2. An atom may become excited by a) colliding with another atom b) absorbing a photon c) both of these d) none of these

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1 Contemporary Astronomy Exam 3 1. Atoms that are isotopes of the same element have a) the same number of protons and neutrons b) different numbers of neutrons c) different numbers of protons d) gained or lost an electron 2. An atom may become excited by a) colliding with another atom b) absorbing a photon c) both of these d) none of these 3. Emission nebulae are red because a. they only occur near red giants b. their light comes from Balmer lines c. they have low temperatures d. they are rich in helium 4. Interstellar gas clouds may collapse to form stars if they a. have very high temperatures b. encounter a shock wave c. are rich in helium 5. Molecular clouds are found a. in areas protected by huge dust clouds b. in all parts of the universe c. only in stars of very high temperatures d. only in the center of galaxies 6. It is possible to detect dust clouds because a. they can be dense enough to block the light of more distant stars and are therefore silhouetted against a background filled with stars b. they can scatter enough starlight of nearby bright stars c. penetrating starlight can be "reddened" relative to the spectral lines it shows d. all of the above 7. Just prior to its arrival on the main-sequence what sort of evolutionary path does a protostar follow on the HR diagram. a. pre-main-sequence stars do not appear on the HR diagram b. approximately horizontal from right to left c. approximately horizontal from left to right d. approximately diagonal from upper left to lower right 8. Protostars are difficult to observe because a. the protostar stage is very short b. they are surrounded by cocoons of gas and dust c. they radiate mainly in the infrared 9. The minimum mass for main-sequence stars is set by a. the minimum mass fragments of star-forming nebulae

2 b. the mass luminosity relation c. the ignition temperature of hydrogen d. the density requirements of the CNO process 10. A star is in a state of balance when gravitational forces and gas pressure are equal. This state is called a. natural balance b. Newtonian equilibrium c. hydrostatic equilibrium d. hydraulic equilibrium 11. Why do stars age? a. all thing age and stars are just following the natural way b. the gravitational collapse of a star must eventually reach its limit c. stars have a finite amount of fuel and it eventually runs out d. the reason stars age is unknown at this time 12. The expected main-sequence lifetime of the Sun is a. about 4.6 billion years b. about 10 billion years c. about 100 billion years d. about 100 million years 13. Given that a solar lifetime is about 10 billion years, a 9 solar mass star will remain on the main sequence for about a. 3 million years b. 27 million years c. 4.6 million years d. 41 million 14. The luminosity of a main-sequence star depends on a. surface area, temperature, and mass b. volume, temperature, and fuel type c. volume, gravity, and temperature d. surface area, gravity, and fuel type 15. In the H-R diagram, 90 percent of all stars fall a) in the giant region b) in the supergiant region c) among the B stars d) on the main sequence 16. The most common stars are a) supergiants b) giants c) upper main-sequence stars and supergiants d) lower main-sequence stars and white dwarfs 17. A star moving away from the earth will have a spectrum containing a) red shifted lines b) blue shifted lines c) unshifted lines d) weaker lines than if approaching earth 18. A star s core must contract as it uses up its hydrogen fuel because

3 a. a central temperature falls b. the number of atoms in the core decreases c. the number of atoms in the core increases d. the density of the core falls 19. When a star exhausts its hydrogen, it a. becomes hotter and brighter b. becomes cooler and brighter c. becomes hotter and fainter d. becomes cooler and fainter 20. Helium fusion is called the triple alpha process because a. the helium nucleus is an alpha particle b. it occurs first c. it precedes the helium flash by 3 percent d. it is the third of the primary energy sources 21. A star first leaves the main sequence when a. the helium flash occurs b. it starts fusing helium via the triple alpha reaction c. its core hydrogen has been depleted d. photodisintegration begins to occur 22. As a 1 solar mass star evolves to the red giant phase a. its surface temperature and luminosity increase b. its surface temperature and luminosity decrease c. its surface temperature increases and its luminosity decreases d. its surfaced temperature decreases and its luminosity increases 23. When a 1 solar mass star begins its move to the red giant stage for the second time it is because a. core hydrogen is depleted b. core helium is depleted c. the helium flash occurs d. a core explosion causes the star's envelope to expand 24. A star will experience a helium flash if a. it is more massive than about 6 solar masses b. its core contains oxygen and helium c. its core is degenerate when helium ignites d. all of the above 25. In degenerate matter a. pressure depends only on temperature b. temperature depends only on density c. pressure does not depend on temperature 26. The transition from a main-sequence star to red giant or supergiant a. takes about the same time for all stars b. takes much longer for stars of greater mass c. takes a little longer for stars of very low mass d. takes much longer for stars of very low mass stars than for high mass stars 27. The Chandrasekhar limit tells us that

