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

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Chapter 21: The Expanding Universe LEARNING OBJECTIVES Define the bold-faced vocabulary terms within the chapter. 21.1 The Cosmological Principle Compare and contrast the meaning of homogenous and isotropic. Multiple Choice: 1, 2, 4, 10 Illustrate the meaning of “homogenous and isotropic.” Multiple Choice: 8 Short Answer: 1 Explain how the cosmological principle implies that there is no center of the universe. Illustrate why observers in a uniformly expanding space will all observe Hubble expansion. Multiple Choice: 3, 5, 6, 9, 11, 36 Short Answer: 2, 3, 4, 6, 7 Relate redshift to look-back time. Multiple Choice: 7

Short Answer: 5, 8 21.2 The Universe Began in the Big Bang Explain why Hubble expansion observed today implies the universe was smaller and hotter in the past. Multiple Choice: 29, 30, 31, 37, 56 Distinguish between Hubble expansion arising from the expansion of space and its arising from an explosion flinging debris through space. Multiple Choice: 32, 33, 34, 35 Short Answer: 14 21.3 Expansion Is Described with a Scale Factor Characterize how the scale factor changes with time. Multiple Choice: 45, 46, 47 Short Answer: 18, 19 Illustrate how expanding space leads to the redshift of light from distant objects. 21.4 Astronomers Observe Cosmic Microwave Background Radiation Illustrate why we expect the universe to be filled with a cosmic microwave background. Multiple Choice: 55, 71 Short Answer: 20, 22 Relate the image seen in the cosmic microwave background to the epoch of recombination of hydrogen. Multiple Choice: 51, 58, 59, 70 Short Answer: 21, 23, 24, 25, 26, 27 Describe the observed characteristics of the cosmic microwave background. Multiple Choice: 49, 50, 60, 61, 62, 64, 65, 68 Short Answer: 28, 29, 30 Characterize the conditions in the early universe based on the currently observed cosmic microwave background. Multiple Choice: 48, 52, 53, 54, 57, 66, 67, 69, 72 Working It Out 21.1 Use Hubbleâ&#x20AC;&#x2122;s law to estimate the age of the universe. Multiple Choice: 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28

Short Answer: 9, 10, 11, 12, 13 Working It Out 21.2 Relate redshift to scale factor. Multiple Choice: 38, 39, 40, 41, 42, 43, 44 Short Answer: 16, 17 Distinguish between different sources of classical and relativistic redshift.

Short Answer: 15

MULTIPLE CHOICE 1. What do astronomers mean when they say that the universe is homogeneous? a. All stars in all galaxies have planetary systems just like ours. b. The universe looks exactly the same no matter what direction you look. c. Galaxies are generally distributed similarly throughout the universe. d. Generally speaking, there is little difference between conditions on Earth, in the Sun, or in outer space. e. The universe looks the same at all times in its history. 2. What do astronomers mean when they say that the universe is isotropic? a. Far away parts of the universe look just like nearby parts. b. All galaxies are spiral galaxies like our own. c. Intergalactic gas has the same density everywhere in the universe. d. The laws of physics apply everywhere in the universe. e. The universe looks the same no matter what direction you look. 3. According to Hubble’s law, as the distance of a galaxy __________ its __________ increases. a. increases; luminosity b. increases; recessional velocity c. decreases; luminosity d. decreases; recessional velocity e. decreases; peculiar velocity 4. If we lived in a galaxy 1 billion light−years from our own, what would we see? a. a universe 1 billion years younger than ours b. a universe 1 billion years older than ours c. much the same universe we see here d. a universe expanding at a slower rate than we see from Earth e. a universe expanding at a faster rate than we see from Earth 5. The spectra of most galaxies tell us that a. most galaxies appear to be moving away from us. b. their light comes predominantly from objects other than stars.

