Phys 0 Astronomy (Dr. Ilias Fernini) Review Questions for Chapter 9 MULTIPLE CHOICE 1. We know that giant stars are larger in diameter than the sun because * a. they are more luminous but have about the same temperature. b. they are less luminous but have about the same temperature. c. they are hotter but have about the same luminosity. d. they are cooler but have about the same luminosity. e. they have a larger absolute magnitude than the sun. 2. Giant stars are I. more luminous than the sun. II. larger in diameter than the sun. III. cooler than B stars. IV. located above the main sequence stars in the H-R diagram. a. I & II b. II & IV c. I, II, & IV d. II, III, & IV * e. I, II, III, & IV Use the following HR diagram to answer the next three questions: +6 +4 +2 Luminosity 1 Alnilam HR 5337 Arcturus Antares -2 Sirius B -4 O B A F G K M Spectral Type 3. Which star in the diagram above is most like the sun? a. Alnilam b. Antares c. Arcturus * d. HR 5337 e. Sirius B 4. Which star in the diagram above has the greatest surface temperature? 1
* a. Alnilam b. Antares c. Arcturus d. HR 5337 e. Sirius B 5. Which of the stars in the diagram above has the largest radius? a. Alnilam * b. Antares c. Arcturus d. HR 5337 e. Sirius B 6. In an H-R Diagram, stars with the smallest radius are found in the of the diagram. a. center b. upper left corner c. upper right corner * d. lower left corner e. lower right corner 7. Spectroscopic and eclipse duration observations of an eclipsing binary star can enable astronomers to calculate of its individual stars. a. the masses b. the sizes * c. both a and b d. neither a nor b 8. Doppler shift observations of a spectroscopic binary star can enable astronomers to calculate of its individual stars. * a. the masses b. the sizes c. both a and b d. neither a nor b 9. Binary (double) stars can be detected by a. being seen as two separate stars with a telescope. b. one star traveling a wiggly proper motion path across the sky. c. one star dimming abruptly as another passes in front of it. d. pairs of absorption lines seen in the spectrum of what appears to be one star. * e. all of the above. The binary star, Mizar A, is shown with the motion of the members around one another. The mass of a visual binary pair of stars can be obtained from a. the time in years for them to orbit one another. b. the size of their orbit. c. their location in space. * d. both a and b 11. We know the white dwarf star Sirius B has a mass comparable to the Sun because of a. its measured color b. its measured temperature compared to Sirius A 2
* c. it is part of binary star system with Sirius A. 12. In the H-R diagram, 90 percent of all stars are a. in the giant region. b. in the supergiant region. c. among the B stars. d. among the G stars. * e. on the main sequence. 13. The most common stars are a. supergiants. b. giants. c. upper main sequence stars. d. white dwarfs. * e. lower main sequence stars. 14. In the list below, the least common stars are * a. upper main sequence stars. b. white dwarfs. c. lower main sequence stars. 15. If two stars are emitting the same amount of light, the star that is farther will appear a. brighter. * b. dimmer. c. redder. d. bluer. e. They will have the same brightness as seen from Earth. 16. How can we tell that some stars are relatively close to us in the sky? a. Some stars are occasionally eclipsed by the Moon, so they must be nearby. b. Some stars vary in brightness caused by sunspots we can see because they are so close. c. Some stars appear to be extremely bright and must therefore be very close to us. * d. Some stars appear to move periodically back and forth against the background stars because of the Earth's movement around the Sun 17. Stars in the upper right part of the Hertzsprung-Russell diagram are always when compared to stars near the middle of the diagram. a. cooler b. brighter as seen from Earth. * c. larger. d. smaller. e. more massive. 18. You are standing near a railroad track and a train is moving toward you at 60 mph and blowing his horn. What will you notice as the train moves past you? a. As the train approaches, the horn will sound lower in pitch than when it is moving away. * b. As the train approaches, the horn will sound higher in pitch than when it is moving away. c. There will be no change in the pitch of the horn as it moves by. d. The horn will get louder as the train moves away from me. e. The horn will get quieter as the train moves toward me 3
19. The table below lists the spectral types for each of five stars. Which star in this table would have the lowest temperature? a. For Star Name Spectral Type * b. Cet For F8 c. 35 Ari Cet M7 d. Tri 35 Ari B3 e. Per Tri A0 Per O7 20. The table below lists the spectral types for each of five stars. Which star in this table would have the highest temperature? a. For Star Name Spectral Type b. Cet For F8 c. 35 Ari Cet M7 d. Tri 35 Ari B3 * e. Per Tri A0 Per O7 21. What is the order of star colors with increasing temperature? * a. Red, Yellow, Blue b. Blue, Red, Yellow c. Red, Blue, Yellow d. Yellow, Red, Blue e. Blue, Yellow, Red 22. The Doppler effect states that the motion of any object can * a. shift the wavelength of spectral lines. b. change the speed of light emitted from the object. c. enhance the chemical composition of the object. d. make the object appear hotter. e. make the object appear cooler. 23. Which of the following stars is the hottest based on spectral classification alone? * a. B5 b. A2 c. F7 d. M1 e. A8 4
