Chapter 17: Galaxies

Section: Introduction

1. Suppose the Milky Way Galaxy is 1 of a 1000 billion galaxies and they similarly have, on average, 200 billion stars each. How many stars is that?

A) 2  10¹⁹

B) 2  10²¹

C) 2  10²³

D) 2  10²⁵

Section: 17-1

2. What type of galaxy has a nuclear region of more or less uniform brightness from which long lanes of stars curve outward?

A) spiral

B) quasar

C) irregular

D) elliptical

3. What is the basic shape of a spiral galaxy?

A) round, flat disk with long lanes of stars that curve outward from a round, nuclear region bulging out of the disk

B) round, flat disk with long lanes of stars that curve outward from the center of the galaxy

C) approximately spherical with long lanes of dark dust clouds curving through it in a spiral pattern

D) round, thin disk of uniform brightness with its edges bent up and down into a spiral shape

4. In spiral galaxies, the tightness of the winding of the spiral arms appears to be related directly to the

A) age of the galaxy, as determined from the age of its individual stars.

B) number of globular clusters in the halo of the galaxy.

C) overall intrinsic size of the galaxy, or the diameter across the spiral arms.

D) size of the central bulge of the galaxy.

5. In a spiral galaxy, the

A) spiral arm tightness is independent of the size of the nuclear bulge; a particular bulge can have a wide range of spiral structure.

B) smaller the nuclear bulge is, the tighter the spiral.

C) tighter the spiral is, the larger the nuclear bulge.

D) larger the nuclear bulge is, the looser the spiral.

6. What is the classification for a spiral galaxy with a large nuclear region and tightly wound arms?

A) Sb

B) SBc

C) Sc

D) Sa

7. What is the classification for a spiral galaxy with a moderately sized nuclear region and moderately wound arms?

A) Sc

B) SBc

C) Sa

D) Sb

8. According to the Hubble classification scheme, an Sc galaxy has a(n)

A) round or spherical appearance with a smooth light distribution.

B) large central bulge and tightly wound spiral arms.

C) irregular shape with no obvious disk or spiral arms.

D) small central bulge and loosely wound spiral arms.

9. What is the classification for a spiral galaxy with a small nuclear region and loosely wound arms?

A) Sa

B) Sc

C) SBa

D) Sb

10. A spiral galaxy is observed edge-on so that its spiral arms are barely visible. The galaxy, however, is observed to have a very large nuclear bulge. Thus, this galaxy

A) is probably type Sa.

B) is probably type Sb.

C) is probably type Sc.

D) cannot be classified if its spiral arms cannot be studied.

11. According to the Hubble classification scheme, an Sa galaxy has

A) a large central bulge and tightly wound spiral arms.

B) an irregular shape with no obvious disk or spiral arms.

C) a round or spherical appearance with a smooth light distribution.

D) a small central bulge and loosely wound spiral arms.

12. A spiral galaxy is observed edge-on so that the spiral arms cannot be seen clearly. Is it possible to classify this into one of the Sa, Sb, and Sc categories?

A) Yes. The classification scheme is also an evolutionary scheme. It is possible to classify galaxies by age, for example, by counting the number of blue supergiants visible along the edge.

B) Yes. The tightness of spiral arms is correlated with the size of the nuclear bulge.

C) Yes. The tightness of spiral arms is correlated with the number of bright H II regions that can be counted along the edge.

D) No. The classification scheme is based on the tightness of spiral arms. If the arms cannot be seen, the galaxy cannot be classified.

13. A spiral galaxy has well-defined arms that are wound not-too-tightly around its intermediate-size bulge. This is MOST likely a

A) flocculent Sa.

B) grand-design Sb.

C) flocculent Sb.

D) grand-design Sc.

14. The Andromeda Galaxy (M31) is BEST described as a(n)

A) spiral collection of stars, dust, and gas, 200,000 ly across.

B) extension of the Milky Way.

C) vortex surrounding a black hole.

D) gaseous nebula extending for 6° across Earth’s sky.

15. An astronomer studying a distant cluster of galaxies finds that several of the galaxies are spiral-shaped, with a large nuclear region and tightly wound arms. How should the astronomer classify these galaxies?

A) Sb

B) SBb

C) Sa

D) Sc

16. An astronomer studying a distant cluster of galaxies finds that several of the galaxies are spiral-shaped, with a nuclear region of moderate size and moderately wound arms. How should the astronomer classify these galaxies?

A) SBa

B) Sc

C) Sb

D) Sa

17. An astronomer studying a distant cluster of galaxies finds that several of the galaxies are spiral-shaped, with a small nuclear region and loosely wound arms. How should the astronomer classify these galaxies?

A) Sa

B) SBb

C) Sc

D) Sb

18. What does a spiral galaxy look like when seen edge-on?

A) thick, straight line of light with a central light bulge

B) circular, with no evidence of spiral arms since they are hidden by dust and gas

C) thick line curved into a spiral shape

D) thick, straight line with constant thickness

19. Spiral galaxies are classified in terms of increasing tightness of their spiral arms as types Sa, Sb, and Sc. However, many spiral galaxies are aligned edge-on to Earth and their spiral arms cannot be seen. Which other parameter that is directly related to spiral-arm tightness can be easily seen edge-on and can therefore be used to provide this classification?

A) overall spectral color

B) overall intrinsic brightness of the galaxy, or its absolute magnitude

C) size of the nuclear bulge

D) overall diameter of the galaxy

20. A particular galaxy appears round, with a nuclear region of uniform brightness and an outer region that is broken up into curved but fuzzy and poorly defined lanes of stars and light gas clouds. How would this galaxy be classified?

A) elliptical

B) grand-design spiral

C) flocculent spiral

D) irregular

21. A particular galaxy appears round, with a nuclear region of uniform brightness and an outer region that is broken up into long, curved, well-defined lanes of stars and light gas clouds. How would this galaxy be classified?

A) elliptical

B) flocculent spiral

C) irregular

D) grand-design spiral

Section: 17-2

22. One difficulty with the density wave theory is that

A) the theory fails to explain why a given spiral pattern lasts only a small fraction of the lifetime of a galaxy.

B) the theory fails to provide a mechanism for star formation.

C) astronomers are unsure of the mechanism that produces the energy output necessary to sustain the density wave.

D) the theory fails to explain the distribution of Population I and Population II stars in the galaxy.

23. According to the theory of self-propagating star formation, the spiral arms of flocculent spiral galaxies are broad and poorly designed because

A) the spiral arms in these galaxies are strongly influenced by the black hole at the center of the galaxy.

B) the density wave has been disrupted by the bar across the center of the galaxy.

C) dust lanes occur in broad bands rather than in the narrow bands found in grand-design spirals.

D) the spiral arm segments are defined only by the relatively short-lived O- and B-type stars.

24. In the self-propagating star formation theory

A) spiral arms are formed and sustained primarily by the actions of solar-mass stars because there are so many more of them than there are high-mass stars.

B) spiral arms are poorly defined because they are formed and sustained primarily by the actions of short-lived massive stars.

C) the passage of dust clouds through the spiral arms triggers star formation.

D) spiral structure results with thin, well-defined arms.

25. Self-propagating star formation requires many mechanisms to spread star formation over a region. Which of these is NOT one of them?

A) the influence of black holes

B) winds from newly formed stars

C) shock waves from supernovae

D) radiation from newly formed stars

26. What mechanism is believed to produce flocculent spiral galaxies?

A) satellite galaxies plunging through the disk of the nuclear spiral galaxy

B) self-propagating star formation, where star formation occurs in bursts

C) shock waves from explosive star formation in the nuclear bulge

D) density waves in the interstellar medium

27. How does the winding dilemma affect flocculent spirals?

A) The winding dilemma is the basic cause of the chaotic structure in flocculent spirals.

B) The winding dilemma affects only galaxies with flat rotation curves and constant stellar speeds, and this does not include flocculent spirals.

C) Flocculent spirals are dominated by self-propagating star formation in which groups of stars are formed and then fade as the massive luminous stars complete their life cycles. This transient, spotty star-formation pattern is unaffected by the winding dilemma.

