HW4 – Space – Flashcards
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that the carbon, oxygen, and many elements essential to life were created by nucleosynthesis in stellar cores
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What did Carl Sagan mean when he said that we are all "star stuff"?
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low-mass star
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What type of star is our Sun?
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between 8 and 100 solar masses
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What is the range of star masses for high-mass stars?
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its surface temperature increases and its luminosity decreases
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As a solar mass protostar moves on to the main sequence
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when the rate of hydrogen fusion within the star's core is high enough to sustain gravitational equilibrium
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When does a star become a main-sequence star?
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Its core contracts, but its outer layers expand and the star becomes bigger and brighter
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What happens when a star exhausts its core hydrogen supply?
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cooler and brighter.
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Compared to the star it evolved from, a red giant is
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100 million K
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At approximately what temperature can helium fusion occur?
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3
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How many helium nuclei fuse together when making carbon?
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the expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star
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What is a planetary nebula?
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It becomes a white dwarf.
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What happens to the core of a star after a planetary nebula occurs?
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protostar, main-sequence, red giant, white dwarf
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Which of the following sequences correctly describes the stages of life for a low-mass star?
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hotter and dimmer.
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Compared to the star it evolved from, a white dwarf is
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iron
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Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?
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The core contracts and becomes a black hole
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What happens when the gravity of a massive star is able to overcome neutron degeneracy pressure?
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stars that are at least several times the mass of the Sun
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What types of stars end their lives with supernovae?
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Each successive stage lasts for approximately the same amount of time.
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) Which of the following statements about stages of nuclear burning (i.e., first-stage hydrogen burning, second-stage helium burning, etc.) in a massive star is not true?
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the sudden collapse of an iron core into a compact ball of neutrons
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Which event marks the beginning of a supernova?
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either a neutron star or a black hole
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After a supernova event, what is left behind?
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The giant must once have been the more massive star but transferred some of its mass to its companion.
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You discover a binary star system in which one member is a15MSun main-sequence star and the other star is a 10MSun giant. How do we believe that a star system such as this might have come to exist?
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the Sun
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Which of the following is closest in mass to a white dwarf?
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The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, so more mass cannot be added without breaking the degeneracy pressure.
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Why is there an upper limit to the mass of a white dwarf?
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It will cool down and become a cold black dwarf.
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What is the ultimate fate of an isolated white dwarf?
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The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy.
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Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit?
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Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5 billion years from now.
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Which of the following statements about novae is not true?
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electron degeneracy pressure
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What kind of pressure supports a white dwarf?
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1.4 solar masses
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What is the upper limit to the mass of a white dwarf?
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It has a smaller radius
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How does a 1.2-solar-mass white dwarf compare to a 1.0-solar-mass white dwarf?
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the earth
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Which of the following is closest in size (radius) to a white dwarf?
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a white dwarf star with a red giant binary companion
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What kind of star is most likely to become a white-dwarf supernova?
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The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not.
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Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?
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more than Mt. Everest.
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A teaspoonful of neutron star material on Earth would weigh
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a city
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Which of the following is closest in size (radius) to a neutron star?
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an object that emits flashes of light several times per second or more, with near perfect regularity
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From an observational standpoint, what is a pulsar?
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a rapidly rotating neutron star
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From a theoretical standpoint, what is a pulsar?
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As the star spins, beams of radio radiation sweep through space. If one of the beams crosses the earth, we observe a pulse.
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What causes the radio pulses of a pulsar?
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any object from which the escape velocity equals the speed of light
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What is the basic definition of a black hole?
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If the Sun magically disappeared and was replaced by a black hole of the same mass, the earth would soon be sucked into the black hole.
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Which of the following statements about black holes is not true?
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a white dwarf
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If you were to come back to our Solar System in 6 billion years, what might you expect to find?
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because the current evidence suggests that they are the most powerful bursts of energy that ever occur anywhere in the universe, but we don't know how they are produced
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Why do astronomers consider gamma-ray bursts to be one of the greatest mysteries in astronomy?
