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Home , Absolute magnitude, Apparent magnitude, Electra (star), Giant star, Helium flash, Maia (star)

1 101.002

Hour Exam 3

April 13, 2009

Answers Given in BOLD FACE

QUESTION 1: The produces energy by what kind of reaction? a) Burning (a chemical reaction). b) Fusion. c) Fission. d) . e) . QUESTION 2: A fusion reaction results in: a) The building up of heavier nuclei from nuclei. b) The breaking apart of heavy nuclei into lighter ones. c) The annihilation of nuclei. d) The annihilation of . e) dioxide. QUESTION 3: The most tightly bound nucleus is: a) . b) . c) Carbon. d) . e) Uranium. QUESTION 4: Fusion reactions release energy by: a) Converting into energy. b) Reducing nuclear binding energies. c) Creating simpler forms of matter. d) Producing . e) The weak nuclear force. QUESTION 5: The present level of the production of energy on the Sun results in a) The Sun getting less massive. b) The Sun getting more massive. c) The Sun getting hotter. d) The Sun getting cooler. e) The Sun rotating faster. QUESTION 6: Fusion occurs only near the Sun’s center because: a) Only near the center is there enough hydrogen that is not mixed with other elements. b) Only near the center is the favorable for fusion. c) Heat is transferred down to the center to ignite fusion. d) Only at the center are the and pressure high enough to sustain fusion. e) The statement is false: fusion occurs throughout the Sun.

2 QUESTION 7: The mass of a can be determined by: a) Measuring its b) Determining its composition. c) Measuring its color. d) Measuring its Doppler shift. e) Studying its orbit around a binary companion. QUESTION 8: Cool can be very luminous if they are: a) Small. b) Hot. c) Large. d) Close to our . e) In a binary system. QUESTION 9: The color of a star is most directly related to its: a) Mass. b) Surface temperature. c) Core temperature. d) Luminosity. e) . QUESTION 10: Which of the following properties of stars can be determined without knowing the star- distance? a) Luminosity. b) Density. c) Radius. d) . e) Surface temperature. QUESTION 11: If the star α-Cygni were twice as far away as it actually is, its absolute luminosity would change by what factor? a) Double. b) Four times. c) One-half. d) One-quarter. e) Unchanged. QUESTION 12: If two stars have the same radius but different , then the hotter star will be: a) Bluer and brighter. b) Redder and brighter. c) Bluer and fainter. d) Redder and fainter. e) Redder but the same . QUESTION 13: The difference between a star’s absolute and is a measure of its: a) Distance. b) Temperature. c) Luminosity. d) Mass. e) Color.

3 QUESTION 14: If two stars are observed with the same apparent brightness and are not obscured by dust or gas, then a) They have the same temperature. b) They are the same distance from us. c) They have the same angular size. d) The further one must have a greater luminosity. e) They have the same luminosity. QUESTION 15: The region of the H-R diagram occupied by the most stars is the: a) region. b) dwarf region. c) giant region. d) Hot star region. e) Cool star region. QUESTION 16: construct a Hertzsprung-Russell diagram from observed stars by plotting: a) Apparent brightness and distance. b) Distance and color. c) Size and surface temperature. d) Luminosity and distance. e) Luminosity and surface temperature. QUESTION 17: The visual magnitude of star, by itself, is a good indicator of: a) Its actual brightness. b) Its surface temperature. c) Its distance. d) Its size. e) Nothing. QUESTION 18: Star A appears blue and star B appears red. What do we know for sure? a) Star A is hotter than star B. b) Star A is cooler than star B. c) Star A is more luminous than star B. d) Star A is less luminous than star B. e) Star A is larger than star B. QUESTION 19: We know that giant stars are larger in diameter than main sequence stars even though we cannot directly measure their size because: a) They are more luminous for the same temperature. b) They are less luminous for the same temperature. c) They are hotter for the same luminosity. d) They are brighter for the same luminosity. e) They are more distant for the same luminosity. QUESTION 20: The physical property that most uniquely determines where a star will be on the main sequence is its a) Age. b) Distance. c) Mass. d) Size. e) Relative hydrogen abundance.