D) Flocculent spirals have a whirlpool structure with several centers of rotation, each affected by the winding dilemma. This results in the overall flocculent pattern.

28. What mechanism is believed to produce grand-design spiral galaxies?

A) shock waves from explosive star formation in the nuclear bulge

B) density waves in the interstellar medium

C) satellite galaxies plunging through the disk of the nuclear spiral galaxy

D) self-propagating star formation, where star formation occurs in bursts

29. Spiral density waves move through a medium that is also moving. The speed of the density waves

A) is greater than the speed of the medium through which they pass.

B) is the same as that of the medium through which they pass, thus forming a rigid spiral pattern.

C) is less than that of the medium through which they pass.

D) varies as the waves go around the galaxy, slowing down while passing through a spiral arm and speeding up in the regions in between.

30. Why do the spiral arms show up so clearly in spiral galaxies?

A) Stars are spread almost uniformly over the galaxy (outside the nuclear bulge), but the brightest stars occur only in the spiral arms, where their brightness and the fact that they illuminate gas clouds make the arms stand out.

B) Stars are spread uniformly over the galaxy, but the dust forms a spiral pattern, absorbing starlight; the spiral arms are the dust-free regions between the dust lanes.

C) The number of stars in the arms is several times larger than in the regions between, so these arms are reasonably distinct.

D) Stars occur only in the spiral arms (and the nuclear bulge), with essentially none between the arms, so the arms show up very distinctly.

31. Which one of these statements about the spiral arms of grand-design spirals is true?

A) The density of matter in the spiral arms is many times the density of the regions in between.

B) The regions between the spiral arms are cloaked in dust, which makes them look dimmer than the spiral arms.

C) The spiral density waves, which move around the galaxy, are transverse waves, moving up and down across the direction of the waves motion like light waves.

D) The spiral arms have almost the same density as the rest of the disk. They are more visible because they contain bright, newly formed stars.

32. Grand-design spiral galaxies

A) have a central bulge that does not rotate.

B) are encompassed within a large lens-shaped disk of dark matter.

C) are orbited by globular clusters that also exhibit star formation.

D) are most often near a companion galaxy.

33. Why is it surprising to find spiral arms in spiral galaxies?

A) Spiral arms require new stars, and previous new stars should have already used up the interstellar medium; no new stars should be forming now.

B) The variations in speed of the stars across galaxies are not high enough to twist the shape of the arms into a spiral.

C) There is no known mechanism to generate spiral arms.

D) The motions of the stars and differential rotation of the galaxy should have wound their arms tightly and made them blend and disappear.

34. Which of these accurately characterizes an apparent dilemma in understanding the spiral arm structure of a typical spiral galaxy?

A) The measured speeds of stars in the galaxy are exactly correct for the present spiral structure, having spun the observed tightness of the spiral in the typical lifetime of a galaxy.

B) If the measured speeds of stars in the galaxy had spun the arms into shape, these arms would be far less tightly wound than the observed arms.

C) If the measured speeds of stars in the galaxy had spun the arms into shape, these arms would be far more tightly wound than the observed arms.

D) The measured speeds of material in the spiral arms should not have led to any spiral but should have generated a straight bar rotating like a solid object.

35. In which of these ways is the Milky Way Galaxy different from most spiral galaxies?

A) The Milky Way has only three spiral arms, whereas most spiral galaxies have at least four.

B) The Milky Way has only two spiral arms, whereas most galaxies have at least four.

C) The spiral arms of the Milky Way are far more tightly wound than those in most galaxies.

D) The Milky Way has at least four spiral arms, whereas most spiral galaxies have only two.

36. How does the amount of dust and gas in a spiral galaxy vary with the classification of the galaxy?

A) The most loosely wound galaxy, Sc, has the most dust and gas in its arms.

B) All spiral galaxies Sa, Sb, and Sc types have about the same fraction of gas and dust within them, about 4% by mass.

C) Only the most tightly wound spiral galaxies, type Sa, have any dust or gas in them at all.

D) The most loosely wound galaxy, Sc, has the least dust and gas in its arms.

37. What is a probable mechanism for the initial triggering, and the subsequent maintenance, of the density wave that forms the visible arms in spiral galaxies?

A) equivalent of a massive “sound” wave generated at the center of the galaxy by the gravitational energy release at the initial formation of the galaxy, producing progressive compression of material that is shaped by galaxy rotation

B) gravitational influence from the rotating central supermassive black hole at the galactic center of the arm material

C) gravitational interaction from the close passage of another galaxy

D) shock waves from supernova explosions of massive stars within the spiral arms

38. How many stars per cubic parsec are there in the spiral arms of a spiral galaxy compared with the regions between the spiral arms?

A) The density of stars inside spiral arms is more than 100 times that in the regions between the arms.

B) The density of stars inside spiral arms is about twice that in the regions between the arms.

C) There are a lot of stars in the spiral arms and none at all in the regions between the arms.

D) The density of stars inside spiral arms is about 5% more than in the regions between the arms.

39. What is the distribution of stars in the spiral arms of a typical spiral galaxy?

A) The density of stars in the arms is far higher than the density of stars between the arms.

B) Far fewer but brighter stars exist in the arms, while many more fainter stars exist between the arms.

C) All the stars of a spiral galaxy are in the arms; there are none at all between the arms.

D) The density of stars is relatively uniform in the disk of the galaxy but is slightly higher within the arms than between them.

Section: 17-3

40. What is a barred spiral galaxy?

A) galaxy with a bar through the nuclear bulge and the spiral arms starting from the ends of the bar

B) spiral galaxy with a straight bar instead of a nuclear bulge

C) galaxy in which the arms form straight bars instead of curved lines

D) galaxy with a bar extending across the entire diameter and the arms starting at various positions along the bar

41. Barred galaxies

A) are increasing in number as the universe ages.

B) are mostly leading-arm spirals.

C) all have tightly wound spiral arms.

D) all have spiral arms wound with various degrees of tightness.

42. What is the designation given to a galaxy with a large nuclear bulge and tightly wound arms starting from a bar through the nuclear bulge?

A) Sb

B) SBa

C) SBc

D) Sa

43. What is the designation given to a galaxy with a small nuclear bulge and loosely wound arms starting from a bar through the nuclear bulge?

A) SBc

B) SBa

C) Sb

D) Sc

44. What is an SBc galaxy?

A) galaxy with a moderate nuclear bulge, moderately wound arms, and a bright core

B) galaxy with a large nuclear bulge and tightly wound arms starting from the ends of a straight bar through the nuclear bulge

C) galaxy with a small nuclear bulge and loosely wound arms coming from the center of the nuclear bulge

D) galaxy with a small nuclear bulge and loosely wound arms starting from the ends of a straight bar through the nuclear bulge

45. A grand-design spiral of type SBa has all of these EXCEPT

A) tightly wound spiral arms.

B) a central bar.

C) about 25% gas and dust.

D) a halo of globular clusters.

46. What is the MOST widely accepted Hubble classification of the Milky Way Galaxy?

A) Sab

B) SBa

C) SBab

D) Because of the difficulty of examining the structure of the Milky Way from inside, the Galaxy has not been classified.

47. How many barred spiral galaxies are there compared with ordinary spiral galaxies?

A) There are about half as many barred spirals as there are ordinary spirals.

B) There are about twice as many barred spirals as there are ordinary spirals.

C) About 1 in 10 spiral galaxies contains a bar.

D) The numbers are essentially equal.

48. How does the number of barred spiral galaxies in the universe compare with the number of ordinary spiral galaxies?

A) Barred spirals outnumber ordinary spirals.

B) There are about equal numbers of barred spirals and ordinary spirals.

C) The question is meaningless—barred spirals are simply ordinary spirals seen edge-on.

D) Ordinary spirals outnumber barred spirals.

49. What happens in the bar of a barred spiral?

A) The bar rotates like a rigid body with no relative motion of the stars and gas inside.

B) The bar is part of the spiral arm structure, and it is actually a shock wave moving through the relatively rapid circular motion of the individual stars.

C) Stars tend to enter one end of the bar, pass through the bar, and exit the other end.

D) Stars and gas tend to move along highly elliptical orbits within the bars.

