A) X-rays are emitted by the hot gas in the accretion disk.
B) The accretion disk consists of material that spills off the companion star.
C) The compact object may be either a neutron star or a black hole.
D) Several examples of flattened accretion disks being "fed" by a large companion star can be seen clearly in photos from the Hubble Space Telescope.
E) The radiation from an accretion disk may vary rapidly in time.
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A) the remains of a star that died in a massive star supernova (if no black hole was created)
B) the remains of a star that died by expelling its outer layers in a planetary nebula
C) a star made mostly of elements with high atomic mass numbers, so that they have lots of neutrons
D) an object that will ultimately become a black hole
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A) 0.5 solar masses
B) 1.4 solar masses
C) 3 solar masses
D) 10 solar masses
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A) New stars forming in the Milky Way.
B) Supernovae in the Milky Way.
C) Very powerful supernovae occurring in distant galaxies.
D) The collision of stars in the dense nuclei of distant galaxies.
E) It is not known but it may be the collision of a neutron star with a black hole.
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A) an O star
B) a star like our Sun
C) a binary M star
D) a white dwarf star with a red giant binary companion
E) a pulsar
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A) It gradually spirals into the star.
B) It settles into a smaller orbit, with similar distance from the surface as the original orbit.
C) It remains in the same orbit.
D) It is instantly ejected from its orbit.
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A) The entire Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star.
B) It would rapidly sink to the center of Earth.
C) The combined mass of Earth and the neutron star would cause the neutron star to collapse into a black hole.
D) It would crash into Earth, throwing vast amounts of dust into the atmosphere that, in turn, would cool the Earth; this is probably what caused the extinction of the dinosaurs.
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A) neutron degeneracy pressure
B) electron degeneracy pressure
C) thermal pressure
D) radiation pressure
E) all of the above
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A) An object with gravity so strong that not even light can escape
B) A dead star that has faded from view
C) Any object made from dark matter
D) A compact mass that emits no visible light
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A) The accretion disk around a neutron star is much hotter and emits higher-energy radiation.
B) The accretion disk around a neutron star is made mostly of helium while the accretion disk around a white dwarf is made mostly of hydrogen.
C) The accretion disk around a neutron star is more likely to give birth to planets.
D) The accretion disk around a neutron star always contains much more mass.
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A) nothing.
B) a neutron star or black hole.
C) a white dwarf.
D) newborn star.
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A) only the mass of the black hole
B) the observationally measured radius of the black hole
C) the way in which the black hole formed
D) both the mass and chemical composition of the black hole
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A) The white dwarf undergoes a collapse and expels the excess mass in a nova eruption.
B) The white dwarf (which is made mostly of carbon) suddenly detonates carbon fusion and this creates a white dwarf supernova explosion.
C) The white dwarf immediately collapses into a black hole, disappearing from view.
D) A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the accreting material from reaching it in the first place.
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A) If you watch someone else fall into a black hole, you will never see him or her cross the event horizon. However, he or she will fade from view as the light he or she emits becomes more and more redshifted.
B) If we watch a clock fall toward a black hole, we will see it tick slower and slower as it falls towards to the black hole.
C) The event horizon of a black hole represents a boundary from which nothing can escape.
D) 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.
E) If you fell into a supermassive black hole (so that you could survive the tidal forces) , you would experience time to be running normally as you plunged across the event horizon.
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A) It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.
B) It is the "point of no return" of the black hole; anything closer than this point will not be able to escape the gravitational force of the black hole.
C) It is the edge of the black hole, where one could leave the observable universe.
D) The term is intended to emphasize the fact that an object can become a black hole only once, and a black hole cannot evolve into anything else.
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A) hydrogen fusion on the surface of a white dwarf
B) carbon fusion in the core of a white dwarf
C) hydrogen fusion on the surface of a neutron star
D) a white dwarf that gains enough mass to exceed the 1.4-solar-mass limit
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A) a small asteroid (10 km in diameter)
B) Earth
C) the Moon
D) Jupiter
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A) A massive-star supernova is brighter than a white-dwarf supernova.
B) A massive-star supernova happens only once, while a white-dwarf supernova can repeat periodically.
C) The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not.
D) The light of a white-dwarf supernova fades steadily, while the light of a massive-star supernova continues to brighten for many weeks.
E) We cannot yet tell the difference between a massive-star supernova and a white-dwarf supernova.
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White-dwarf supernovae occur when the ma...View Answer
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A) White dwarfs come only from stars with masses less than 1.4 solar masses.
B) 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, and no more mass can be supported.
C) The more massive the white dwarf, the higher its temperature and hence the greater its degeneracy pressure. Near 1.4 solar masses, the temperature becomes so high that all matter effectively melts into subatomic particles.
D) The upper limit to the masses of white dwarfs was determined through observations of white dwarfs in binary systems, but no one knows why the limit exists.
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