1. © 2017 Pearson Education, Inc.

2. Question 1
Based on galactic rotation curves and motions in clusters of galaxies, dark matter
makes up about 90 percent of the matter in the universe.
is best detected by the largest optical telescopes.
makes up about 10 percent of the matter in clusters of galaxies.
exists but has no observable effects on galaxies.
is the result of gas and dust.
Answer: a
© 2017 Pearson Education, Inc.

3. Question 1
Based on galactic rotation curves and motions in clusters of galaxies, dark matter
makes up about 90 percent of the matter in the universe.
is best detected by the largest optical telescopes.
makes up about 10 percent of the matter in clusters of galaxies.
exists but has no observable effects on galaxies.
is the result of gas and dust.
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4. Question 2 Collisions between galaxies
are much rarer than collisions between stars.
can transform elliptical galaxies into spirals.
trigger Type II supernova explosions in the halo.
cause gas and dust clouds to collide, leading to rapid star formation.
Answer: d
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5. Question 2 Collisions between galaxies
are much rarer than collisions between stars.
can transform elliptical galaxies into spirals.
trigger Type II supernova explosions in the halo.
cause gas and dust clouds to collide, leading to rapid star formation.
Explanation: Galaxies are relatively close compared with their size. In clusters of galaxies, collisions clearly occur.
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6. Question 3
When spiral galaxies collide, the greatest impact occurs on their
globular cluster stars.
giant molecular clouds.
central bulge stars.
open clusters.
disk stars.
Answer: b
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7. Question 3
When spiral galaxies collide, the greatest impact occurs on their
globular cluster stars.
giant molecular clouds.
central bulge stars.
open clusters.
disk stars.
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8. Question 4
Due to the density and collisions among galaxies, _____ are rare in the centers of clusters.
giant ellipticals
irregulars
spirals
active galaxies
radio galaxies
Answer: c
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9. Question 4
Due to the density and collisions among galaxies, _____ are rare in the centers of clusters.
giant ellipticals
irregulars
spirals
active galaxies
radio galaxies
Explanation: The gas, dust, and disks of spiral galaxies are tidally disrupted, and even destroyed, in the centers of dense clusters, which are often dominated by giant elliptical galaxies.
© 2017 Pearson Education, Inc.

10. Question 5 The rapid variation of brightness of quasars indicates
the source of energy is very small.
energy is coming from matter and antimatter.
the energy source is rotating rapidly.
a chain reaction of supernovas occurs.
there are many separate sources of energy in the core.
Answer: a
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11. Question 5 The rapid variation of brightness of quasars indicates
the source of energy is very small.
energy is coming from matter and antimatter.
the energy source is rotating rapidly.
a chain reaction of supernovas occurs.
there are many separate sources of energy in the core.
Explanation: The size of an object cannot be larger than the distance light can travel in the time it takes to change its brightness.
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12. Question 6
A galaxy seen 1 billion light-years away means we see it as it
was when the universe was 1 billion years old.
will be 1 billion years from now.
was 1 billion years ago.
is today, but redshifted 10 percent of the speed of light.
was just after the Big Bang.
Answer: c
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13. Question 6
A galaxy seen 1 billion light-years away means we see it as it
was when the universe was 1 billion years old.
will be 1 billion years from now.
was 1 billion years ago.
is today, but redshifted 10 percent of the speed of light.
was just after the Big Bang.
Explanation: Looking farther away in space means looking back further in time, to when the object (and universe) was younger.
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14. Question 7
The large-scale distribution of galaxies in the universe reveals
a smooth, continuous, and homogeneous arrangement of clusters.
large voids, with most of the galaxies lying in filaments and sheets.
a large supercluster at the center of the universe.
a central void with walls of galaxies at the edge of the universe.
Answer: b
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15. Question 7
The large-scale distribution of galaxies in the universe reveals
a smooth, continuous, and homogeneous arrangement of clusters.
large voids, with most of the galaxies lying in filaments and sheets.
a large supercluster at the center of the universe.
a central void with walls of galaxies at the edge of the universe.
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16. Question 8
The lensing of a distant quasar is produced in a foreground galaxy by its
total mass of stars, gas, and dark matter.
central supermassive black hole.
globular clusters.
magnetic fields.
intergalactic gas.
Answer: a
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17. Question 8
The lensing of a distant quasar is produced in a foreground galaxy by its
total mass of stars, gas, and dark matter.
central supermassive black hole.
globular clusters.
magnetic fields.
intergalactic gas.
Explanation: The twin quasar AC114 has two images of the same object.
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18. Question 9 The blue arcs in this image are emission nebulae.
nearby blue dwarf galaxies.
blue supergiant stars.
a very distant galaxy imaged by a massive galaxy cluster between us and the distant galaxy.
Answer: d
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19. Question 9 The blue arcs in this image are emission nebulae.
nearby blue dwarf galaxies.
blue supergiant stars.
a very distant galaxy imaged by a massive galaxy cluster between us and the distant galaxy.
Explanation: The nearby galaxy—yellow blobs in the center of this image—is 1.5 billion pc from us. The blue arcs are all images of a single, much more distant galaxy.
© 2017 Pearson Education, Inc.