50. How do nearly all spiral galaxies rotate?

A) The arms lead as the galaxy rotates (the arms point forward).

B) Spiral galaxies do not rotate; if they did, the spiral pattern would soon disappear.

C) Astronomers do not know; spiral galaxies rotate far too slowly for them to have seen any motion in the time since galaxies were discovered.

D) The arms trail as the galaxy rotates (the arms point backward).

51. Doppler measurements of the motions of stars in nearby spiral and barred galaxies indicate that

A) in most spiral and barred galaxies, the arms trail behind the rotating nucleus.

B) in most spiral and barred galaxies, the arms rotate ahead of the nucleus; that is, spiral and barred galaxies are mostly leading-arm galaxies.

C) in most spiral and barred galaxies, the arms lead the rotation of the nucleus; that is, the arms spin faster than the nucleus.

D) about half of all galaxies have trailing arms—the stars rotate slower than the nucleus—while in the other half, the arms rotate ahead of the nucleus.

52. What is a lenticular (or S0) galaxy?

A) galaxy with a central bulge and a disk like a spiral galaxy but with no spiral arms

B) galaxy with a smooth brightness profile and lacking the central bulge and disk of a spiral galaxy

C) galaxy with a lot of gas and dust and no particular structure

D) spiral galaxy with fuzzy and poorly formed spiral arms

53. The Hubble classification description for an S0 galaxy is a

A) small central bulge with loosely wound spiral arms.

B) disk and central bulge with a smooth light distribution and no spiral arms.

C) large central bulge with tightly wound spiral arms.

D) round or spherical shape with a smooth light distribution and no disk or central bulge.

54. An astronomer studying a cluster of galaxies finds a galaxy that is round and has a disk and central bulge like a spiral galaxy but has no spiral arms. How should the astronomer classify this galaxy?

A) E0

B) E7

C) Sa

D) S0

Section: 17-4

55. What is an elliptical galaxy?

A) galaxy with an elliptical outline and a smooth distribution of brightness but no apparent structure

B) spiral galaxy seen from an angle, giving it an elliptical profile

C) galaxy with an elliptical halo when observed at radio wavelengths

D) spiral galaxy with an elliptically shaped nuclear bulge and the spiral arms starting from the ends of the ellipse

56. Elliptical galaxies look far less impressive than spiral galaxies because

A) they contain far fewer stars.

B) there are none within this Local Group, so the only elliptical galaxies seen are at very large distances from Earth.

C) they contain no gas and dust clouds or young, hot stars.

D) they are always smaller.

57. Arrange these objects according to size, largest to smallest.

A) globular clusters, traditional dwarf elliptical, ultra-compact dwarfs

B) globular clusters, ultra-compact dwarfs, traditional dwarf elliptical

C) traditional dwarf elliptical, ultra-compact dwarfs, globular clusters

D) ultra-compact dwarfs, traditional dwarf galaxies, globular clusters

58. Arrange these objects in order of increasing size.

A) ultra-compact dwarfs, globular clusters, spiral galaxies

B) globular clusters, ultra-compact dwarfs, spiral galaxies

C) globular clusters, spiral galaxies, ultra-compact dwarfs

D) ultra-compact dwarfs, spiral galaxies, globular clusters

59. What name is given to a galaxy with a smooth distribution of brightness and a round shape?

A) SBa

B) Sa

C) E7

D) E0

60. What name is given to a galaxy with a smooth distribution of brightness and a very elongated shape?

A) Sc

B) SBc

C) E0

D) E7

61. What is an E3 galaxy?

A) galaxy with a smooth light distribution and a moderately elongated elliptical shape without a disk or central bulge

B) galaxy with a smooth light distribution and a very elongated elliptical shape without a disk or central bulge

C) galaxy with a smooth light distribution and a moderately elliptical shape, having a pronounced disk and central bulge

D) galaxy with an irregular light distribution and a very elongated shape

62. According to the Hubble classification scheme, an E4 galaxy has a(n)

A) disk and central bulge with a smooth light distribution and no spiral arms.

B) irregular shape.

C) round or spherical shape with a smooth light distribution and no disk or central bulge.

D) moderately elliptical shape (a flattened circle) with a smooth light distribution.

63. Lenticular galaxies, S0, have no spiral arms. What is the difference between an S0 and an elliptical E0, which also has no spiral arms?

A) There is no difference. These are two different designations for the same thing.

B) An S0 will have more gas and dust than an E0.

C) The S0 will contain primarily Population II stars while the E0 has primarily Population I stars.

D) The S0 will be likely to contain supernova remnants while ellipticals never contain supernova remnants.

64. According to the Hubble classification scheme, an E3 galaxy

A) is rounder-looking than an E5 galaxy.

B) has more tightly wound spiral arms than an E5 galaxy.

C) is more elongated than an E5 galaxy.

D) has a shorter central bar in its disk than an E5 galaxy.

65. According to the Hubble classification scheme, an E6 galaxy

A) has more tightly wound spiral arms than an E2 galaxy.

B) has a shorter central bar in its disk than an E2 galaxy.

C) is rounder-looking than an E2 galaxy.

D) is more elongated than an E2 galaxy.

66. Which one of these statements does NOT correctly describe typical elliptical galaxies?

A) Typical elliptical galaxies have a central bulge and a disk but no spiral arms.

B) Typical elliptical galaxies have a smooth light distribution with various degrees of elongation from a circular shape.

C) Typical elliptical galaxies contain primarily low-mass stars.

D) Typical elliptical galaxies cover the entire range of masses from the smallest to the largest galaxies in the universe.

67. Which one of these statements is NOT a characteristic of elliptical galaxies?

A) Elliptical galaxies are almost devoid of interstellar gas and dust.

B) Almost all star formation stopped in elliptical galaxies billions of years ago.

C) Different elliptical galaxies appear to be flattened by different amounts.

D) Elliptical galaxies have a disk and a central bulge but no spiral arms.

68. Which one of these properties is NOT typical of elliptical galaxies?

A) old Population II stars

B) old supernova remnants

C) neutron stars

D) dark nebulae

69. In which category of galaxy do astronomers find the largest galaxies in the universe?

A) lenticular galaxies

B) large spiral galaxies like the Milky Way

C) irregular galaxies

D) elliptical galaxies

70. At visible wavelengths, which galaxies are the brightest in the universe?

A) giant elliptical galaxies

B) lenticular galaxies

C) large spiral galaxies like the Milky Way

D) starburst galaxies

71. Compared to the Milky Way Galaxy, a giant elliptical like M86 has

A) more gas and dust.

B) a higher rate of star formation.

C) more stars.

D) spiral arms that are more loosely wound.

72. The biggest and intrinsically brightest galaxies in the universe are members of which group?

A) irregular galaxies

B) barred spirals

C) large spirals

D) ellipticals

73. The largest range of sizes of galaxies is found in which class of galaxies?

A) spiral galaxies

B) irregular galaxies

C) elliptical galaxies

D) starburst galaxies

74. Which class of galaxies has the greatest range of sizes in the universe?

A) irregular galaxies

B) ellipticals

C) lenticular galaxies

D) spirals

75. Which of these types of galaxies contains primarily Population II, metal-poor, low-mass, long-lived stars?

A) elliptical galaxies

B) barred spiral galaxies

C) starburst galaxies

D) flocculent spiral galaxies

76. An elliptical galaxy typically contains which of these kinds of stars?

A) primarily young, metal-rich stars

B) stars of all ages, but all metal-poor

C) primarily old, metal-poor stars

D) stars of all ages from young, metal-rich stars to old, metal-poor stars

77. An astronomer studying a galaxy finds that its spectrum shows only old, low-mass, Population II stars, and photographs of the galaxy show little or no interstellar gas or dust. What kind of galaxy is this astronomer studying?

