 1. Describe the large-scale structure of the universe. 2. In the context of the galaxy clusters, rank the proportions of stellar, intergalactic (intracluster) X-ray− emitting gas, and dark matter mass. 3. Studying galaxies of various morphological types, scientists have estimated equivalent mass-to-light ratios (M/L) of about 1−30 in solar units (1 M⊙/ 1 L⊙), being lower for spiral and higher for elliptical galaxies. In galaxy clusters, however, the typical total mass-to-light ratio is estimated in the range 300−600 (M⊙/L⊙). What is the implication of these numbers?

4. Explain what the arcs seen in the Hubble Space Telescope image shown below represent. 5. Scientists quantified the following amounts of mass for the Coma cluster of galaxies: the total mass of the cluster is Mtotal ~ 3.3 × 1015 M⊙, the total mass of all stars Mstars ~ 3 × 1013 M⊙, and the mass of the hot X-ray−emitting gas Mgas ~ 1 × 1014 M⊙. What is corresponding percentage of dark matter within the Coma cluster? 6. Use Hubble’s law to explain how measurements of redshift help astronomers map out the large-scale structure of the universe. 7. Describe two ways in which you could measure the mass of a galaxy cluster. 8. How do we know how fast the Milky Way is moving relative to the local universe? What

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are we moving toward, and what do we think is mostly responsible for this motion? 9. What is the fundamental difference between the two types of dark matter candidates? List an example of each type. 10. Why do astronomers think that cold dark matter (as opposed to hot dark matter) is the primary component of dark matter in galaxies? 11. How are the observed properties of the CMB leading to the idea that dark matter plays a crucial role in the formation of structure in the universe? 12. Explain why the physics of formation of the second generation stars is even more complex than that of the first generation. 13. Based on the figure and chart shown below, roughly estimate the range of redshift defining (i.e., bracketing) the epoch of reionization. 14. Explain why a galaxy can collapse to a much smaller size than its dark matter halo. 15. What are some other possible candidates (macroscopic objects) for dark matter besides elementary particles? 16. What is the only identified form of dark matter? 17. What would be the observed wavelength for the Lyman-alpha emission at 121.6 nm from the distant galaxy at redshift z = 8.68? 18. An astronomer wants to study the epoch of reionization, which occurred roughly in the range of 6 < z < 11. What range of wavelength must the astronomer be able to detect corresponding to light emitted at 500nm? 19. In the immediate aftermath of the recombination epoch, neutral hydrogen produced 21-cm photons. What would be the corresponding observed wavelength (at the present epoch) for such photons emitted at redshift z ~ 100? 20. The Hubble Space Telescope is equipped with an infrared camera WFC3/IR installed on it in 2009 during the last servicing mission, sensitive to photons up to about 1.7 Âľm. It is estimated that the youngest (i.e., most distant) galaxy detected in the Hubble XDF (eXtreme Deep Field; see the images in the figure shown below) existed just 450 million years after the Big Bang. What is the emitted wavelength from that galaxy that was still detectable with the aforementioned infrared camera? (Note that the redshift is z ~ 10.2 when the universe has the indicated very young age.)

21. The Mid-Infrared Instrument (MIRI) that will be attached to the James Webb Space Telescope covers the wavelength range of 5 to 28 microns. Calculate over what redshift range it can detect the 500 nm photons emitted by galaxies. 22. What was temperature and wavelength of the cosmic background blackbody signature at the epoch of reionization, about 400 million years after Big Bang?

23. Explain why dark matter dominates the halos of galaxies but does not play a role in the formation of small structures (stars, planets, etc.) within galaxies. 24. What stage in the evolution of the universe is coined as “the epoch of reionization,” and what is the significance of this name? 25. What was the cooling mechanism that allowed the first stars to form? 26. Explain and contrast the top-down vs. bottom-up scenarios for star, galaxy, and galaxy cluster formation, respectively. 27. One of the most distant galaxies observed to date shows a redshift z = 8.68, whereas one of the most distant candidates (not fully confirmed yet) is a galaxy at a redshift of about z ~ 10.7. Why are such discoveries, rare for now, so exciting? 28. Outline a few fundamental differences between the formation of the very first stars and that of the second or subsequent generations. 29. How do astronomers explain the formation of elliptical galaxies? 30. Explain how computer simulations of structure formation and observations of the structure in the universe today can help astronomers determine the nature of dark matter. 31. Based on the snapshot of a Bolshoi cosmological simulation in the figure below, roughly estimate the size of the largest void captured in the frame. Note that each side of the square field in the simulation represents 89 Mpc. 32. Explain why the Bullet Cluster is considered a strong example for the existence of dark matter, based on the figure below.

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