24. Interstellar gas clouds may collapse to form stars if they a. have very high temperatures. * b. encounter a shock wave. c. rotate rapidly. d. are located near main sequence spectral type K and M stars. e. all of the above 25. The diagram to the right is an HR diagram. The line indicates the location of the main sequence. Which of the five labeled locations on the HR diagram indicates a luminosity and temperature similar to that of a T Tauri star? a. 1 b. 2 c. 3 * d. 4 e. 5 0,000,000 00 0 Luminosity 1 0.1 0.01 2 5 4 3 1 20,000,000 5000 2500 Temperature 26. The free-fall contraction of a molecular cloud * a. can be initiated by shock waves from supernovae. b. can be initiated by nearby spectral type G stars. c. can be initiated by the rotation of the cloud. d. causes the cloud to become transparent to ultraviolet radiation. e. causes the particles in the cloud to decrease the speed with which they move. 27. The proton-proton chain needs high temperature because a. of the ground state energy of the hydrogen atom. b. of the presence of helium atoms. * c. the protons must overcome the Coulomb barrier. d. of the need for low density. e. the neutrinos carry more energy away than the reaction produces. 28. is the thermonuclear fusion of hydrogen to form helium operating in the cores of massive stars on the main sequence. * a. The CNO cycle b. The proton-proton chain c. Hydrostatic equilibrium d. The neutrino process e. none of the above 29. If the sun produces energy by the proton-proton chain, then the center of the sun must have a temperature of at least a. 4 K * b. 7 K c. K d. 13 K e. 16 K 5
30. The carbon-nitrogen-oxygen cycle a. operates at a slightly lower temperature than the proton-proton chain. b. is most efficient in a star less massive than the sun. c. occurs when carbon and oxygen combine to form nitrogen, which produces energy. d. produces the energy responsible for bipolar flows. * e. combines four hydrogen nuclei to form one helium nucleus, which produces energy. 31. The region of the sun just below the photosphere a. is undergoing thermonuclear fusion using the proton-proton chain. b. is undergoing thermonuclear fusion using the CNO cycle. * c. is transporting energy to the photosphere by convection. d. is not in hydrostatic equilibrium. e. a and c above 32. The central cores of massive main sequence stars a. produce energy by the proton-proton chain. b. have a very low opacity. * c. transmit energy outward by convection. d. burn their nuclear fuels more slowly than low mass main sequence stars. e. have lower temperatures than the central cores of low mass main sequence stars. 33. While on the main sequence a star s primary energy source comes from * a. nuclear fusion. b. nuclear fission. c. gravitational potential energy. d. magnetic fields. 34. As a star begin to form the initial energy source is from a. nuclear fusion. b. nuclear fission. * c. gravitational potential energy. d. magnetic fields. 35. The lowest-mass stars cannot become giants because a. they do not contain helium. b. they rotate too slowly. * c. they cannot heat their centers hot enough. d. they contain strong magnetic fields. e. they never use up their hydrogen. 36. A planetary nebula is * a. the expelled outer envelope of a medium mass star. b. produced by a supernova explosion. c. produced by a nova explosion. d. a nebula within which planets are forming. e. a cloud of hot gas surrounding a planet. 37. The Chandrasekhar limit tells us that a. accretion disks can grow hot through friction. b. neutron stars of more than 3 solar masses are not stable. c. white dwarfs must contain more than 1.4 solar masses. 6
* d. not all stars will end up as white dwarfs. e. stars with a mass less than 0.5 solar masses will not go through helium flash. 38. The Chandrasekhar limit is solar masses. a. 0.014 b. 0.14 * c. 1.4 d. 14 39. The energy a white dwarf emits into space is a. replaced by fusion of hydrogen atoms into helium. b. replaced by fusion of helium atoms into carbon. * c. not replaced. 40. A Type I supernova is believed to occur when a. the core of a massive star collapses. b. carbon detonation occurs. * c. a white dwarf exceeds the Chandrasekhar limit. d. the cores of massive stars collapse. e. neutrinos in a massive star become degenerate and form a shock wave that explodes the star. 41. A nova is almost always associated with a. a very massive star. b. a very young star. c. a star undergoing helium flash. * d. a white dwarf in a close binary system. e. a solar like star that has exhausted its hydrogen and helium. 42. As material leaves an expanding star and begins to fall into a white dwarf * a. an accretion disk will form around the white dwarf. b. the material will cool off because it begins to move at high velocities. c. the material will fall directly onto the surface of the white dwarf. d. the white dwarf will produce a type-ii supernova. e. the white dwarf's radius will increase. 43. In A.D. 54, Chinese astronomers observed the appearance of a new star, whose location is now occupied by a. a globular cluster. b. a planetary nebulae. c. a white dwarf. d. a young massive star. * e. a supernova remnant. 44. Massive stars cannot generate energy through iron fusion because a. iron fusion requires very high density. b. stars contain very little iron. c. no star can get hot enough for iron fusion. * d. iron is the most tightly bound of all nuclei. e. massive stars supernova before they create an iron core. 45. Stars with masses between 0.4 M and 4 M 7