A) elliptical galaxy

B) spiral galaxy

C) barred spiral galaxy

D) irregular galaxy

78. Which of these galaxy types contain little or no interstellar dust or gas?

A) ellipticals

B) barred spirals

C) irregulars

D) spirals

79. In which of these types of galaxies is star formation no longer occurring?

A) irregular galaxies

B) barred spiral galaxies

C) spiral galaxies

D) elliptical galaxies

Section: 17-5

80. How are the Magellanic Clouds, the two nearby satellite galaxies of the Milky Way Galaxy, classified?

A) elliptical galaxies

B) irregular galaxies

C) flocculent spiral galaxies

D) grand-design spiral galaxies

81. The Magellanic Clouds as seen from the southern hemisphere are examples of what type of objects?

A) irregular galaxies

B) supernova remnants

C) planetary nebulae

D) spiral galaxies

82. What are the Magellanic Clouds?

A) Type I irregular galaxies near the Milky Way Galaxy

B) Type II irregular galaxies near the Milky Way Galaxy

C) globular clusters in the halo of the Milky Way Galaxy

D) very large clouds of gas and dust that are part of the outer halo of the Milky Way Galaxy

83. What is an ultra-diffuse galaxy?

A) a giant elliptical galaxy

B) a disk galaxy with no apparent spiral structure

C) a dwarf elliptical

D) a massive galaxy emitting only 1% as much light as the Milky Way

Section: 17-6

84. Who developed the classification system that divides galaxies into spiral, elliptical, and irregular and classifies spirals by the size of their nuclear region and the tightness of the winding of their arms?

A) Ejnar Hertzsprung

B) Edwin Hubble

C) Sir John Herschel

D) Olaus Roemer

85. Which of these terms does NOT name one of the four main categories of galaxies in the Hubble classification scheme?

A) normal spirals

B) barred spirals

C) starbursts

D) ellipticals

86. Who developed the tuning-fork diagram connecting the different shapes of elliptical and spiral galaxies?

A) Stephen Hawking

B) Ejnar Hertzsprung

C) Martin Schwarzschild

D) Edwin Hubble

87. How do galaxies evolve on the Hubble tuning-fork classification scheme and what is the evolutionary significance of this diagram, shown in Figure 17-15 of the text?

A) About three-quarters of galaxies do not evolve, but others can change their position. Usually, spiral galaxies merge to form ellipticals.

B) The “young” irregular and lenticular galaxies in the center of the tuning fork evolve to either elliptical galaxies if the material is metal-poor or spiral galaxies if the material is metal-rich.

C) Stars slowly die and the spiral arms slowly spin up and tighten to transform spiral galaxies into elliptical galaxies.

D) Elliptical galaxies slowly condense and spin up to form spiral galaxies, the increasing stellar collisions forming the interstellar material in the spiral arms.

88. Which of these statements describes a way in which galaxies evolve on the Hubble tuning-fork diagram?

A) Galaxies begin as type E0 and evolve to lenticular and then continue as either normal or barred spirals.

B) Galaxies are created as either normal or barred spirals, but either eventually evolves to lenticular. These then evolve through the various types of ellipticals.

C) Everything starts as a lenticular galaxy. Then, for reasons not well understood, the subsequent evolution is either as a spiral (normal or barred) or as an elliptical.

D) Spiral galaxies merge to form giant elliptical galaxies.

89. On the Hubble tuning-fork diagram shown in Figure 17-15 of the text, the irregular galaxies are placed between the tines at the right end of the diagram. Why is this?

A) These are the least-massive galaxies, and on the diagram the masses increase from left to right.

B) These are the youngest galaxies, and on the diagram the ages increase from right to left.

C) These are the oldest galaxies, and on the diagram the ages increase from left to right.

D) The placement is somewhat arbitrary.

90. A typical spiral galaxy has _____ stars in a disk of diameter _____ ly.

A) 10¹¹; 10⁵

B) 10¹¹; 1000

C) 10⁹; 10⁶

D) 10⁶; 10⁵

91. The typical diameter of a spiral galaxy is about

A) 10⁷ ly.

B) 10⁵ ly.

C) 1 ly.

D) 100 ly.

Section: 17-7

92. When swirling eddies of gas-rich matter in the universe collide and form a disk centered on an especially massive black hole and lots of dark matter, astronomers believe that this type of galaxy will form.

A) normal spiral

B) barred spiral

C) giant elliptical

D) irregular

93. Did the distribution of dark matter affect the initial formation of galaxies?

A) No. The theory of the early formation of galaxies does not involve dark matter.

B) Yes. Spiral galaxies of all types appear to have formed only in the presence of supermassive black holes and abundant dark matter.

C) Yes. The greatest concentrations of dark matter appear to have led to the formation of the earliest giant ellipticals.

D) Yes. When the concentration of dark matter was not particularly large the formation of barred spirals resulted.

Section: 17-8

94. Overall, through space, galaxies are

A) distributed uniformly, out to the farthest distances.

B) clustered together in several high-density centers with very little matter linking them together.

C) concentrated around one position in space, presumably the original site of the Big Bang.

D) concentrated on filaments separated by huge open spaces or voids.

95. How are galaxies spread throughout the universe?

A) Galaxies are densest near the Milky Way Galaxy and become less and less numerous the farther one looks out into the universe.

B) Galaxies are grouped in clusters that are spread more or less evenly throughout the universe.

C) Galaxies are spread more or less evenly throughout the universe.

D) Clusters of galaxies exist that are themselves often clustered into superclusters. Clusters and superclusters appear to be distributed around giant empty voids.

96. A supercluster of galaxies is a

A) cluster of galaxy clusters.

B) cluster of galaxies that is packed much more densely than normal clusters, giving it a higher mass.

C) phrase describing all the galaxies in the universe as a single system.

D) cluster of galaxies that is spread out over a larger than normal volume of space.

97. How are superclusters spread throughout the universe?

A) Superclusters are distributed more or less evenly (i.e., at random) throughout the universe.

B) Superclusters are distributed in long lines that cover the universe like a gigantic fishing net.

C) Superclusters are separated by large voids, appearing at the intersection of filaments.

D) Superclusters are grouped into clusters of superclusters that in turn are grouped into clusters of clusters, and so on.

98. Which of these are NOT typically gravitationally bound?

A) open star clusters and superclusters of galaxies

B) globular clusters and superclusters of galaxies

C) galaxy clusters and superclusters

D) globular clusters and galaxy clusters

99. Galaxies in the universe are

A) distributed randomly, their density remaining approximately constant throughout space.

B) collected into superclusters that are concentrated along filaments surrounding empty spaces that contain very few galaxies.

C) concentrated into a central supercluster with other clusters rotating about it in a huge, flat disk like a supergalaxy, with very few galaxies outside this disk.

D) all concentrated in spherical clusters, and these clusters are distributed uniformly throughout space.

100. In discussing galaxies and the universe, astronomers often talk about “voids.” What are voids?

A) large expanses of space between galaxies where there is essentially no gas or dust

B) holes in some galaxies where a collision by another, smaller galaxy has removed the dust, gas, and stars in that region

C) volumes of space hundreds of millions of light-years across that contain almost no galaxies

D) regions in clusters of galaxies that seem to be devoid of matter

101. Galaxies throughout the universe appear to be distributed

A) mostly in a single spherical shell surrounding a void in space presumed to have been caused by a vast explosion at the time of the Big Bang.

B) around a single point in space, the presumed location of the original Big Bang that created the universe.

C) in groups and filaments surrounding vast voids.

D) uniformly throughout space.

102. The relationship between a galaxy and the galaxy cluster of which it is a part is similar to the relationship between a galaxy cluster and the supercluster of which it is a part, with one important difference. What is that difference?

A) Clusters contain only like galaxies (spirals, etc.); superclusters combine clusters of various types.

B) Superclusters rely on copious amounts of dark matter to bind them together; clusters do not.

C) A cluster is a gravitationally bound system; a supercluster is not.

D) The galaxy clusters in a supercluster orbit an enormous black hole; this is not the case with the galaxies in a cluster.

103. In which of these cases does gravity, a long-range force, NOT result in a bound system?

A) orbital movements of globular clusters about the center of the Milky Way

B) disruption by tidal forces from the Milky Way of the most recently discovered member of the Local Group, Canis Major Dwarf, a close companion of the Milky Way Galaxy

C) motions of galaxies within clusters

D) motions of clusters within superclusters

Section: 17-9

104. The Milky Way Galaxy is a(n)

A) member of a poor cluster of galaxies.