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c. most galaxies contain clouds of gas that are absorbing their favorite wavelengths. d. galaxies in the past rotated at a faster rate than they do today. e. galaxies are rushing through space at high speeds. 6. Why are some galaxies’ spectra blueshifted rather than redshifted? a. Some distant galaxies are gravitationally lensed. b. Some distant galaxies show the universe was contracting before the Big Bang started. c. Some nearby galaxies have vigorous star formation and are much bluer than others. d. Some distant galaxies have AGN at their centers. e. For some nearby galaxies the attraction of Milky Way dominates over the Hubble expansion of space. 7. If the distance of a galaxy at a redshift z = 0.5 is 1,900 Mpc, how many years back into the past are we looking when we observe this galaxy? a. 500 million years b. 2 billion years c. 6 billion years d. 9 billion years e. 10 billion years 8. The cosmological constant was somehow “artificially” introduced by Einstein in order to a. make the universe stationary. b. explain the nature of dark matter. c. explain the riddle of black holes. d. explain the nature of dark energy. e. create a more interesting mathematical solution to his equations 9. The spectrum of the galaxy NGC 7512 reveals a receding velocity of about 7000 km/s. An observer in that galaxy takes a spectrum of the Milky Way and measures __________________________. a. the same 7000 km/s receding speed b. only 1000 km/s, because for that observer the Hubble expansion is a lot slower c. something that we cannot possibly know, because the laws of physics apply only within the Milky Way d. 23,000 km/s, because the speed of light has a different value for that observer e. no relative motion, because we are in fact wrong; the universe is static end eternal 10. In an imaginary universe, astronomers find that there are thousands of galaxies within a few million light years in all directions, but beyond those galaxies there is nothing but empty space. Such a universe would be a. isotropic and homogeneous. b. isotropic but not homogenous. c. homogeneous but not isotropic. d. neither homogeneous nor isotropic. e. lacking any evidence for the Big Bang. 11. You measure the redshift of a distant galaxy and find, using Hubble’s law and assuming a Hubble constant of 70 km/s/Mpc, that its distance is 1 billion ly. Imagine that an observer in that galaxy is measuring the recession speed of the Milky Way while you measure. What would be the speed that the remote alien observer would record? a. 700 km/s b. 21,500 km/s c. 3,400 km/s d. 10,700 km/s e. 6,300 km/s 12. Astronomers use galactic redshift as a measure of a. gravity. b. luminosity. c. velocity.

d. mass. e. distance. 13. The inverse of the value of H0 gives a measurement in a unit of a. time. b. mass. c. density. d. size. e. luminosity. 14. What would you predict for the recession velocity of a galaxy whose distance (measured with the help of Type Ia supernovae) is 42 Mpc? a. 2940 km/s b. 1.42 km/s c. 205,800 km/s d. 25,000 km/s e. 386 km/s

15. Estimate the time it takes two galaxies to reach a presently measured separation of 55 Mpc. a. 13.9 billion years b. 250 million years c. 4.6 billion years d. less than a second e. 27 billion years 16. If a galaxy has an apparent velocity of 700 km/s, what is its distance if the Hubble constant is 70 km/s/Mpc? a. 10 Mpc b. 70 Mpc c. 100 Mpc d. 700 Mpc e. 1,000 Mpc 17. If the distance of a galaxy is 10 Mpc, what is its recessional velocity if the Hubble constant is 70 km/s/Mpc? a. 700 km/s b. 1,000 km/s c. 3,500 km/s d. 5,000 km/s e. 7,000 km/s 18. Hubble originally estimated the “Hubble constant” to be about 500 km/s/Mpc. What age of the universe would such a number imply? a. 2 billion years b. 13.8 billion years c. 16 billion years d. 250 million years e. 500 million years . 19. Which of the following pairs of numbers for recession velocity of galaxies and distance to galaxies is not correct? a. 2,100 km/s, 30 Mpc b. 4,200 km/s, 60 Mpc c. 7,000 km/s, 100 Mpc d. 5,600 km/s, 80 Mpc e. 6,100 km/s, 340 Mpc 20. You observe the following three galaxies and measure their respective recession velocities:

(A, 2,100 km/s); (B, 4,400 km/s); and (C, 3,050 km/s). Which of the following must be true about these galaxies? a. A is smaller than B. b. A has more star formation than C. c. B has more stars than C. d. B is farther than A. e. They are all members of the Local Group. 21. If the slope of the graph v vs. D is Ho, the slope of the D vs. v graph is the a. age of the universe. b. cosmological constant. c. scaling factor of the universe. d. temperature of the CMB. e. amount of dark energy in the universe.