* a. undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon. b. undergo thermonuclear fusion of hydrogen, but never get hot enough to ignite helium. c. produce type-i supernovae after they exhaust their nuclear fuels. d. produce type-ii supernovae after they exhaust their nuclear fuels. e. undergo carbon detonation. 46. For a star of Sun-like mass, what is the last stage of the nuclear fusion? a. Hydrogen to helium. * b. Helium to carbon and oxygen. c. Carbon to magnesium. d. Fusion goes all the way up to iron. 47. What are the two longest stages in the life of a one solar mass star? a. Protostar, pre-main sequence. b. Protostar, white dwarf. c. Protostar, main-sequence. * d. Main-sequence, white dwarf. 48. What mechanism does an isolated white dwarf use to generate energy? a. Proton-proton chain b. CNO cycle c. Triple alpha process * d. White dwarfs don t generate their own energy. 49. Stars that have ejected a planetary nebula eventually become a. protostars. b. brown dwarfs. * c. white dwarfs. d. red giants. 50. After what evolutionary stage does a star become a white dwarf? a. Protostar b. Pre-main sequence c. Main sequence * d. Giant 51. Where are elements heavier than iron primarily produced? a. Brown dwarfs b. White dwarfs c. Supergiants * d. Supernovae 52. The explosion of a supernova typically leaves behind a. a planetary nebula. b. a shell of hot, expanding gas with a white dwarf at the center. * c. a shell of hot, expanding gas with a pulsar at the center. d. nothing is ever left behind. 8
53. 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 an atomic nucleus. d. about the same as a water molecule. e. smaller than expected because the magnetic field is so strong. 54. A neutron star is expected to spin rapidly because * a. they conserved angular momentum when they collapsed. b. they have high orbital velocities. c. they have high densities. d. they have high temperatures. e. the energy from the supernova explosion that formed them made them spin faster. 55. Although neutron stars are very hot, they are not easy to locate because a. light does not escape from their event horizon. b. most lie beyond dense dust clouds. c. solid neutron material cannot radiate photons. d. they are only found in other galaxies. * e. they have small surface areas. 56. At extremely high densities and temperatures, electrons can be forced to fuse with protons. This reaction produces a. hydrogen. b. Helium and energy. c. degenerate electrons. * d. neutrons and neutrinos. e. large amounts of radio radiation. 57. The density of a is greater than the density of a. a. white dwarf, neutron star b. neutron star, black hole c. pulsar, neutron star * d. pulsar, white dwarf e. white dwarf, black hole 58. A pulsar requires that a neutron star I. rotate rapidly. II. have a radius of at least km. III. have a strong magnetic field. IV. rotate on an axis that is different from the axis of the magnetic field. a. I & III b. I & IV c. II, III, & IV * d. I, III, & IV e. I, II, III, & IV 60. The event horizon a. is believed to be a singularity. b. is a crystalline layer. 9
* c. has a radius equal to the Schwarzschild radius. d. marks the inner boundary of a planetary nebula. e. is located at the point where synchrotron radiation is created around a pulsar. 61. The Schwarzschild radius of a 2 M black hole is approximately * a. 6 km. b. 4 km. c. 2 km. d. 12 km. e. 36 km. 62. 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. c. it would be stationary. * d. very little matter would be falling into it. e. there would be very few stars behind it whose light the black hole could block out. 63. The search for black holes involves a. searching for single stars that emit large amounts of x-rays. * b. finding x-ray binaries where the compact companion has a mass in excess of 3 M. c. searching for large spherical regions from which no light is detected. d. looking for pulsars with periods less than one millisecond. 64. The material that accretes onto a neutron star or black hole is expected to emit x-rays because a. the material will produce synchrotron radiation because of the strong magnetic field. b. hydrogen nuclei begin to fuse and emit high energy photons. * c. the material will become hot enough that it will radiate most strongly at x-ray wavelengths. d. as the material slows down it converts thermal energy to gravitational potential energy. e. none of the above 65. As material flows into a black hole a. the material will experience time dilation. b. the material will become hotter. c. the material will produce an absorption spectrum. d. the material will increase in mass. * e. a and b 66. A black hole can be thought of as a. a very massive object of finite size. b. a shell of material expanding from a white dwarf. * c. a massive body of infinitely small size. d. a burnt out white dwarf. 67. The singularity of a black hole a. is found on the surface of the event horizon. * b. is located at the center of the event horizon. c. can only be located if the black hole is in a binary system. d. doesn t exist since all black holes have a finite size.
68. The escape velocity at the event horizon around a black hole is a. smaller than the speed of light. * b. equal to the speed of light. c. larger than the speed of light. d. irrelevant since nothing (including light) can escape from a black hole. 11