B) member of a rich, irregular cluster of thousands of galaxies.

C) isolated galaxy, not a member of any cluster.

D) member of a rich, regular cluster of thousands of galaxies.

105. What is the Local Group?

A) stars that occupy the same spiral arm as the Sun

B) poor cluster of about 50 galaxies of which the Milky Way is one

C) group of galaxies clustered around the Andromeda Galaxy M31, apparently gravitationally bound to it but separate from the Milky Way

D) group of about 100 stars within 20 ly of the Sun that appear to have been formed at about the same time from similar material

106. The Local Group is

A) the name of the spiral arm of the Milky Way Galaxy in which the Sun is located.

B) a poor cluster of galaxies in which the Milky Way is located.

C) the family of planets around the Sun.

D) a star cluster to which the Sun belongs.

107. Which of these bodies is NOT one of the satellite galaxies that surround the Milky Way Galaxy?

A) Small Magellanic Cloud

B) Large Magellanic Cloud

C) Andromeda Galaxy

D) Canis Major Dwarf elliptical galaxy

108. Which of these characteristics does the Local Group of galaxies NOT have?

A) poor cluster

B) irregular cluster

C) domination by a central giant elliptical

D) several large spirals

109. What is a rich cluster of galaxies?

A) cluster with more spiral galaxies than ellipticals

B) cluster (like the Local Group) that contains at least two large galaxies

C) cluster with a high metal content

D) cluster containing thousands of galaxies

110. What is a poor cluster of galaxies?

A) cluster with very few spiral galaxies compared with other types

B) cluster with very little gas or dust

C) cluster with a low metal content

D) cluster containing fewer than 1000 galaxies

111. A spherical cluster of several hundred galaxies is found to contain far more ellipticals than spirals and irregulars. How would one classify this cluster?

A) poor regular

B) poor irregular

C) rich regular

D) rich irregular

112. Clusters of galaxies can be rich or poor, regular or irregular. But one thing they all have in common is that, if all galaxies could be detected, the majority of galaxies would be

A) normal spirals.

B) ellipticals.

C) irregulars.

D) barred spirals.

113. What is the famous Virgo cluster of galaxies?

A) rich, irregular cluster of over 1000 galaxies

B) cluster of unknown type centered on a quasar near the edge of the visible universe

C) rich, regular cluster of thousands of galaxies

D) nearest cluster beyond the Local Group containing about three dozen galaxies

114. Why is the Coma cluster of galaxies a favorite among astronomers?

A) The Coma cluster is the cluster in which the Milky Way Galaxy is situated.

B) The Coma cluster contains two quasars.

C) The Coma cluster is the rich, regular cluster nearest Earth.

D) The Coma cluster is the rich, irregular cluster nearest Earth.

115. The estimated distance from Earth to the Coma cluster of galaxies is about

A) 300 million ly.

B) 200 billion ly.

C) 2 million ly.

D) 10 ly.

116. The light that arrives at Earth from the Coma cluster of galaxies has traveled for approximately how long?

A) 300 billion years

B) 300 million years

C) 92 million years

D) 30 million years

117. Suppose astronomers were able to detect radio signals from an intelligent civilization in the Coma cluster of galaxies. If they were to send a message to this civilization, how long would it take to get a reply?

A) 600 million years

B) 150 million years

C) 75 million years

D) 300 million years

118. The total number of galaxies in a rich, regular cluster of galaxies such as the Coma cluster is believed to be

A) between a few thousand and 10,000.

B) over 1 million.

C) about 1000.

D) several dozen.

119. What is the galaxy content of rich, regular clusters like the Coma cluster?

A) more or less even distribution of spirals, ellipticals, irregulars, and S0 galaxies

B) mostly ellipticals and S0 galaxies and relatively few spirals and irregulars

C) entirely elliptical galaxies

D) mostly spirals and irregulars with relatively few ellipticals and S0 galaxies

120. What is the galaxy content of rich, irregular clusters of galaxies such as the Hercules cluster?

A) about the same number of spirals as ellipticals

B) entirely spirals

C) more than one-half spirals, less than one-quarter ellipticals

D) more than one-half ellipticals, less than one-quarter spirals

121. A rich, regular cluster of galaxies differs from a rich, irregular cluster in that

A) its galaxies are distributed in a regular, highly flattened system (like a disk).

B) it contains fewer galaxies than does an irregular cluster.

C) it lacks the giant elliptical galaxies often found in irregular clusters.

D) it has fewer spirals and more ellipticals and S0 galaxies than an irregular cluster.

Section: 17-10

122. What would happen if the Andromeda Galaxy (a spiral about the same size as the Milky Way Galaxy) collided with the Milky Way?

A) The two galaxies would pass through each other, the stars sailing past each other unharmed, and the interstellar gas and dust clouds would collide to produce a burst of star formation.

B) The two galaxies would pass through each other almost unchanged with essentially no interactions at all.

C) The two galaxies would shatter or even explode, essentially destroying their stars and any life-forms that there may have been (including Earth).

D) All the gas and dust clouds and a great many of the stars would collide with each other, stopping both galaxies and creating a galactic merger.

123. Which of these statements about galactic motions and interactions is MOST accurate?

A) Galaxies occasionally collide with one another, particularly galaxies in clusters.

B) Galaxies are so closely packed in the universe that they are always interacting with one another.

C) The universe is composed of one giant galaxy of which all observed stars are members; thus the question of interaction between galaxies is irrelevant.

D) Galaxies are so widely separated that they never interact or collide.

124. Collisions between galaxies

A) occur only very occasionally to produce spectacular supergalaxies containing many new stars. Only one or two examples have been detected so far.

B) are occurring all the time, all elliptical galaxies having resulted from such collisions. The collisions have cleared out all the gas and dust from these galaxies.

C) never happen since galaxies are so far apart in this universe.

D) can and do occur relatively frequently over cosmological times.

125. Collisions between galaxies

A) do not occur because the distances between galaxies are so vast.

B) are relatively fleeting because galaxies move so rapidly and thus last only a few million years.

C) can last hundreds of millions of years.

D) have little long-term effect on the galaxies involved because gravity is a relatively weak force and the distances over which it must act between galaxies are so great.

126. What is a starburst galaxy?

A) galaxy with streams of stars arching out from one place as if from an explosion

B) galaxy with an unusually large number of red giant stars

C) galaxy that is still in the process of formation from the intergalactic medium and undergoing its first star formation

D) galaxy with an unusually large number of newborn stars

127. What is believed to be the origin of starburst galaxies?

A) Starburst galaxies are slower rotators than other galaxies, so the slower-speed collisions between interstellar clouds produce more star formation.

B) Starburst galaxies are newly formed and are undergoing their initial, rapid star formation.

C) A recent collision with another galaxy has triggered a wave of star formation.

D) A recent series of supernovae has compressed the interstellar medium and started a wave of star formation.

128. A starburst galaxy appears to be a galaxy in which

A) a collision with another galaxy has produced a burst of star formation.

B) most of the energy from the galaxy is being produced by supernovae.

C) a central, supermassive black hole is throwing jets of gas and stars out of the nucleus into intergalactic space.

D) essentially all the star formation took place in a single, billion-year-long burst early in the life of the galaxy.

129. One of the consequences of the collision of two galaxies appears to be

A) a burst of vigorous star birth.

B) a very large explosion, similar to but much larger than a supernova, often known as a superdupernova.

C) almost nothing since stars are widely separated in each galaxy and the probability of star-star collisions is very small.

D) the disappearance of one of them into the central black hole of the other.

130. A close encounter between two galaxies is LEAST likely to trigger starburst in which type of galaxy?

A) ellipticals

B) barred spirals

C) normal spirals

D) irregulars

131. If an astronomer is trying to locate starburst galaxies, which of these would be a good spectral region in which to observe?

