Exam 21: Galaxy Evolution

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A) 3 solar masses.
B) 10 solar masses.
C) 1 trillion solar masses.
D) 1 billion solar masses.

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A) Supermassive black holes existed only when the universe was young and no longer exist today.
B) Active galactic nuclei tend to become less active as they age.
C) Active galactic nuclei can form only at large distances from the Milky Way.
D) The jets seen in many active galactic nuclei must cause them to move far away from us.

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A) is always determined by the angular momentum of the protogalactic cloud that formed it.
B) may either be the result of conditions in the protogalactic cloud that formed it or the result of later interactions with other galaxies.
C) is determined by whether the galaxy is located in a cluster where collisions are likely or outside a cluster where collisions are less likely.
D) may either be a result of the mass of the protogalactic cloud that formed it or the result of the heavy element abundance in that cloud.

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A) elliptical galaxies
B) spiral galaxies
C) irregular galaxies
D) We can't say,because we are living at a time when the universe is 14 billion years old,not 2 billion years.

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A) Observed radiation from the galactic center varies significantly in brightness in times as short as a few days.
B) Infrared observations show that many stars are forming near the centers of active galaxies.
C) Radio observations sometimes show long jets of material extending millions of light-years out from the galactic center.
D) The total amount of radiation coming from the galactic center is,in some cases,comparable to the amount of radiation put out by 10 billion or more ordinary stars.
E) Spectral lines from the galactic center indicate that clouds of gas are orbiting a central object at very high speed.

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A) Observations at different distances show galaxies of different ages and therefore different stages of evolution.
B) We can observe the birth of galaxies.
C) We can observe the evolution of a single galaxy over time.
D) We can observe two galaxies merging and what the result is,helping us learn how mergers affect evolution.
E) We can see what our galaxy used to look like and therefore theorize about the physical processes that led to its current appearance.

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Galaxies are much closer together,relati...

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A) light emitted by hot gas in an accretion disk that swirls around the black hole.
B) intense radiation emitted by the black hole itself.
C) the combined light of thousands of young,high-mass stars that orbit the black hole.
D) radio waves emitted from radio lobes found on either side of the galaxy we see in visible light.

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A) Elliptical galaxies are denser than spiral galaxies.
B) Elliptical galaxies are generally larger than spiral galaxies.
C) Elliptical galaxies at high redshifts lack young,blue stars.
D) Elliptical galaxies have more gas than spiral galaxies.
E) Elliptical galaxies have denser stars than spiral galaxies.

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A) Galaxies were closer together in the past because the universe was smaller.
B) Galaxies were more active in the past and therefore would have collided with each other more frequently.
C) Galaxies were much bigger in the past since they had not contracted completely.
D) Galaxies attracted each other more strongly in the past because they were more massive;they had not yet turned most of their mass into stars.

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A) observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies
B) the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies
C) observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy
D) observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies
E) all of the above

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A) nuclear fusion in the accretion disk surrounding the black hole.
B) gravitational potential energy released by matter that is falling toward the black hole.
C) matter-antimatter annihilation occurring just outside the event horizon of the black hole.
D) jets emerging from the accretion disk.

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A) We now have images and spectra that show quasars to be embedded at the centers of distant galaxies and within distant galaxy clusters.
B) All quasars have large redshifts.
C) Now that we can explain bright quasar emission with power due to the presence of supermassive black holes,there is no reason to doubt that quasars are far away.
D) No one could think of a way to explain quasar speeds if they are nearby,so we concluded they must be far away.

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A) the mass of the halo and disk of the host galaxy is also very large.
B) the host galaxy is eventually completely consumed by the black hole.
C) the galaxy is always a spiral galaxy.
D) the mass of the bulge of the host galaxy is also very large.

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A) 10 cm.
B) 3 m.
C) 30 m.
D) 1 km.
E) 100 km.

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