4 QUESTION 21: The coolest main-sequence stars have a surface temperature of approximately: a) 300 K. b) 3000 K. c) 6000 K. d) 10,000 K. e) Absolute zero. QUESTION 22: A is a) A system containing a . b) A rotating white dwarf. c) A rotating . d) A rotating star. e) A rotating star. QUESTION 23: Two stars are each observed in January and again in July. Star A has a of 1.03”, while the Star B has a parallax of 1.70”. What can you conclude? a) Star A is brighter than Star B. b) Star A is hotter than Star B. c) Star A is more massive than Star B. d) Star A is closer to earth than Star B. e) Star B is closer to earth than Star A. QUESTION 24: , the “dog star”, is a distance of ~2.5 pc from Earth. What can you conclude from this information? a) Sirius has a higher luminosity than the Sun. b) Sirius appears brighter than the Sun. c) Sirius has an observed parallax of 2.5”. d) Sirius has an observed parallax of 0.4”. e) The parallax of Sirius is too small to be measured. QUESTION 25: Sirius has an apparent magnitude of -1.5 and the Sun has an apparent magnitude of -26.7. What can you conclude from this information? a) The Sun appears brighter than Sirius. b) Sirius appears brighter than the Sun. c) Sirius is hotter than the Sun. d) The Sun is hotter than Sirius. e) Sirius is more luminous than the Sun. QUESTION 26: In order for a dark cloud to collapse it must: a) Not be spinning. b) Contain no molecules. c) Be very hot. d) Have a high internal pressure compared with its . e) Have a low internal pressure compared with its gravity. QUESTION 27: The component of the that prevents us from seeing its center is: a) Hot hydrogen gas. b) Cold hydrogen gas. c) A dense concentration of stars. d) Interstellar dust. e) Intergalactic nebulae.

5 QUESTION 28: Interstellar dust can be recognized by its: a) Emission of 21-centimeter . b) Absorption lines. c) Absorption of radio waves. d) Bright colors e) Blocking of . QUESTION 29: If Star A has a radius twice as large as that of Star B, and the surface of Star B is twice as hot as Star A, which of the following must be true? a) Star A has a higher luminosity. b) Star B has a higher luminosity. c) The stars have the same luminosity. d) The stars have the same visual magnitude. e) None of the above. QUESTION 30: The is composed mostly of: a) Hydrogen and helium b) Hydrogen and . c) Nitrogen and oxygen. d) Metallic hydrogen. e) Dust. QUESTION 31: Given the following apparent magnitudes, which star looks the brightest? a) – magnitude 2.86. b) – magnitude 3.62. c) – magnitude 3.7. d) – magnitude 3.86. e) – magnitude 5.64. QUESTION 32: Evidence for interstellar material is: a) The motion of stars slows down over time. b) Distant stars have large Doppler red shifts. c) Distant stars appear reddened. d) Most apparently bright stars are far from us. e) There is no way to detect the interstellar medium. QUESTION 33: The speed necessary to escape a black hole is: a) Infinite. b) Undefinable. c) Greater than or equal to the velocity of light. d) Less that but almost equal to the velocity of light. e) Greater than or equal to the velocity of sound. QUESTION 34: If two stars are the same size, which of the following must be true? a) The hotter star appears to be brighter. b) The hotter star appears to be bluer. c) The hotter star appears to be redder. d) The closer star appears to be brighter. e) The closer star appears to be bluer. QUESTION 35: In , gravity results in: a) Curved time. b) Curved space. c) . d) The strong nuclear force. e) The . 6 QUESTION 36: The main energy source in the star , a red giant, is which process? a) Nuclear fusion. b) . c) . d) Combustion of hydrogen. e) A red giant does not produce any energy. QUESTION 37: A star on the main sequence maintains its size for a long time because of: a) Equilibrium between its degenerate pressure and its . b) Equilibrium between its energy generated by fusion and its luminosity. c) Equilibrium between its and convection. d) Equilibrium between its outward pressure and gravity. e) The statement is false – the star is constantly getting smaller. QUESTION 38: The most massive stars are believed to end up as: a) . b) -ray bursts. c) Black holes. d) Neutron stars. e) Planetary nebulae. QUESTION 39: A cloud fragment with a mass of 0.02 times the mass of the Sun will evolve into what? a) A white dwarf. b) A black hole. c) A main sequence star. d) A . e) A . QUESTION 40: The correct past, present & future sequence of stages in the of the Sun is: a) , main sequence star, red giant, planetary , white dwarf. b) Protostar, main sequence star, red supergiant, , . c) Protostar, main sequence star, , red giant, white dwarf. d) Protostar, main sequence star, planetary nebula, red giant, . e) We can’t predict what will happen in the future to the Sun. QUESTION 41: The found on Earth came from: a) A supernova. b) A nova. c) Nuclear fusion in a star. d) Nuclear fission in a star. e) Chemical reactions after the Earth was formed. QUESTION 42: An isolated white dwarf produces energy by: a) Nuclear fusion. b) Nuclear fission. c) Gravitational collapse. d) Radiation pressure. e) A white dwarf does not produce energy.