A) infrared

B) ultraviolet

C) X-ray

D) gamma ray

132. Which of these phenomena is NOT produced by collisions between galaxies?

A) hot interstellar gas, detected by recent space-borne X-ray telescopes

B) concentration of galaxies into clusters and superclusters

C) distorted spiral arms in many galaxies

D) initiation of significant new star formation in so-called starburst galaxies

133. Which of these is NOT a possible consequence of the interaction of two or more galaxies?

A) Change of galaxy type. For example, two disk galaxies might merge to form an elliptical.

B) Globular clusters can form.

C) The black holes in one or more galaxies dissipate and enhance the intergalactic medium.

D) Gas can be liberated from the galaxies into the intergalactic medium.

134. What is believed to be the origin of giant elliptical galaxies?

A) Giant elliptical galaxies formed as such and have remained unchanged ever since.

B) Giant elliptical galaxies grew by devouring smaller galaxies.

C) Collisions of galaxies in the cluster produce a smooth distribution of stars through the cluster, which sink to the center of the cluster and form giant galaxies.

D) Giant elliptical galaxies have grown continuously since their formation by accretion of intergalactic gas.

135. The Milky Way Galaxy and the Andromeda Galaxy (M31) will probably collide in about 4 billion years. What is the probable result?

A) Both galaxies will disappear and become part of the intergalactic medium.

B) Most of the stars will dissipate into the intergalactic medium, but a smaller spiral galaxy will remain.

C) A giant elliptical will form.

D) An irregular galaxy will form.

136. The temperature of the hot intergalactic gas that results from the merger of galaxies can range from 300,000 to 5 million K. What is the BEST electromagnetic radiation range in which to view this hot gas?

A) X-ray

B) visible

C) infrared

D) radio

137. Starburst galaxies are characterized by an abundance of stars in the process of formation. As a result, these galaxies send out an unusually large amount of electromagnetic radiation in which of these ranges?

A) X-ray

B) visible

C) infrared

D) radio

138. Which one of these occurrences has NOT been observed as evidence of colliding galaxies?

A) very strong X-ray emission coming from rich clusters of galaxies

B) starburst galaxies that contain hot gas, many newborn stars, and relatively young globular clusters

C) streams of hydrogen gas connecting two or more galaxies

D) distribution of black hole candidates throughout a galaxy suggesting many star mergers as a result of a galactic collision

139. What is the dominant radiation from the intergalactic matter in rich clusters of galaxies?

A) ultraviolet light from electrons spiraling in magnetic fields

B) infrared radiation from dust

C) X-rays from very hot gas

D) 21-cm radio radiation from cool, neutral hydrogen gas

140. What is the typical temperature of the intergalactic gas in rich clusters of galaxies?

A) 10,000 to 20,000 K

B) 1 billion to 10 billion K

C) 10 to 100 K

D) 1 million to 100 million K

141. Many rich, regular clusters of galaxies contain substantial amounts of very hot, intergalactic gas. What is believed to have produced this hot gas?

A) collisions between galaxies in the cluster

B) bursts of star formation in merging galaxies

C) supernovae (exploding stars)

D) jets of gas ejected by supermassive black holes at the centers of the galaxies

142. The source of the hot, intergalactic gas in many rich, regular clusters of galaxies appears to be

A) jets of gas ejected by supermassive black holes at the centers of the galaxies.

B) bursts of star formation in merging galaxies.

C) exploding stars or supernovae within individual galaxies.

D) collisions between galaxies in the cluster.

143. Globular clusters

A) are young formations and always contain many hot O- and B-type stars.

B) are old formations and always contain only old, red stars.

C) can be formed in collisions of galaxies and thus can be young if the collision occurred recently.

D) are continually forming in spiral galaxies, like the Milky Way, and thus they show a great range of ages in any one galaxy.

Section: 17-11

144. As much as 90% of the matter in the universe may be unseen “dark matter.” Where is this dark matter in galaxies?

A) Dark matter follows the same distribution as the stars inside galaxies.

B) Dark matter is concentrated in the centers of galaxies and may, in fact, be related to black holes at galactic centers.

C) Dark matter is concentrated in the planes of galaxies but extends far beyond the visible galactic plane.

D) Dark matter appears to be concentrated in spherical halos around galaxies that extend several times the radius of visible matter.

145. Much of the mass in galaxies and clusters of galaxies is dark matter. Which of these techniques is NOT useful for detecting evidence of this dark matter?

A) measuring the speed of stars in their orbits around a galactic center

B) gravitational lensing of very distant galaxies by a nearby galaxy (or cluster) and its accompanying dark matter

C) observing the aftermath of a collision such as that in galaxy cluster 1E0657-56

D) gravitational waves

146. Which single major problem perhaps puzzles astronomers MOST as they attempt to interpret the properties and behavior of clusters of galaxies?

A) rate of supernova occurrence in galaxies in some clusters

B) missing-mass problem, where the amount of mass needed for galactic cluster stability is estimated to be at least 10 times more than the observed visible mass

C) presence of star formation in many galaxies long after it is expected to have died out

D) structure and motion of spiral arms in galaxies in many clusters

147. Which one of these statements about clusters of galaxies is true?

A) The observed mass of the galaxies of the cluster is many thousands of times too small to hold the cluster together.

B) The observed mass of the galaxies of the cluster is about 10 times larger than the amount needed to hold the cluster together.

C) The observed mass of the galaxies in the cluster is about 10 times too small to hold the cluster together.

D) The observed mass of the galaxies of the cluster is almost exactly equal to the mass needed to hold the cluster together.

148. The rotation curve of a galaxy is a graph showing the galaxy’s speed of rotation at different distances from the center. The observed rotation curve in the outer parts of a typical large spiral galaxy

A) is quite flat (roughly the same speed at all distances).

B) decreases suddenly to zero at the outer edge of the visible galaxy.

C) decreases smoothly with increasing distance from the center.

D) increases drastically with increasing distance from the center.

149. If most of the mass of a galaxy is located near the center of the galaxy, then in the outer part of this galaxy the orbital speeds of stars must decrease with increasing distance from the center. This behavior would be equivalent to

A) Newton’s third law.

B) Wien’s law.

C) Hubble’s law.

D) Kepler’s third law.

150. Most of the light from a galaxy comes from the inner parts. If this means that most of the galaxy’s mass is also in the inner region, then how would the galaxy’s speed of rotation behave in its outer region?

A) The rotation speed should increase with increasing distance from the center.

B) The rotation speed should decrease sharply to zero at the outer edge of the visible galaxy.

C) The rotation speed should not change appreciably with increasing distance from the center (i.e., a “flat” rotation curve).

D) The rotation speed should decrease smoothly with increasing distance from the center.

151. Dark, unknown forms of matter appear to make up about what fraction of the mass of a typical rich cluster of galaxies?

A) one-half

B) 90%

C) much less than 1%

D) 10%

152. The mass of the presently observable matter in a typical rich cluster of galaxies appears to be approximately what fraction of the mass required to hold the cluster together by gravity?

A) 10%

B) 100%, or the entire galaxy

C) about 1%

D) 90%

153. Dark matter is matter that gives out no observable radiation and is detected by its gravitational interaction alone. Which of these does NOT provide direct evidence for dark matter?

A) separation of visible and dark matter in collisions of galaxy clusters

B) emission from hot intergalactic gas in galaxy clusters

C) gravitational lensing by unseen objects

D) insufficient visible mass to bind galaxy clusters gravitationally

154. The amount of visible matter in a typical cluster of galaxies is

A) just sufficient to hold the inner regions of the cluster together, but the fringe galaxies are drifting away from this center.

B) not sufficient to hold the cluster together by a factor of 2, such that the cluster is slowly spreading out.

C) insufficient to hold the cluster together, by about a factor of 10.

D) far more than enough to hold the cluster together gravitationally and is slowly concentrating the cluster into a very tight supercluster.

155. One of the big puzzles about the properties and behavior of large clusters of galaxies is that

A) each cluster appears to consist of the same type of galaxy, some made up totally of spiral galaxies while others contain only ellipticals.

B) they appear to be spread uniformly throughout space in all directions, which is difficult to explain with the Big Bang theory.

C) there appears to be insufficient mass in the luminous matter (stars, and so on) to hold the cluster together gravitationally.

D) they appear not to take part in the general expansion of the universe, in contrast to single separate galaxies, probably because they are gravitationally bound to one another.

