A) Pulsars have the same upper mass limit as neutron stars do.
B) Telescopic images of pulsars and neutron stars look exactly the same.
C) No massive object, other than a neutron star, could spin as fast as we observe pulsars to spin and remain intact.
D) We have observed massive- star supernovae produce pulsars.
E) This is only a theory that has not yet been confirmed by observations.
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A) The compact object may be either a neutron star or a black hole.
B) The radiation from an accretion disk may vary rapidly in time.
C) The accretion disk consists of material that spills off the companion star.
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) X- rays are emitted by the hot gas in the accretion disk.
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A) a white dwarf that gains enough mass to exceed the 1.4- solar- mass limit
B) hydrogen fusion on the surface of a neutron star
C) hydrogen fusion on the surface of a white dwarf
D) carbon fusion in the core of a white dwarf
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A) as much as an average person
B) as much as the entire Earth
C) as much as a truck
D) about 5 pounds
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A) As gravity overwhelms the neutron degeneracy pressure, it will explode as a supernova.
B) It will spin ever slower, the magnetic field will weaken, and it will become invisible.
C) It will spin ever faster, becoming a millisecond pulsar.
D) As gravity overwhelms the neutron degeneracy pressure, it will become a white dwarf.
E) The neutron degeneracy pressure will eventually overwhelm gravity and the pulsar will slowly evaporate.
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A) a star that slowly changes its brightness, getting dimmer and then brighter, with a period of anywhere from a few hours to a few weeks
B) an object that emits flashes of light several times per second (or even faster) , with near perfect regularity
C) a star that changes color rapidly, from blue to red and back again
D) an object that emits random "pulses" of light, sometimes with only a fraction of a second between pulses and other times with several days between pulses
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A) Cygnus X- 1 is a powerful X- ray burster, so it must contain a black hole.
B) The fact that we see strong X- ray emission tells us that the system must contain a black hole.
C) No light is emitted from this star system, so it must contain a black hole.
D) It emits X- rays characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star.
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A) bright X- ray emission that varies on a time scale of a few hours
B) intense X- ray bursts
C) visible and ultraviolet light from the companion star
D) spectral lines from the companion star that alternately shift to shorter and longer wavelengths
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A) It rotates 30 times per second.
B) It's a mystery; no one really knows.
C) It is eclipsed by a companion 30 times per second.
D) A jet ejects energy and particles from a hot spot 30 times per second.
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A) Their immediate ancestors were chimpanzees.
B) They evolved on a different planet in a different star system, and moved to their current location.
C) They evolved from primitive wormlike creatures that had 13 legs, 4 eyes, and bald heads, thus explaining why such critters are now considered a spectacular delicacy.
D) As a result of traumatic experiences to their evolutionary ancestors, they dislike television.
E) They believe that the presence of two stars in their system was critical to their evolution.
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A) only the mass of the black hole
B) both the mass and chemical composition of the black hole
C) the way in which the black hole formed
D) the observationally measured radius of the black hole
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A) The white dwarf will collapse to become a black hole.
B) The white dwarf will explode completely as a white dwarf supernova.
C) The white dwarf will collapse in size, becoming a neutron star.
D) The white dwarf will undergo a nova explosion.
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A) The gas in the inner parts of the disk is hotter than the gas in the outer parts of the disk.
B) Accretion disks are made primarily of hydrogen and helium gas.
C) The gas in the inner parts of the disk travels faster than the gas in the outer parts of the disk.
D) The primary factor determining whether a white dwarf has an accretion disk is the white dwarf's mass.
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