4 a. the lowest mass stars cannot become giants b. white dwarfs may not have masses greater than 1.4 solar masses c. giant stars should rotate slower than main sequence stars 28. The Chandrasekhar limit refers to a. the amount of mass that can be supported by degenerate electron gas pressure b. the temperature required for fusion of helium in the core of a star c. the lower limit to the mass of a star that can produce a planetary nebula d. the dividing line between Cepheid and RR Lyrae variable stars 29. A typical white dwarf star a. has a mass close to that of the Sun and a size about half that of the Sun b. has a mass close to that of the Sun and is about the size of the Earth c. has a mass about 1/1000 of the Sun and is about the size of the Earth d. is so small and insignicant that it is very unlikely to ever be seen by astronomers 30. Giant and supergiant stars are rare because a. they do not form as often as main-sequence stars b. the giant and supergiant stage is unstable c. the giant and supergiant stage is very short d. helium is very rare 31. Planetary nebulae are produced when a. a star exhausts its helium and can t ignite carbon b. a star develops an iron core c. a star exceeds the Chandrasekhar limit d. a star becomes degenerate before helium ignites 32. Fusion in the core of a star cannot proceed beyond iron because a. this requires core temperatures that don't exist in the core of stars b. fusion of iron with other iron nuclei or any other nuclei does not release energy c. the Chandrasekhar limit has been reached d. iron is the last element on the periodic table 33. The Schwarzchild radius is a. the radius for a particular mass for which the escape velocity is equal to the speed of light b. the radius that defines the event horizon of a black hole c. the radius at which a particular mass will become a black hole d. all of the above 34. A Type Ia supernovae is produced a. when a high mass star gets to the iron fusion limit b. when a star reaches the Chandrasekhar limit c. as a result of the transfer of fusionable material from a companion star to a white dwarf star whose core is initially just below the Chandrasekhar limit d. as the result of helium flash in a star of 4 to 5 solar masses. 35. A Type II supernovae explosion a. destroys the star b. is triggered by the collapse of an iron core c. can produce a burst of neutrinos

5 36. A pulsar is a. a rapidly spinning active galactic nuclei similar to a quasar b. a rapidly spinning white dwarf star c. a rapidly spinning neutron star d. a rapidly spinning black hole 37. A nova is almost always associated with a. a giant star with a degenerate core b. a white dwarf in a close binary system c. a white dwarf that exceeds 1.4 solar masses d. a star with an iron core 38. The density of a neutron star is a. about the same as that of a white dwarf b. about the same as that of the sun c. about the same as that of an atomic nucleus 39. We expect neutron stars to spin rapidly because a. they conserved angular momentum b. they have high orbital velocities c. they have high densities d. they have high temperatures 40. Although neutron stars are very hot, they are not easy to locate because a. we cannot see inside the event horizon b. most lie beyond dense dust clouds c. solid neutron material cannot radiate photons d. they have small surface areas 41. Pulsars cannot be spinning white dwarfs because a. white dwarfs are not that common b. white dwarfs are not dense enough c. white dwarfs do not have magnetic fields d. a white dwarf spinning that fast would fly apart 42. We believe that pulsars slow down because a. they are converting energy of rotation into radiation b. they are dragging companion stars around c. of friction with the interstellar medium d. of the conservation of angular momentum 43. The event horizon a. is believed to be a singularity b. is a crystaline layer c. has a radius equal to the Schwarzschild radius d. marks the inner boundary of a planetary nebula 44. An isolated black hole in space would be difficult to detect because a. there would be no light source nearby b. it would not be rotating rapidly

