Astronomy CH 18 Concepts Review – Flashcards
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The white dwarf that remains when our sun dies will be mostly made of _______.
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carbon
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the more massive the white dwarf, the ______.
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smaller its radius
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What prevents a white dwarf from having a mass greater than the white dwarf limit (or Chandrasekhar limit)?
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Electron degeneracy pressure depends on the speeds of electrons, and as a white dwarf's mass approaches the white dwarf limit, its electron speeds are already approaching the speed of light.
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According to present understanding, a nova is caused by ______.
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the fusion of hydrogen on the surface of a white dwarf
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Will our Sun ever undergo a white dwarf supernova explosion? Why or why not?
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No, because it's not orbited by another star
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Which of the following best describes what would happen if a 1.5 solar mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your home town?
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The entire mass of the earth would end up as a thin layer, about 1 cm thick, over the surface of a neutron star
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The Voyager spacecraft has a "postcard" designed to be understandable to any aliens that might someday encounter it. On the "postcard," scientists pinpointed the location of Earth by triangulating it between pulsars. Why did the scientists choose pulsars rather than some other type of star?
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Pulsars are easy to identify by their almost perfectly steady periods of pulsation.
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Which statement about pulsars is NOT thought to be true?
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NOT true- Pulsars can form only in close binary systems
TRUE- A pulsar must have a very strong magnetic field and rotate quite rapidly, all pulsars are neutron stars, but not all neutron stars are pulsars, pulsars are kept from collapsing by neutron degeneracy pressure
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Which statement concerning black holes masses and Schwarzschild radii is NOT true?
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NOT true- The maximum mass for a black hole corresponds to one with a Schwarzschild radius of 100 km.
TRUE- Even an object as small as you could become a black hole if there were some way to compress you to a size smaller than your Schwarzschild radius,
The more massive the black hole, the larger the Schwarzschild radius,
For black holes produced in massive star supernovae, Schwarzschild radii are typically a few to a few tens of kilometers
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Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice?
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Time on the clock will run slower as it approaches the black hole, and the light from the clock will be increasingly redshifted
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Which of the following statements about black holes is NOT true?
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NOT True- A spaceship passing near a 10 solar mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar mass main-sequence star.
TRUE- If you fell into a black hole, you would experience time to be running normally as you plunged rapidly across the event horizon,
If you watch someone else fall into a black hole, you will never see them cross the event horizon. However, they will fade from view as the light they emit (or reflect) becomes more and more redshifted.
Although we are not 100% certain that black holes exist, we have strong observational evidence in favor of their existence
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If a neutron star or black hole is accreting material from its companion in a close binary, which of the following observatories would offer us the best chance for discovering this fact?
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Chandra X-Ray observatory
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Which of the following statements about gamma ray bursts is NOT true?
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NOT true- The events responsible for gamma-ray bursts apparently produce ONLY gamma rays, and no other light that we can hope to detect.
TRUE- Based on their distribution in the sky, we can rule out a connection between gamma ray bursts and X-ray binaries in the Milky Way Galaxy.
Gamma ray bursts were originally discovered by satellites designed to look for signs of nuclear bomb tests on Earth.
Gamma ray bursts are apparently among the most luminous events that ever occur in the universe.
