Exam 20: Galaxies

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A) Quasars and Seyfert galaxies are stellar-like sources.
B) Their brightness varies by factors of a few.
C) The emission lines in their spectra show gas rotating at speeds of thousands of km/s.
D) Their brightness varies on timescales ranging from hours to a day.
E) We can measure their angular size, which gives us the physical size when we know the distance.

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A) They are very far away.
B) They are moving away from us.
C) They have rapid internal motions.
D) They are very dense.
E) They have few heavy elements.

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The radius of the gas is:
r=26,000 ly = ...

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A) rotates at the same speed as the gas in the disk
B) rotates at a speed that is different than the gas in the disk
C) stays constant in time as the gas in disk rotates through it
D) rotates backward compared to the stellar orbits
E) must only last a short time, since few galaxies with disks show spiral patterns

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A) change constantly
B) are very large in size
C) are equal in all directions
D) are constant in time
E) are orientated in random in directions

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A) tightness of the spiral arms
B) luminosity of the galaxy
C) age of the galaxy
D) thickness of the disk
E) presence of an active nucleus

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A) radio; the disk probably contains many planets with intelligent life, who are beaming out radio and television signals into space
B) infrared; the central regions are bright, and cool stars in the bulges emit a lot of infrared light
C) visible; there is a lot dust in this galaxy that blocks light in a ring about halfway along the disk
D) ultraviolet; the light from hot young stars is mainly found along spiral arms
E) X-ray; the central nucleus is easily seen, and AGN emit a lot of X-rays

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Three types of AGNs: (1) quasars-extreme...

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All AGN of any luminosity cons...

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A) 1 * 10¹¹ M _$\odot$
B) 2 * 10¹¹ M _$\odot$
C) 8 *10¹¹ M _$\odot$
D) 1 * 10¹² M _$\odot$
E) 4 * 10¹² M _$\odot$

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A) 5 percent
B) 25 percent
C) 33 percent
D) 50 percent
E) 90 percent

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A) We know that massive stars make black holes, and most galaxies contain a lot of massive stars.
B) We know black holes are made of dark matter, and galaxies are mostly made up of dark matter.
C) We know that black holes emit radio waves, and many AGNs are bright at radio waves.
D) We measure that the mass of the black hole is increasing as material falls into it.
E) In some systems, we can see both redshifted and blueshifted emission lines from material orbiting around the black hole.

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A) the spiral merges with another galaxy
B) the galaxy is young
C) the galaxy's disk is regularly disturbed
D) the galaxy absorbs a satellite galaxy
E) a supernova explosion takes place

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