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A) The higher density of gas has a stronger force of gravity,and therefore the cloud collapses more quickly.
B) The force of gravity can pull the material into a more spherical shape.
C) The more frequent collisions between particles randomize the particle orbits.
D) The thickness of the dense cloud prevents a disk from forming.
E) The higher gas density forms stars more efficiently,so all the gas is converted into stars before a disk can form.
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A) The beginning of the universe is modeled after a supernova explosion,and all the elements were produced in the proper quantities by the star.
B) Hydrogen and helium filled all of space,and certain regions of the universe were slightly denser than others.
C) Hydrogen and helium filled all of space,and all the universe was exactly the same density.
D) The universe has always been expanding,and denser areas contracted to form the first stars.
E) The universe was composed originally only of hydrogen,and all the other elements came from stars.
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A) Relative to their sizes,galaxies are closer together than stars.
B) Galaxies are much larger than stars.
C) Galaxies travel through space much faster than stars.
D) Galaxies have higher redshifts than stars.
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A) The observed features that cause us to classify it as a "starburst" must be only temporary phenomena in the galaxy's history.
B) Its rate of star formation is many times higher than the rate of star formation in the Milky Way.
C) Supernovae occur so frequently that their effects combine to drive a galactic wind that blows material into intergalactic space.
D) The observed features of the starburst are thought to be caused by the presence of a supermassive black hole in the galaxy's center.
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A) quasars
B) the radio emission from radio galaxies
C) the huge jets seen emerging from the centers of some galaxies
D) the large sizes of central dominant galaxies
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A) an irregular galaxy.
B) an elliptical galaxy.
C) a spiral galaxy.
D) a torn and incoherent galaxy.
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Jets in radio galaxies and in protostars...View Answer
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A) They're found in clusters of galaxies.
B) They are often spiral galaxies.
C) They often have multiple galactic nuclei near their centers.
D) They are thought to form by the merger of several smaller galaxies.
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