22. If the Hubble constant had a value that was half of its current measured value of 70 km/s/Mpc, the age of the universe would be about a. 7 billion years. b. 14 billion years. c. 22 billion years. d. 28 billion years. e. 33 billion years. 23. Which of the following would not immediately rule out a Hubble constant of 300 km/s/Mpc? a. the age of the Sun b. the age of the globular clusters in the Milky Way c. the age of the coolest known white dwarfs d. the age of a main sequence star 50 times more massive than our Sun e. the age of our Milky Way Galaxy 24. A Hubble constant of 70 km/s/Mpc is the same as a. 0.072 Gyr−1. b. 13.9 km/s/ly. c. 7 × 10−5 km/s/ly. d. 0.014 km/s/ly. e. 0.014 Gyr−1. 25. Galaxy peculiar velocities are typically about 300 km/s. How far away do you have to look in order to see galaxies recessional velocities that are 10 times this peculiar velocity? a. 12 Mpc b. 25 Mly c. 37 Mpc d. 43 Mpc e. 52 Mpc 26. If you found a galaxy with an Hα emission line that had a wavelength of 756.3 nm, what would be the galaxy’s distance if the Hubble constant was 70 km/s/Mpc? (Note that the rest wavelength of the Hα emission line is 656.3 nm.) a. 650 Mpc b. 760 Mpc c. 3,200 Mpc

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d. 6,400 Mpc e. 7,600 Mpc If the spectrum of a distant galaxy is observed to have a calcium K absorption line that occurs at a wavelength of 500.4 nm, what is this galaxy’s distance if the rest wavelength of this absorption line is 393.4 nm? Assume the Hubble constant is 70 km/s/Mpc. a. 720 Mpc b. 850 Mpc c. 1,200 Mpc d. 2,500 Mpc e. 3,700 Mpc In the figure shown below, the upper spectrum is from hydrogen at rest in a laboratory, and the lower spectrum is from a galaxy. How far away is this galaxy? a. 110 Mpc b. 170 Mpc c. 230 Mpc d. 280 Mpc e. 340 Mpc Galaxies move away from us in all directions because a. the force of gravity increases with distance. b. the force of gravity weakens with distance. c. space is expanding. d. our galaxy has expelled all other galaxies. e. we are at the center of the expansion of the universe. Hubble’s constant, H0, represents the a. rate of expansion of the universe. b. speed at which galaxies are moving away from us. c. time it takes a galaxy to move twice as far away from us. d. size of the universe. e. amount of time since the Solar System formed.. Choose the incorrect statement about Hubble’s law. a. It allows us to measure distances to remote galaxies. b. It is one fundamental piece of evidence supporting the expansion of the universe. c. It provides information about the age of the universe. d. It applies only to nearby galaxies, within the Local Group. e. It is essentially a linear proportionality between recession velocity and distance for galaxies. Where in the universe did the Big Bang take place? a. near the Milky Way Galaxy b. near the Virgo cluster c. near some unknown location on the other side of the universe d. everywhere in the universe e. at the center of the universe, not too far from the center of the cosmic background radiation Hubble’s law is written in a mathematical form as a. v × D = Ho. b. v × D = 1/Ho. c. v = Ho × D. d. v × Ho = D.

e. D/v = Ho. 34. Is dark energy responsible for the expansion of the universe? a. No. The expansion would happen without dark energy, but dark energy is causing the expansion rate to decrease. b. Yes. Dark energy is currently the driving force in the universe’s expansion.

