Question 1

How have astronomers searched for evidence of MACHOs in the halo of the Milky Way?

Accepted Answer

A)  They search for stars that are binary companions of MACHOs. 
B)  They search for rapidly moving, massive gas clouds. 
C)  They search for disturbances in the background of gravitational waves. 
D)  They search for stars whose light is briefly amplified by gravitational lensing. 
E)  They search for close binary stars undergoing mass transfer. 
A)  They search for stars that are binary companions of MACHOs. 
B)  They search for rapidly moving, massive gas clouds. 
C)  They search for disturbances in the background of gravitational waves. 
D)  They search for stars whose light is briefly amplified by gravitational lensing. 
E)  They search for close binary stars undergoing mass transfer.

Question 2

In most galaxies, the amount of dark matter and the amount of luminous matter is about equal.

Accepted Answer

A) True 
 B)False

Question 3

What is the connection between active galaxies and galactic mergers?

Accepted Answer

Astronomers believe that galactic merger

Question 4

Elliptical galaxies have the shapes they do because all the stars are orbiting in the same direction in the galaxy.

Accepted Answer

A) True 
 B)False

Question 5

More luminous giant galaxies tend to have __________ supermassive black holes at their centers.

Accepted Answer

A)  more massive 
B)  radio quiet 
C)  more luminous 
D)  slower rotating 
E)  less massive 
A)  more massive 
B)  radio quiet 
C)  more luminous 
D)  slower rotating 
E)  less massive

Question 6

Approximately __________ of spiral galaxies are barred.

Accepted Answer

A)  10 percent 
B)  25 percent 
C)  35 percent 
D)  50 percent 
E)  75 percent 
A)  10 percent 
B)  25 percent 
C)  35 percent 
D)  50 percent 
E)  75 percent

Question 7

If elliptical galaxies do not have cold gas clouds for which we can measure the Doppler shift, then how can we measure the mass of an elliptical galaxy?

Accepted Answer

A)  by measuring the speeds of stars in the nucleus 
B)  by observing the velocity of the hot, X-ray emitting gas that surrounds the galaxy 
C)  by measuring the number of H II regions in the galaxy 
D)  by measuring how many supernovae go off each century 
E)  by measuring the amount of blue light in the galaxy 
A)  by measuring the speeds of stars in the nucleus 
B)  by observing the velocity of the hot, X-ray emitting gas that surrounds the galaxy 
C)  by measuring the number of H II regions in the galaxy 
D)  by measuring how many supernovae go off each century 
E)  by measuring the amount of blue light in the galaxy

Question 8

Active star formation does not occur in elliptical galaxies because they:

Accepted Answer

A)  rotate too fast 
B)  contain little molecular hydrogen 
C)  are too massive 
D)  are too far away 
E)  usually contain active nuclei 
A)  rotate too fast 
B)  contain little molecular hydrogen 
C)  are too massive 
D)  are too far away 
E)  usually contain active nuclei

Question 9

Spiral structure can be triggered in a disk galaxy by:

Accepted Answer

A)  the merger of close binary stars 
B)  a supernova explosion 
C)  the presence of an active nucleus 
D)  the gravity of distant galaxies 
E)  any disturbance to the disk 
A)  the merger of close binary stars 
B)  a supernova explosion 
C)  the presence of an active nucleus 
D)  the gravity of distant galaxies 
E)  any disturbance to the disk

Question 10

Which of the following would NOT be found in an elliptical galaxy?

Accepted Answer

A)  novae 
B)  Type I supernovae 
C)  Type II supernovae 
D)  planetary nebulae 
E)  hot gas 
A)  novae 
B)  Type I supernovae 
C)  Type II supernovae 
D)  planetary nebulae 
E)  hot gas

Question 11

The three-dimensional shape of __________ is set by the average velocities of the stars along each of the three axes.

Accepted Answer

A)  spiral galaxies 
B)  only elliptical galaxies 
C)  spiral bulges 
D)  elliptical galaxies and spiral bulges 
E)  quasars 
A)  spiral galaxies 
B)  only elliptical galaxies 
C)  spiral bulges 
D)  elliptical galaxies and spiral bulges 
E)  quasars

Question 12

A galaxy can contain a supermassive black hole that remains invisible because no matter is falling onto the black hole.