6 c. it would be stationary d. very little matter would be falling in 45. We can suspect that Cygnus X-1 and LMC X-3 are black holes if the masses of the unseen companions orbiting them are a. less than 5 solar masses b. more than 5 solar masses c. between 0.4 and 1.4 solar masses d. less than 0.4 solar masses 46. Objects in the galactic halo a. have nearly circular orbits and orbit the center of the galaxy in the same direction as the Sun b. have nearly circular orbits that are randomly oriented c. have elliptical orbits and retrograde orientations d. have elliptical orbits that are randomly oriented. 47. The globular clusters in the spherical component are metal poor because a. they never pass through the disk of the galaxy b. they contain only low mass stars that don t make metals c. they are very old 48. We suspect that our galaxy is surrounded by a galactic corona of dark matter because the disk of the galaxy a. rotates faster than expected in its outer region b. rotates more slowly than expected in its outer region c. rotates faster than expected in its inner region d. rotates more slowly than expected in its inner region 49. Younger stars have more heavy elements because a. old stars destroy heavy elements as they age b. young stars burn their nuclear fuels faster c. heavy atoms were made in previous generations of stars 50. Radio maps of our galaxy show spiral arms because a. the arms have high Doppler shifts b. the gas in the spiral arms is hot enough to emit photons c. the dust is denser in spiral arms d. the gas is denser in spiral arms 51. If the spiral density wave were the only thing producing spiral arms we would expect a. all spiral arms to be dust free b. all galaxies to have grand design spiral patterns c. the Milky Way to be more massive than observed 52. The energy source at the center of our galaxy a. is not visible at optical wavelengths b. produces gamma rays c. must be less than 10 AU in diameter 53. A megaparsec is equivalent to

7 a light-years b. 206,265 light-years c. 206,265 AU d. 3,260,000 light-years 54. Which of the following is not used as a distance indicator? a. Parallax b. large globular clusters c. Type II Supernovae d. Cepheid variable stars 55. If H equals 50 km/sec/mpc, then a galaxy with a radial velocity of 2000 km/sec probably has a distance of a Mpc b Mpc c. 40 Mpc d Mpc 56. Galactic cannibalism refers to a. binary galaxies b. the merging of galaxies c. galaxies drawing in gas from the intergalactic medium 57. We should expect galaxies to collide with each other more often because a. they are large with respect to their separations b. they occur in clusters c. both of these 58. The radio lobes that flank some radio galaxies produce mainly a. 21-cm radiation b. synchrotron radiation c. black body radiation 59. The central galaxy in a double-lobed radio source is usually a. an irregular galaxy b. a spiral galaxy c. a dwarf elliptical galaxy d. a giant elliptical galaxy 60. If the red shifts of quasars arise from the expansion of the universe, then a. quasars must be very small b. quasars must be very luminous c. quasars must be local 61. Quasars must be small, because they a. have high radial velocities b. are very luminous c. are surrounded by quasar fuzz d. fluctuate rapidly

8 62. Which of the following is not a characteristic of spiral galaxies? a. a nuclear bulge b. a flat disk c. a halo of old stars d. a, b, and c are all characteristics of spiral galaxies 63. The local cluster of galaxies contains about how many members? a. 4 b. 30 c. 200 d The largest galaxies known to be members of the local cluster are: a. the Milky Way and the Andromeda Galaxies b. the Milky Way and the Magellanic Clouds c. the Magellanic Clouds d. Hodge Distances to the nearest galaxies were first determined using which of the following indicators? a. Trigonometric parallax b. Main-sequence fitting c. Cepheid variables d. The Hubble relation 66. When we measure the Doppler shifts of galaxies in the local cluster we find: a. they are all moving away from us with speeds proportional to their distances. b. some are moving toward us and some are moving away from us. c. all are moving toward us. d. the spectral lines so diffuse that Doppler measurements are impossible. 67. Hubble's law for galaxies relates: a. distance and radial velocity for galaxies outside the local cluster. b. distance and mass for galaxies of the local cluster. c. distance and red shift for galaxies of the Virgo cluster. d. radial velocity and absolute magnitude for all galaxies. 68. Which of the following is true of quasar spectra? a. They show no identifiable spectral lines. b. They show highly red-shifted spectral lines similar to those of a class M main-sequence star. c. They show highly red-shifted emission lines of hydrogen. d. They show highly red-shifted absorption lines of hydrogen. 69. What do high positive z values indicate? a. The distance between us and the source is rapidly decreasing. b. The distance between us and the source is rapidly increasing. c. The source is moving rapidly in an unknown direction. d. The source is at a very great distance. 70. Which of the following is not true of quasars? a. They all show very large red shifts. b. They are all radio sources. c. Some of them show disks with the same red shifts. d. They look much like the cores of some active galaxies.