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c. No. Dark energy is only responsible for the observed rapid motions of stars within galaxies. d. No. The expansion would happen without dark energy, but dark energy is causing the expansion rate to increase. e. No. The dark energy has no effect on the expansion. 35. The apparent recessional velocities of galaxies at large distances are due mainly to a. the actual motions of the galaxies through space. b. the motion of our Sun around the galactic center. c. a continuously increasing scaling factor of the universe. d. the relativistic jets launched by supermassive black holes. e. incorrect interpretation of spectra from galaxies.

36. An expanding universe a. was first predicted by the general theory of relativity. b. was first discovered observationally by Hubble and afterwards rejected on theoretical grounds. c. is just an abstract and meaningless mathematical solution to a purely theoretical equation in relativity. d. is at odds with the cosmological principle. e. it is not consistent with the predictions of the Big Bang model. 37. If you measured the distances and recessional velocities for a sample of galaxies and plotted the data to get the figure shown below, what value would you derive for the Hubble constant? a. 10 km/s/Mpc b. 50 km/s/Mpc c. 70 km/s/Mpc d. 100 km/s/Mpc e. 500 km/s/Mpc 38. Scientists indicate that the first stars probably formed at a redshift z ~ 20. At that time the universe was about a. 5 percent of its current size. b. 50 percent of Earth’s size. c. as big as an atom. d. about 100 AU across. e. the size of a grapefruit. 39. The universe was 10 percent its current size when light left objects observed now at redshift a. 1. b. 3. c. 6. d. 9. e. 20. 40. What is the correct interpretation of a redshift larger than 1? a. The object is moving faster than the speed of light. b. The universe has more than doubled in size since the light from that object was emitted. c. The object has an extremely large peculiar velocity. d. The light was shifted to longer wavelengths from gravitational radiation. e. The rate of expansion of the universe is increasing. 41. When we look at galaxies in the universe and measure their star formation rates, we find that galaxies at redshifts z ≈ 1 have higher star formation rates than they do now. At that time, the universe was __________ times the size it is today. Copyright © 2015 Pearson Canada Inc.

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a. 0.1 b. 0.2 c. 0.5 d. 0.7 e. 0.9 42. Distant galaxies we can see today with a redshift of z ≈ 6 emitted their light when the universe was a. five times smaller than it is today. b. six times smaller than it is today. c. seven times smaller than it is today. d. eight times smaller than it is today. e. the same size as it is today.

43. The CMB is a snapshot of the radiation in the universe at a redshift of z ≈ 1,000 when the universe was about a. 1,000 times smaller than it is today. b. 10 times smaller than it is today. c. two times smaller than it is today. d. the same size as it is today. e. 10 times larger than it is today. 44. The record for the most distant galaxy in the universe was recently reported with a redshift of z = 8.68. Compared with the current size of the universe, what was its size when the light from that galaxy started its long journey to us? a. about 10 times smaller b. about 50 percent smaller c. about 0.001 percent smaller d. about 99 percent smaller e. about 250 percent bigger 45. Which of the following are changing as the universe is expanding? a. the laws of physics b. the sizes of atoms c. the sizes of planetary systems d. the cosmological distances e. the diameters of stars and galaxies 46. Will the Sun get larger over many billions of years? a. Yes, because of changes taking place in its interior. b. Yes, because the rate of expansion of the universe is increasing. c. No, because the Earth is at center of the universe’s expansion. d. Yes, because the expansion of the universe is pulling the Sun apart. e. No. It has always been the same size. 47. It is possible for a galaxy to have an apparent velocity greater than the speed of light. This means that the galaxy a. has an active nucleus capable of producing relativistic jets. b. is approaching us and the measured speed is a mere artifact of projecting its velocity along the line of sight. c. has been ejected at tremendous speed by the Big Bang. d. is being temporarily accelerated by large numbers of simultaneous supernovae blasts. e. it is being carried by the expansion of the universe. 48. Which of the following is not a prediction of the standard Big Bang theory that has been successfully verified by observations? a. The universe is expanding. b. The most distant galaxies are redder because they are older. Copyright © 2015 Pearson Canada Inc.