Accepted Answer

A) True 
 B)False

Question 13

If an AGN varies its brightness on a timescale of 4 hours, then what is the size of the AGN measured in AU?

Accepted Answer

The size of the AGN is the distance that

Question 14

Which of these would NOT be useful for measuring the mass of the dark matter halo in a spiral galaxy?

Accepted Answer

A)  H$\alpha$ emission from H II regions in the spiral disk 
B)  the velocities of satellite dwarf galaxies surrounding a spiral galaxy 
C)  absorption lines in the spectra of its globular clusters 
D)  the velocities of star clusters in the outer disk 
E)  all of these can be used to measure the mass of the dark matter 
A)  H$\alpha$ emission from H II regions in the spiral disk 
B)  the velocities of satellite dwarf galaxies surrounding a spiral galaxy 
C)  absorption lines in the spectra of its globular clusters 
D)  the velocities of star clusters in the outer disk 
E)  all of these can be used to measure the mass of the dark matter

Question 15

The Hubble diagram is a way of sorting galaxies by their visual appearance.

Accepted Answer

A) True 
 B)False

Question 16

Elliptical galaxies contain hot gas that is heated by supernova explosions.

Accepted Answer

A) True 
 B)False

Question 17

What is plotted on a rotation curve, and what can it tell us about a galaxy?

Accepted Answer

A rotation curve is a plot of the veloci

Question 18

Galaxies that are classified as quasars were much more numerous in the past.

Accepted Answer

A) True 
 B)False

Question 19

Assume that when a supermassive black hole accretes gas, approximately 50 percent of its mass is converted directly into energy, which is radiated away. If a quasar has a luminosity of 1014 L $\odot$ then what must its mass accretion rate be?

Accepted Answer

A)  1 M $\odot$  per year 
B)  10 M $\odot$ per year 
C)  1 M $\odot$  per century 
D)  10 M $\odot$  per century 
E)  1 M $\odot$  per million years 
A)  1 M $\odot$  per year 
B)  10 M $\odot$ per year 
C)  1 M $\odot$  per century 
D)  10 M $\odot$  per century 
E)  1 M $\odot$  per million years

Question 20

AGNs appear to be powered by:

Accepted Answer

A)  extremely dense star clusters 
B)  supermassive black holes 
C)  ultradense molecular clouds 
D)  decaying dark matter 
E)  supernova explosion 
A)  extremely dense star clusters 
B)  supermassive black holes 
C)  ultradense molecular clouds 
D)  decaying dark matter 
E)  supernova explosion

Exam 20: Galaxies

How have astronomers searched for evidence of MACHOs in the halo of the Milky Way?

In most galaxies, the amount of dark matter and the amount of luminous matter is about equal.

What is the connection between active galaxies and galactic mergers?

Elliptical galaxies have the shapes they do because all the stars are orbiting in the same direction in the galaxy.

More luminous giant galaxies tend to have __________ supermassive black holes at their centers.

Approximately __________ of spiral galaxies are barred.

If elliptical galaxies do not have cold gas clouds for which we can measure the Doppler shift, then how can we measure the mass of an elliptical galaxy?

Active star formation does not occur in elliptical galaxies because they:

Spiral structure can be triggered in a disk galaxy by:

Which of the following would NOT be found in an elliptical galaxy?

The three-dimensional shape of __________ is set by the average velocities of the stars along each of the three axes.

A galaxy can contain a supermassive black hole that remains invisible because no matter is falling onto the black hole.

If an AGN varies its brightness on a timescale of 4 hours, then what is the size of the AGN measured in AU?

Which of these would NOT be useful for measuring the mass of the dark matter halo in a spiral galaxy?

The Hubble diagram is a way of sorting galaxies by their visual appearance.

Elliptical galaxies contain hot gas that is heated by supernova explosions.

What is plotted on a rotation curve, and what can it tell us about a galaxy?

Galaxies that are classified as quasars were much more numerous in the past.

Assume that when a supermassive black hole accretes gas, approximately 50 percent of its mass is converted directly into energy, which is radiated away. If a quasar has a luminosity of 1014 L ⊙\odot⊙ then what must its mass accretion rate be?

AGNs appear to be powered by:

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Assume that when a supermassive black hole accretes gas, approximately 50 percent of its mass is converted directly into energy, which is radiated away. If a quasar has a luminosity of 10¹⁴ L _$\odot$ then what must its mass accretion rate be?