A) a galaxy with a supermassive black hole at the center
B) an older name for an active galaxy
C) a galaxy that looks like it is exploding
D) an active galaxy with large radiation output at many different wavelengths across the spectrum
F) C) and D)
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A) red supergiant star
B) center of the Milky Way Galaxy
C) quasar
D) supernova explosion in a neighboring galaxy
F) All of the above
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A) because they are among the most massive objects known
B) because they are all so far away
C) because their radiation is narrowly confined to particular regions of the spectrum
D) because astronomers can observe most quasars up off the galactic plane where they are not obscured by gas and dust
F) A) and C)
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A) are more common in nearby clusters of galaxies and less common in distant clusters of galaxies.
B) are rare in the Local Group, with only one or two examples.
C) increase in number as redshift increases, a relationship that persists to the highest redshifts astronomers can measure.
D) peaked in number about 2 billion years after the Big Bang.
F) B) and C)
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A) very high recession speeds of the sources away from the Milky Way Galaxy.
B) absorption of all but the red parts of the quasar spectrum by intergalactic matter.
C) Zeeman effects from the very intense magnetic fields in the vicinity of the source.
D) high gravitational fields at the surfaces of the quasars (gravitational redshift) .
F) B) and D)
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A) exploding shell of a supernova
B) black hole
C) quasar
D) pulsar
F) A) and D)
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A) sources of great energy, very large in actual size, and shaped like galaxies.
B) sources of intense radio energy only, not visible at other wavelengths, and relatively large but very distant.
C) prolific sources of energy, starlike in appearance, and intrinsically small.
D) starlike sources of great energy located in the Milky Way Galaxy and intrinsically very small.
F) All of the above
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A) 3000 km/s, or about 1% the speed of light.
B) more than 99% the speed of light.
C) about 10% the speed of light.
D) almost half the speed of light.
F) A) and D)
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A) by measuring the object's mass and using a reasonable value for the average density for matter to calculate its volume and hence its diameter
B) by using radio interferometry because this technique can resolve far greater detail than optical imaging
C) by measuring brightness variability because an object cannot vary more rapidly than the time taken for light to cross the source
D) by measuring the redshift of its spectrum because the redshift will depend on the source size
F) All of the above
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A) 3.2 * 107 L
B) 6.3 * 109 L
C) 1.9 *1011 L
D) 5.3*1012 L
F) None of the above
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A) only about 1/10 of the Galaxy's output but from a small volume of space
B) 100 times brighter
C) about a million times brighter
D) about the same energy output
F) C) and D)
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A) the redshift of its radio wavelength signal was as high as anything measured up to that time.
B) it was first discovered at X-ray wavelengths and detected at optical and radio wavelengths only some time later.
C) it was so bright at optical wavelengths that no one expected it to be a galaxy.
D) it was very faint at visible wavelengths but extremely bright at radio wavelengths.
F) A) and B)
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A) 100 million
B) 800 million
C) 3.2 billion
D) 12.1 billion
F) A) and B)
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A) stars falling into a supermassive black hole, then their remnants being thrown out in all directions.
B) supernova explosions in an extremely dense star cluster at the center of the galaxy.
C) the violent merger of two galaxies in which the collision throws out jets of matter along the rotation axis of the larger galaxy.
D) a supermassive black hole at the center of an accretion disk and material being projected out perpendicular to the disk in both directions.
F) B) and D)
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A) strong, highly redshifted emission lines.
B) doubled emission lines split by the Doppler shift from oppositely directed jets of material.
C) absorption lines of highly ionized atoms.
D) A fairly smooth continuum with exceptionally weak spectral lines.
F) B) and C)
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A) The discovery is not really a surprise because all quasars are formed by the same processes and all have virtually identical spectra.
B) The two quasars are part of a binary pair of quasars that were formed together, are at the same stage in their lives, and have the same spectra.
C) The two quasars cannot be gravitational lensing images because there is no visible lensing object in the space between them.
D) The two quasars are most likely gravitational lensing images, and the lensing object is mostly dark matter with little visible emission.
F) A) and B)
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A) 7 billion years
B) 9 billion years
C) 11 billion years
D) 13 billion years
F) B) and D)
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A) two very hot gas clouds, suspended by magnetic fields above the rotation axis of a galaxy, emitting 21-cm radio waves.
B) a radio source split by a dark absorbing disk across its center as seen from Earth.
C) the double image of a single source behind the galaxy produced by gravitational lensing by the galaxy.
D) two oppositely directed jets of energetic particles that collide with intergalactic gas.
F) A) and B)
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