c. Helium and lithium were made as the universe cooled after the initial Big Bang. d. The early universe was very hot and dense. e. The most distant galaxies are redder because their light has been stretched during the time it took for the light to reach Earth. 49. In the early 1960s, physicists Penzias and Wilson detected a persistent noise at a wavelength of about 1 mm in their radio telescope that came from all directions in the sky due to a. synchrotron emission from the Crab Nebula. b. emission from newly formed stars in the Orion Nebula. c. cellphone usage. d. photons left over from the Big Bang. e. television and radio broadcasting.

50. The temperature of the CMB is hotter on one side of the sky than on the other by approximately 3 mK. What does this tell us? a. The Earth has a peculiar velocity of about 8,000 km/s with respect to the CMB. b. The Earth has a peculiar velocity of about 400 km/s with respect to the CMB. c. The Earth is near the center of the universe’s expansion but not exactly at the middle. d. The universe is expanding faster on one side of us than on the other. e. The universe is homogeneous but not isotropic. 51. The oldest photons we detect in the universe come from a. distant quasars. b. the first generations of stars. c. the most distant galaxies. d. the epoch of recombination. e. the first supernovae. 52. The cosmic microwave background radiation was emitted when the universe had a size about 1/1000 of today’s value. What was the temperature of the microwave background radiation at the epoch of recombination? a. 30 K b. 300 K c. 3000 K d. 30,000 K e. 300,000 K 53. The existence of the cosmic background radiation tells us that the early universe was a. much hotter than it is today. b. much colder than it is today. c. composed entirely of radiation at early times. d. composed entirely of stars at early times. e. about the same temperature as today but much more dense. 54. After the Big Bang, as the universe cooled and protons and electrons combined, what important consequence happened? a. Protons and neutrons combined to form nuclei such as deuterium and helium. b. Neutrinos ceased to interact with normal matter. c. Dark matter ceased to interact with normal matter. d. Photons began to travel freely through the universe. e. Lithium and other light elements were formed by the fusion of hydrogen and helium. 55. Does the temperature of the cosmic background radiation by itself tell us anything significant about the age of the universe? a. Yes, since it was produced at a redshift of approximately 1,000. b. No, we still need to know the Hubble constant to know the universe’s age. c. No, the temperature does not, but the magnitude of temperature variations in the CMB does tell us the age.

d. Yes, in combination with information on cosmic nucleosynthesis. e. No, the CMB formed at a wide variety of times and gives no information on the age of the whole universe. 56. Choose the incorrect statement about the CMB. a. It is nearly isotropic. b. It is a fundamental confirmation of the Big Bang theory. c. It is a thermal signature described by a temperature of about 3K. d. It was discovered accidentally in the 1960s. e. It is thought to be produced by the first generations of stellar black holes.

57. The CMB can be regarded as a “wall” beyond which we cannot see light because a. photons couldn’t leave the hot plasma before the recombination period. b. we haven’t discovered the technology to detect light from earlier epochs. c. galaxies absorb all the photons from earliest times, closer to the Big Bang. d. there existed only massive particles within the universe in the first 380,000 years of existence and no photons. e. behind the CMB “wall” there is a huge black hole that doesn’t allow light to escape. 58. If the temperature of the CMB changes with redshift z as T = T0(1 + z), where T0 is the currently measured 2.73K, what is the redshift corresponding to the time when the photons first escaped from the 3000 K hot bubble of ionized material? a. about 10 b. about 100 c. about 1 d. about 1000 e. about 0.5 59. How many times smaller was the universe when the currently observed CMB photons started their journey to us? a. 1/1000 b. 1/10 c. 1/100 d. 1/10 5 e. 0.001 percent 60. The COBE microwave map shown in the figure below seems to indicate that one part of the sky is 0.003 K warmer than the other. What is the cause of such an apparent anisotropy? a. Earth and Sun are moving at 368 km/s in the direction of the constellation Crater relative to the CMB frame. b. The map was obtained when the Sun was at its peak of activity within a given 11−year cycle. c. It is due to interference with the many microwave ovens people use in homes. d. The boundaries between the warmer and cooler areas are sites of strong supernova activity. e. It indicates that galaxies could form in only half of the universe. 61. The apparently “grainy” CMB distribution shown in the WMAP in the figure below represents temperature fluctuations of about a. 0.001 percent. b. 0.1 percent. c. 10 percent. d. 50 percent. e. 27.4 percent. 62. The CMB fluctuations seen in the WMAP temperature distribution measures are of crucial Copyright © 2015 Pearson Canada Inc.

