A) The star is a white dwarf in a binary system in which the other star fills its Roche lobe.
B) The star is a neutron star in a binary system in which the other star is a white dwarf.
C) The star is a neutron star in a binary system in which the other star fills its Roche lobe.
D) The star is a black hole in a binary system in which the other star fills its Roche lobe.
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A) at the center of a supernova explosion.
B) in the high-temperature core of a star as it evolves through its main-sequence phase.
C) in a huge gas cloud by collisions between stars.
D) just after the formation of a protostar by gravitational condensation.
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A) The pressure from high-energy photons and neutrinos at the very high core temperatures reached at this stage of development is finally sufficient to halt the collapse.
B) Electrostatic forces between the highly charged iron nuclei are sufficient to overcome the collapse and stabilize the stellar core.
C) Fusion of iron nuclei into heavier nuclei requires energy rather than producing excess energy and therefore will not produce the additional gas pressure to halt the collapse.
D) Iron nuclei are so large that they occupy all remaining space, so the collapse cannot continue.
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A) rapidly rotating neutron star, emitting beams of radio energy and sometimes X-ray and visible energy.
B) binary star in which matter from one star is falling onto the second star.
C) object at the center of each galaxy, supplying energy from its rapid rotation.
D) pulsating star, in which size, temperature, and light intensity vary regularly.
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A) active supernovae
B) globular clusters
C) supermassive black holes
D) quasars
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A) smooth shells of expanding gas.
B) shells that originate from bipolar jets.
C) thousands of clumps of gas.
D) warped rings of gas and dust.
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A) the eclipsing of an X-ray-emitting star with a very hot surface by a cool companion in a close binary system.
B) the pulsation in radius, temperature, and hence luminosity of a hot Cepheid variable star with a surface temperature hot enough to emit X-rays.
C) matter falling violently onto the surface of a rotating neutron star from a close companion in a binary star system, causing an X-ray hot spot that disappears periodically behind the neutron star.
D) matter falling onto the surface of a very hot, rotating white dwarf star from an ordinary companion star in a binary system, producing an X-ray-emitting hot spot that disappears periodically behind the white dwarf.
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A) about 1000 ly.
B) about 1 au.
C) only about 3 to 5 stellar diameters.
D) a few light-years.
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A) A.D. 1604.
B) A.D. 1054.
C) A.D. 1987.
D) A.D. 1572.
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A) mainly carbon and oxygen nuclei supported by electron degeneracy pressure in a volume about the size of the Sun.
B) mostly hydrogen nuclei supported by normal gas pressure due to the very high gas temperature, in a volume about the size of Earth.
C) mainly carbon and oxygen nuclei supported by electron degeneracy pressure in a volume about the size of Earth.
D) mainly helium nuclei supported by electron degeneracy pressure in a volume with a radius about 11 times that of Earth, about the volume of Jupiter.
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A) magnetar.
B) soft gamma-ray repeater.
C) black widow pulsar.
D) X-ray burster.
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A) varies periodically as the neutron star undergoes periodic expansions and contractions.
B) slows down since rotational energy is being used to generate the pulses.
C) speeds up as the neutron star slowly contracts under gravity.
D) remains absolutely constant; pulsars provide ideal frequency standards, or clocks.
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A) A flood of neutrinos is released and pushes outward on the core.
B) A flood of high-energy gamma rays is released and pushes outward on the core.
C) The collapsing core reaches the density of nuclear matter and stiffens.
D) Radioactivity develops because of the tremendous amount of energy available, and the radiation reverses the movement of the core.
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A) black holes, with material falling regularly into them
B) pulsating variable stars
C) rapidly rotating neutron stars
D) rapidly rotating binary star systems in which the stars undergo regular eclipses as seen from Earth
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A) Type Ia supernovae.
B) Type II supernovae
C) supermassive black holes.
D) sources outside the Galaxy that are otherwise unknown.
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A) supernova explosion in the Milky Way Galaxy
B) total eclipse of the Sun over China
C) rare passage of the planet Venus across the face of the Sun, a solar transit
D) discovery of the planet Mercury
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A) hydrogen fusion
B) helium fusion
C) gravitational contraction
D) An isolated white dwarf does not generate energy.
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A) transfer of hydrogen-rich material onto the surface of a white dwarf from its companion in a binary star system
B) helium shell flashes in the helium fusion shell
C) core collapse and the ensuing shock wave
D) collision with another star
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A) at the upper-left end of the main sequence since its surface temperature is extremely high.
B) at the bottom end of the main sequence, along which it has evolved throughout its life.
C) below and to the left of the main sequence.
D) above and to the right of the main sequence since it evolved there after its hydrogen-fusion phase.
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A) Most supernovae produce X-rays and radio waves, not visible light, and were hence invisible to earlier observers.
B) The majority of supernovae must have occurred in the plane of the Milky Way and hence were hidden from Earth by the dense gas and dust in the Milky Way plane.
C) The Milky Way Galaxy is somehow different, with much lower numbers of very massive stars in general, so many fewer stars have undergone supernova explosions.
D) Observers were not watching the sky carefully enough, particularly through the Dark Ages and over the past few centuries.
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