156. How has the hot, X-ray–emitting intergalactic gas in galaxy clusters affected the dark matter problem for the clusters?

A) The gas supplies the mass needed to solve the problem, which is now no longer a problem!

B) The gas supplies about 10 times too much mass—now the problem is how clusters so massive are not much more compact.

C) The gas supplies about 2/10 of the dark matter, so with the visible matter, about 7/10 of the mass required to stabilize the cluster is still missing.

D) The gas is very tenuous and supplies almost no mass at all; therefore, it has almost no effect on the dark matter problem.

157. One piece of evidence for the existence of dark matter is the

A) absence of interstellar materials (gas and dust) from elliptical galaxies.

B) low count of neutrinos emitted from the center of the Sun.

C) scarcity of dwarf ellipticals in the Local Group of galaxies.

D) discrepancy between observed mass and the required gravitational binding in rich clusters of galaxies.

158. Inside of galaxy clusters, which of these components contains about twice as much mass as the stars inside the cluster’s galaxies?

A) large numbers of cool, dark, brown dwarf stars floating in the galaxy cluster

B) very hot intergalactic gas emitting X-rays in clusters.

C) a tremendous flux of neutrinos, which have recently been shown to have mass, coming from these clusters.

D) large numbers of small but massive black holes within every galaxy.

159. Gravitational lensing of distant objects by closer galaxies indicates that the

A) amount of visible matter in the galaxies accounts for only 10% of the total mass producing the lensing.

B) amount of visible matter in the galaxy is about 10 times too great to account for the observed lensing, leading to the idea of negative gravitation within such large-scale structures.

C) amount of visible matter in the galaxies is sufficient to account for the gravitational lensing.

D) total mass within the galaxies that produces the lensing exceeds the amount of visible matter by a factor of 100.

160. Which of these techniques has NOT provided a means by which astronomers can infer the presence of dark matter in the universe?

A) measurement of the orbital speeds of stars near possible supermassive black holes at the centers of galaxies

B) measurement of the orbital speeds of stars in the outer regions of galaxies

C) observation of the bending of light (gravitational lensing) from remote galaxies as it passes through intervening clusters of galaxies

D) measurement of the line-of-sight speeds of individual galaxies in clusters of galaxies

Section: 17-12

161. Who first discovered that many galaxies are moving away from Earth?

A) Karl Jansky

B) V. M. Slipher

C) Albert Einstein

D) Edwin Hubble

162. Who first showed that the recessional speeds of galaxies increase with increasing distance from Earth?

A) V. M. Slipher

B) Karl Jansky

C) Edwin Hubble

D) Albert Einstein

163. What is the Hubble flow?

A) Distant superclusters of galaxies are all moving toward Earth on one side and away from Earth on the other, as part of a universal flow of galaxies throughout the universe.

B) Distant superclusters of galaxies are all moving away from Earth at approximately the same speed.

C) Distant superclusters of galaxies are all moving away from Earth, their speed increasing with increasing distance.

D) Distant superclusters of galaxies are all moving away from Earth, their speed decreasing with increasing distance.

164. The Hubble law indicates that

A) the Milky Way Galaxy appears to be at or near the center of the known universe.

B) all nearby superclusters of galaxies are moving toward Earth and all faraway superclusters are moving away from Earth.

C) the farther superclusters are receding faster than the nearby superclusters.

D) the universe will expand forever.

165. The primary evidence for the expanding universe concept is the

A) slow spreading out of stars in the near neighborhood of the Sun.

B) redshift of light from distant galaxies, which increases with distance of the galaxy from Earth.

C) discovery of black holes in binary stars.

D) slow increase in the Earth-Moon separation—about 4 cm per year—with time.

166. The Hubble law implies that distances are increasing between

A) the proton and electron in hydrogen.

B) the planets and the Sun.

C) galaxies in the Local Group.

D) superclusters of galaxies.

167. Consider a cluster of galaxies. What is increasing because of the Hubble flow?

A) the average distance between galaxies within the cluster

B) the sizes of the galaxies within the cluster

C) the distance between the cluster and other distant clusters of galaxies

D) the average distance between the stars in each of the cluster galaxies

168. Which two quantities are shown to be related to one another in Hubble’s law?

A) distance and brightness

B) brightness and the width of the 21-cm radio emission line of hydrogen

C) brightness and recession velocity

D) distance and redshift of light from the object

169. The Hubble relation links which two characteristics of distant objects in the universe?

A) distance and recessional velocity

B) luminosity and surface temperature

C) state of organization and the ages of clusters of stars

D) stellar mass and luminosity

170. The Hubble law, representing observations of distant objects in the universe, relates which two parameters?

A) distance to a distant object and the redshift of its light

B) mass of an object and its luminosity

C) luminosity and position of stars in the galaxy

D) mass of a distant object and its recession velocity

171. The Hubble law states that

A) all objects appear to have the same velocity away from the Sun, regardless of distance from the Sun.

B) mutual gravitational attraction of all objects in the universe means that all objects appear to be moving toward the Sun, the closest ones traveling fastest.

C) all distant objects are moving toward the Sun, the most distant objects fastest.

D) the farther an object is from the Sun, the faster it appears to be moving away from the Sun.

172. The Hubble law states that

A) all galaxies are being repelled from the central “engine” of the universe, with the ones closest to the center traveling fastest.

B) all galaxies are being pulled toward a central gravitational attractor in the universe, with the ones closest to the center traveling fastest.

C) the more distant a galaxy is from the Sun, the faster it is traveling toward the Sun.

D) the more distant a galaxy is from the Sun, the faster it is traveling away from the Sun.

173. For which objects in the universe has the Hubble relation been shown to hold experimentally?

A) galaxies in the Local Group, in the near vicinity of the Milky Way

B) stars in the Milky Way in the near neighborhood of the Sun

C) distant galaxies

D) stars in the distant spiral arms of the Milky Way Galaxy

174. Which of these speeds are described by Hubble’s law?

A) speeds of individual galaxies in the Local Group and other nearby galaxy clusters

B) speeds of superclusters of galaxies

C) speeds of stars in the Milky Way Galaxy

D) speeds of individual clusters of galaxies in the Milky Way’s local supercluster

175. The expansion of the universe takes place

A) only over distances about the size of a galaxy or larger; consequently, the Milky Way Galaxy expands, but the solar system does not.

B) only between objects separated by a vacuum; as a result, the bodies do not expand, but the Earth-Moon system does.

C) between all objects, even between the atoms in the bodies, although the expansion of a person is too small to be measured reliably.

D) primarily in the huge voids between clusters of galaxies. “Small” objects like galaxies or Earth do not expand.

176. In this universe, one can consider four different regimes of space in which distances between objects might be changing as a result of the general expansion of the universe: (1) distances between different parts of Earth, (2) distances between planets in the solar system, (3) distances between stars in the Milky Way Galaxy, and (4) distances between superclusters of galaxies. In which of these regimes are the distances changing because of the universal expansion?

A) 4 and 3

B) 4, 3, 2, and 1

C) 4, 3, and 2

D) 4 only

177. The Hubble flow, demonstrating the expansion of the universe, occurs

A) between galaxies in clusters, clusters in superclusters, and superclusters in wider regions of space.

B) only between superclusters of galaxies.

C) between stars in galaxies, galaxies in clusters, clusters in superclusters, and superclusters over wider regions of space.

D) between clusters of galaxies in superclusters and between superclusters over wider ranges of space.

178. Hubble’s law for distant galaxies, with H₀ being Hubble’s constant, states that

A) H₀  recessional speed = distance.

B) recessional speed = H₀  distance.

C) recessional speed = H₀, which is constant.

D) recessional speed  distance = H₀.

179. Which of these expressions is the correct form of Hubble’s law (H₀ = Hubble’s constant, r = distance, v = recessional velocity)?