importance in that a. they prove that the cosmological principle is incorrect, the universe is in fact anisotropic. b. they reveal the signatures of the large mass concentrations where subsequent galaxies and clusters of galaxies formed. c. they reveal the technical limitation of the detectors on board the WMAP satellite. d. they give us clues about the black hole evaporation happening in the early universe. e. they emphasize the limited value of general relativity. 63. The CMB fluctuations of 0.001 percent seen in the WMAP sky map are due to a. gravitational redshifts. b. technical artifacts. c. faulty instrumentation. d. Hubble expansion. e. explosive supernovae. 64. The CMB spectrum shown in the figure below is a. a thermal spectrum. b. an emission line spectrum. c. an absorption line spectrum. d. identical to the spectrum of our Sun. e. blueshifted into the microwaves domain. 65. Why is it not possible to look all the way back to the Big Bang itself? a. Photons are not produced until the stars begin to shine at a redshift of z ≈ 20. b. From redshifts of z = 0 to 100, photons are gravitationally lensed by the dark matter in the universe. c. At redshifts of z > 1,000, most of the photons are blocked by large amounts of cold gas and dust. d. For redshifts of z > 1,000, photons cannot travel freely because they easily interact with individual protons and electrons in the universe. e. Photons from the Big Bang would be so strongly redshifted that we could never detect them. 66. If the wavelength of the background radiation peaked at 1 µm at the time of recombination, how old was the universe then compared with its age today? a. one second old b. 1/100th of a second old c. 1/1,000th of a year old d. 3,000 years old e. several hundred thousand years old 67. The current temperature of the cosmic background radiation of 2.73 K means that the peak of its spectrum occurs at a wavelength of a. 0.1 µm. b. 1 µm. c. 10 µm. d. 100 µm. e. 1,000 µm. 68. Why did the Big Bang nucleosynthesis only produces elements less massive than lithium and beryllium? a. The universe expanded and cooled rapidly. b. The universe was never hot enough for nucleosythesis by fusion before stars formed. c. There was no black hole to provide sufficient energy for advanced nucleosythesis. d. The laws of physics do not allow the formation of massive nuclei outside stars. e. More massive elements did form, but they decayed very fast into lighter ones. 69. Which of the following objects would be the oldest? Copyright © 2015 Pearson Canada Inc.

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a. b. c. d. e.

a 4000K WD the Sun the CMB a 20 solar mass main sequence star a halo star with 1/250 heavy element abundance relative to the Sun’s

70. Which of the following scientists is not directly connected to the prediction or discovery of the CMB? a. Arno Penzias b. Robert Wilson c. George Gamow d. Robert Dicke e. Georges Lemaître 71. Which of the following particles was not produced in the immediate aftermath of the Big Bang? a. hydrogen b. helium c. protons d. iron e. photons

SHORT ANSWER 1. Describe the two assumptions regarding the universe that the cosmological principle makes.