9 71. The local cluster has more of which type of galaxy? a. Elliptical b. Spiral c. Barred spiral d. Irregular 72. The nearest large cluster of galaxies is which of the following? a. The Coma Cluster b. The Virgo Cluster c. NGC 205 d. The Perseus-Pegasus Cluster 73. Which of the following is not a part of the study of cosmology? a. The evolution of the universe b. The effect of the universe on the everyday lives of humans c. The organization of the universe d. The study of the origin of the universe 74. Which of the following do not constitute a part of the observational evidence supporting the big bang theory of the universe? a. Hubble's law b. The 3K microwave background radiation c. The chemical abundances in the universe d. All of the above support the big bang theory of the universe. 75. According to the big bang theory about how old is the universe? a. About 100 million years b. About 13 billion years c. About 500 billion years d. The big bang theory does not predict the age of the universe. 76. Nearly all of the elements heavier than hydrogen and helium were formed: a. during the first few minutes after the big bang. b. immediately after decoupling. c. after about 100 thousand years. d. only after stars formed. 77. To say that red shifts are cosmological means: a. they are related to recessional velocity. b. they are related to distance through the Hubble relation. c. they are being observed for celestial objects. d. astronomers use red shifts to describe what happened in the first few minutes after the big bang. 78. The Hubble constant is: a. equal to the age of the universe. b. the same as the Hubble time. c. the proportionality constant that relates recessional velocity and distance. d. the proportionality constant that relates time with the density of the universe. 79. The Hubble time is: a. the time required for decoupling of the early universe.

10 b. the time required for the expansion of the universe to reverse. c. the "relaxation time" required for the onset of galaxy formation. d. an upper limit to the age of the universe. 80. If the Hubble constant has a value of 50 km/s/mpc the Hubble time is about: a. 20 million years. b. 200 million years. c. 20 billion years. d. 200 billion years

11 True/False 87. The interstellar medium can make distant stars look redder than they really are. 88. The thermal motions of the atoms in a gas cloud can make it collapse to form a protostar. 89. Ninety percent of all stars burn helium and lie on the main sequence. 90. Hydrogen fusion does not change the number of atoms in a star s core. 91. A 6 solar mass star will remain on the main sequence for about 12 billion years. 92. Stars swell into giants when hydrogen is exhausted in their centers. 93. Helium fusion reactions combine two helium nuclei to make one carbon nucleus. 94. The helium flash is the cause of some supernovae. 95. Helium burning does not begin until the star has entered the giant region of the H-R diagram. 96. The orbital period of our sun is approximately 240 million years. 97. White dwarfs are about the mass of the sun and the diameter of the earth. 98. Novae are always associated with white dwarfs. 99. Pulsars could not be pulsating stars because the pulses are too short W e expect neutron stars to spin rapidly because they conserve angular momentum. 64. Many pulsars have periods that are gradually in creasing as the spinning neutron stars lose energy. 65. The event horizon marks the boundary within which the density is roughly the same as that of the atomic nucleus. 66. Theory predicts that neutron stars may not exceed 2 to 3 solar masses. 67. If the accretion disk around a black hole emits x-rays outside the event horizon, the x-rays can escape. 69. Cepheid variable stars are more luminous than the sun. 70. Some large clusters of galaxies do not appear to contain enough mass to hold themselves together. 72. The disk of the Milky Way is about 20,000 light-years in diameter. 74. Giant molecular clouds are located in spiral arms. 77. Double-lobed radio galaxies appear to be emitting jets of gas and radiation. 78. The radio radiation emitted by a radio lobe is mainly synchrotron radiation. 79. Seyfert galaxies are spiral galaxies with active cores. 80. Quasar red shifts are usually larger than the red shifts of the visible galaxies.