A) H₀  v = r

B) v = H₀  r

C) v = H₀, which is constant

D) v  r = H₀

180. The mathematical form of the Hubble law for the expanding universe concept relates the velocity of recession v to the distance of the observed object r (with H₀ the Hubble constant) as follows:

A) r = H₀  v

B) v = H₀  r

C) v = H₀/r

D) v = H₀/r²

181. Astronomer A claims that the Hubble constant is 84 km/s per Mpc, while astronomer B claims that it is 63 km/s per Mpc. If, using the Hubble constant, astronomer A claims that a particular galaxy is 4 billion ly away, then astronomer B would claim that it is _____ billion ly away.

A) 3

B) 5.3

C) 6

D) 2

182. Suppose a galaxy is 400 million pc from Earth. What is the recessional velocity of this galaxy? Assume Hubble’s constant to be 73.5 km/s per Mpc.

A) 5 km/s

B) 200,000 km/s

C) 29,400 km/s

D) 5 million km/s

183. An astronomer studying a distant galaxy finds that its recessional velocity is 14,000 km/s. What is the distance to the galaxy? Assume Hubble’s constant to be 73.5 km/s per Mpc.

A) 1,030,000 Mpc

B) 103 Mpc

C) 190 Mpc

D) 1900 Mpc

184. Suppose an astronomer discovers a distant quasar whose recessional velocity is 1/3 the speed of light. If Hubble’s constant is 73.5 km/s per Mpc, how far away is the quasar?

A) 5 million Mpc

B) 145 Mpc

C) 73.5 Mpc

D) 1450 Mpc

185. If the elliptical galaxy in Boötes, shown near the bottom of Figure 17-32 of the text, were at a distance of 1.6 billion ly, what would be the value of Hubble’s constant H₀? (Be careful with units.)

A) about 60 km/s per Mpc

B) about 25 km/s per Mpc

C) about 95 km/s per Mpc

D) about 80 km/s per Mpc

186. In the verification of the Hubble law for the expansion of the universe and the determination of the constant H₀, the greatest difficulty has been

A) allowance for gravitational redshifting of light by high gravitational fields at distant galaxies.

B) accurate determination of distances to very distant galaxies.

C) measurement of recession velocities of distant galaxies by Doppler shift.

D) the identification of distant objects as galaxies, rather than very bright, nearby stars.

187. The method of stellar parallax

A) can be used to measure the distance to stars in distant galaxies just as it can be used for stars in the Milky Way Galaxy.

B) can be used for distant galaxies but only when used with giant molecular clouds (which can be seen at such distances), not with stars.

C) cannot be used for distant galaxies because redshift spectra are inherently imprecise at such distances.

D) cannot be used for distant galaxies because of the difficulty of resolving the spectra of individual stars.

188. What is the present range of measured values of Hubble’s constant from various techniques?

A) somewhere between 200 and 1000 km/s Mpc

B) somewhere between 67 and 75 km/s per Mpc

C) somewhere between 80 and 300 km/s per Mpc

D) between 28 and 32 km/s per Mpc

189. To an astronomer, what is a “standard candle”?

A) standard light source that is placed in a telescope, with which the brightness of stars and other objects can be compared

B) galaxy whose redshift has been measured accurately

C) object whose absolute magnitude or intrinsic brightness is known

D) accurately defined brightness scale for stars and galaxies, such as the magnitude scale

190. Standard candles, which are important for finding distances to remote galaxies, are

A) stars and other objects of known intrinsic brightness.

B) standard laboratory light sources with which the brightness of a galaxy can be compared.

C) standard bars of known length with which the size of a galaxy can be measured.

D) heat sources used for calibrating infrared observations of galaxies.

191. What method is used to determine the distances of very remote galaxies?

A) measurement of the apparent magnitudes of Type Ia supernovae in the galaxies

B) comparison of the apparent and absolute magnitudes of the galaxies

C) measurement of the apparent brightness and period of Cepheid variable stars in the galaxies

D) measurement of the angular size of a galaxy and an assumption about the actual physical size of the galaxy

192. To what distance in parsecs can Cepheid variables now be seen with the Hubble Space Telescope?

A) about 500 Mpc

B) about 50 Mpc

C) about 50 kpc

D) about 5 Mpc

193. What is the brightest standard candle, and therefore the one that is visible to the greatest distance, found so far?

A) Type Ia supernovae

B) brightest H II regions in each galaxy

C) brightest globular cluster of each galaxy

D) Cepheid variables

194. Which of these objects are used as standard candles for distance measurement to distant galaxies?

A) globular clusters

B) hot white dwarf stars

C) supernova explosions

D) elliptical galaxies

195. Which of these observations are NOT used for the measurement of distances to distant galaxies?

A) Cepheid variable stars

B) width of the 21-cm H I radio emission line

C) supernova explosions

D) brightness and pulsation rates of pulsars

196. What is the Tully-Fisher relation?

A) The more distant the galaxy, the greater is the recessional velocity.

B) The brighter the Cepheid, the longer is the pulsation period.

C) The more distant the galaxy, the fainter it appears.

D) The brighter the galaxy, the wider is the 21-cm radio emission line.

197. In the 1970s it was discovered that, among spiral galaxies, the wider the 21-cm radio emission line, the brighter is the galaxy. What is the name of this relation?

A) mass-luminosity law

B) Hawking effect

C) Hubble law

D) Tully-Fisher relation

198. The Tully-Fisher relation provides a method of determining distances to galaxies by estimating the galaxy luminosity from a measurement of which parameter relating to the 21-cm atomic hydrogen radio emission line?

A) width

B) position and hence Doppler shift from the rest wavelength

C) intensity

D) split between its two components

199. The Tully-Fisher relationship relies on broadening of the 21-cm radio line in distant spiral galaxies. What causes this broadening?

A) thermal motion of the gases in the galaxy

B) random motions of the stars in the galaxy

C) rotation of the galaxy

D) general expansion of the universe (Hubble flow)

200. The Tully-Fisher relationship can be used to measure the luminosity of (and thus the distance to)

A) elliptical galaxies.

B) spiral galaxies.

C) globular clusters.

D) Type II supernovae.

201. The distance-measuring techniques, arranged in order of the distance for which they are MOST effective (from least to most) are

A) Cepheid variables, spectroscopic parallax, Type Ia supernovae, and Tully-Fisher relation.

B) spectroscopic parallax, Tully-Fisher relation, Cepheid variables, and Type Ia supernovae.

C) spectroscopic parallax, Cepheid variables, Tully-Fisher relation, and Type Ia supernovae.

D) Cepheid variables, spectroscopic variables, Type Ia supernovae, and Tully-Fisher relation.

202. The width (Doppler broadening) of the 21-cm line in a spiral galaxy is NOT related to which one of these properties of the galaxy?

A) rotation rate

B) mass

C) luminosity

D) age

203. The Tully-Fisher relation can be used to determine the distance to

A) spiral galaxies only.

B) elliptical galaxies only.

C) irregular galaxies only.

D) either spirals or ellipticals.

204. What is astronomers’ present belief about the location of the Milky Way Galaxy?

A) The Milky Way has been shown to be in the center of the universe by the uniformity of the Hubble flow as seen from Earth.

B) The Milky Way has been shown to not be in the center of the universe by the uniformity of the Hubble flow as seen from Earth.

C) The Milky Way has been shown to be in the center of the universe by the distribution of superclusters as seen from Earth.

D) The Milky Way has been shown to not be in the center of the universe by the distribution of superclusters as seen from Earth.

205. Because of the expansion of space, astronomers see all distant galaxies moving away from Earth, with more distant galaxies moving faster. An observer in one of these distant galaxies would see all galaxies

A) moving toward the observer, with more distant galaxies moving faster.

B) moving away from the observer, with closer galaxies moving faster.

C) moving away from the observer, with more distant galaxies moving faster.

D) on one side of the observer moving toward the observer and all galaxies on the other side moving away from the observer, with more distant galaxies moving faster.

Section: 17-13

206. At present, how far away are the MOST distant galaxies astronomers have observed?

A) 970 million ly

B) 6.7 billion ly

C) 13.4 billion ly

D) 56 billion ly

207. By 2016 astronomers were able to observe galaxies about 13.4 billion light-years away. Thus, they were observing these galaxies

A) almost immediately after the Big Bang.

B) a few billion years after the beginning of the universe.

C) at about half their present age.

D) at about 90% of their present age.