2. We see the universe around us expanding, at a rate of 70 km/s/Mpc. If you were an astronomer living today in a galaxy that was located 1 billion light years away from us, at what rate would you see the galaxies moving away from you? 3. Does the expansion of the universe make the Sun bigger? What about the Milky Way? Why or why not? 4. Why did Einstein call his cosmological constant his “biggest blunder”? 5. The spectrum of a galaxy is observed to have an Hα emission line at a wavelength of 928.7 nm. What is its redshift? Note that the rest wavelength of the Hα emission line is 656.3 nm. 6. Does Hubble’s law imply that our galaxy is sitting at the center of the universe? Explain. 7. Imagine a balloon that you can inflate to visualize the expansion of the universe. The space is symbolized by the surface of the balloon. You use a marker to draw/paint galaxies on its outside surface and you start pumping out air inside the balloon. How would this model conform or not with the correct view of an expanding universe?

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8. Explain the difference between the universe and the observable universe. 9. The spectrum of a galaxy is observed to have an Hα emission line at a wavelength of 856.3 nm. What is its distance if the Hubble constant is 70 km/s/Mpc? (Note that the rest wavelength of the Hα emission line is 656.3 nm.) 10. Employing Hubble’s law, calculate the distance to the Andromeda Galaxy, which is moving at 110 km/s. The directly measured distance to Andromeda is 2.5 million light−years. How would the two numbers agree or disagree. Explain. 11. If the oldest known globular clusters are about 13 billion years old, how is this constraining the Hubble constant value? 12. If the Hubble constant were equal to 50 km/s/Mpc, what would the approximate age of the universe (the Hubble time) be, assuming that the expansion rate has stayed approximately constant over time? Note that 1 Mpc = 3.086 × 1019 km and 1 year = 3.154 × 107 s. 13. Give two examples of very old objects that could help astronomers set a lower limit on the age of the universe. 14. Why is the typical visual depiction of the Big Bang in movies and television shows scientifically incorrect? 15. Explain the different types of redshift you encountered in this chapter. 16. The Hubble Space Telescope can be used to study galaxies at a redshift equal to 2. How much has the universe expanded since that light was emitted from these galaxies? 17. You observe a distant quasar in which the Lyman alpha line (Lα) of hydrogen (rest wavelength = 121.6 nm) is found at a wavelength of 547.2 nm. When the light from this quasar was emitted, how large was the universe compared to its current size? 18. What does the value of RU, the scale factor of the universe, tell us? 19. In the late 1940s, various scientists hypothesized the existence of a background radiation, a leftover signature from the Big Bang, although they also predicted a rather cool temperature for it, in the range of 5−50K. Why did they expect such a cold radiation to permeate the universe? 20. Briefly explain how an accurate determination of Hubbleconstant has improved our understanding of cosmology. 21. Why is the “recombination” term used to describe the epoch when the universe became

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transparent to photons sort of a misnomer? 22. What are the three different tests that support the Big Bang cosmology? 23. If the temperature of the CMB changes with redshift z as T = T0(1 + z), what is the redshift corresponding to the time when the photons escaped from the hot bubble of ionized material? 24. If the temperature of the CMB changes with redshift z as T = T0(1 + z), and the recombination happened when the universe was about 1,000 times smaller than at the present time, what was the temperature at the time the universe became transparent to photons? 25. If the temperature of the CMB changes with redshift z as T = T0 (1 + z), what was the peak wavelength of this thermal/Plank signature when the universe was 1 percent of its current size? 26. What important event in the universe’s early history marked the creation of the cosmic background radiation? 27. Show in a graph format how the scaling factor Ru changes with redshift. 28. The cosmic microwave background (CMB) has a temperature of approximately 2.73 K and a Planck blackbody spectrum. Calculate the wavelength where the CMB spectrum peaks. 29. What is the significance of the 0.001 percent fluctuations detected in the CMP map by modern satellites like WMPA and Plank, as in the figure shown below? 30. The COBE and WMAP satellites detected fluctuations in the CMB. On average, how big were these fluctuations, and what do they that tell us about the universe at a redshift of z = 1,000?

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