7 QUESTION 43: As a one-solar-mass star evolves to the red giant stage: 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 surface temperature decreases and its luminosity increases. e) Its radius gets larger but its temperature remains the same. QUESTION 44: Which of the following stars will spend the longest time on the main sequence? a) A 10 solar-mass star. b) A 4 solar-mass star. c) The Sun. d) A 0.5 solar-mass star. e) A red . QUESTION 45: The fusion of helium in a star’s core: a) Only takes place rapidly during the . b) Requires higher temperature than Hydrogen fusion because nuclei with more repel each other more strongly. c) Takes place at a lower temperature than Hydrogen fusion as Helium nuclei are more massive. d) Causes the star’s core to stabilize due to the Pauli Exclusion Principle. e) Burns longer than it took to burn up the Hydrogen. QUESTION 46: A planetary nebula is: a) An expanding shell from a dying star. b) A cloud of gas from which stars will form. c) A cloud of cold dust in space. d) Several close by faint members of the . e) A circular ring around a black hole. QUESTION 47: A nova can result from: a) The fusion of iron in the core of a massive star. b) The fall of material onto a black hole from a white dwarf. c) The collapse of a protostar. d) The transfer of material onto a white dwarf in a binary . e) The collapse and bounce from a dying giant star. QUESTION 48: A is very dense meaning it has: a) A very large mass. b) Great opacity. c) No charge. d) Great mass for its volume. e) A small size. QUESTION 49: If the Sun were magically to turn into a black hole of the same mass: a) The Earth would start to spiral inward. b) The Earth would be quickly sucked into the black hole. c) The Earth’s orbit would be unchanged. d) The Earth would fly off into space. e) The Earth would be torn apart by the black hole’s gravitational field.

8 QUESTION 50: Why aren’t all neutron stars observed as pulsars? a) Some neutron stars don’t rotate. b) Most neutron stars are too far away. c) Many neutron stars don’t emit beams of radiation. d) Some neutron stars are too massive for light to escape. e) Only some neutron stars are oriented so that their emission beams sweep past the Earth. QUESTION 51: Which of the following was an early test of General Relativity? a) The spin-up of millisecond pulsars. b) The bending of light from the Sun’s gravitational field observed in a total solar . c) The lighthouse model of a pulsar. d) The afterglow from a gamma-ray burst. e) The Michelson-Morley experiment. QUESTION 52: Black holes result from which phenomenon? a) Collapse of neutron stars with greater than 3 solar masses. b) Novae. c) Helium flash. d) Core collapse of a 1 solar-mass star. e) Pulsar spin-up. QUESTION 53: Place the following objects in order of increasing density: a) Neutron star, white dwarf, black hole. b) Neutron star, black hole, white dwarf. c) White dwarf, neutron star, black hole. d) White dwarf, black hole, neutron star. e) Black hole, neutron star, white dwarf. QUESTION 54: A globular cluster helps astronomers study because: a) All of the stars are the same distance from the Earth. b) All of the stars are the same age. c) All of the stars have the same mass. d) All of the stars have the same temperature. e) All of the stars are in binaries. QUESTION 55: What phenomenon causes a supernova in a high-mass star? a) Core collapse following fusion of lighter elements into iron. b) A helium flash. c) of matter from a companion star. d) Collapse of a neutron star. e) Accumulation of uranium in the core causing a nuclear explosion. QUESTION 56: How does a nova differ from a supernova? a) A nova occurs in a red giant star while a supernova occurs in a red . b) A nova occurs in a binary star system while a supernova occurs only in an isolated star. c) A nova always leaves a neutron star behind while a supernova always leaves behind a black hole. d) A nova occurs on the surface of a star while a supernova involves the entire star. e) The only difference is that a supernova is bigger than a nova. 9 QUESTION 57: What phenomenon is responsible for the 21-centimeter line in radio emission? a) in the first excited state in hydrogen atoms relax to the ground state. b) Doubly ionized oxygen makes a molecular transition. c) Electrons in atomic hydrogen flip their spin from parallel to antiparallel to the spin of the protons. d) The in metallic hydrogen flips its spin. e) An embedded star causes the gas of an emission nebula to glow.

QUESTION 58: The 11- refers to what phenomenon? a) The period of rotation of the Sun. b) The apparent motion of the Sun in the . c) The rate of production in the Sun’s core. d) The temperature of the . e) The occurrence of magnetic storms on the solar surface. QUESTION 59: For what reason do astronomers want to measure neutrino production from the Sun? a) The neutrinos are more energetic than photons. b) Neutrinos are easier to detect than photons. c) Neutrinos give direct information about the . d) Neutrinos give direct information about the Sun’s core. e) Neutrinos give information about magnetic storms. QUESTION 60: look dark because they are: a) Coronal holes. b) Cooler than the photosphere. c) Regions with lower hydrogen concentration. d) Regions with magnetic poles. e) Circulating.