Question 1

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 2

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

Question 3

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

Question 4

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

Accepted Answer

A) True 
 B)False

Question 5

Give three examples of types of active galactic nuclei and give one reason why each is unique.

Accepted Answer

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

Question 6

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

Accepted Answer

A) True 
 B)False

Question 7

The image below was probably taken in ____________ wavelengths because _______________________.

Accepted Answer

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

Question 8

How do we know that many E galaxies contain significant amounts of dark matter?

Accepted Answer

Many E galaxies are observed to contain ...

Question 9

If a galaxy had no dark matter,how would the velocity (v) of a star that orbited far outside the visible extent of the galaxy depend on its distance (r) from the center of the galaxy?

Accepted Answer

A)  ν ∝ r−2
B)  ν ∝ r−1
C)  ν ∝ −2 
B)  ν ∝ r−1 
C)  ν ∝   
D)  ν ∝ r 
E)  ν ∝ r2" class="answers-bank-image d-inline" rel="preload" >
D)  ν ∝ r
E)  ν ∝ r2

Question 10

If the rotational speed of the gas in the disk of a spiral galaxy is 200 km/s at a distance of 25,000 pc from its center,then what is the mass enclosed within this radius?

Accepted Answer

A)  7.5 billion M⨀
B)  18 billion M⨀
C)  70 billion M⨀
D)  230 billion M⨀
E)  400 billion M⨀

Question 11

Approximately __________ of spiral galaxies are barred.

Accepted Answer

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

Question 12

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 13

A galaxy rotation curve is a plot of the rotation speed as a function of the:

Accepted Answer

A)  galaxy's luminosity
B)  mass of the dark matter halo
C)  brightness of the luminous matter in the galaxy
D)  radius from the center
E)  ages of star clusters

Question 14

What determines the three-dimensional shapes of galaxies?

Accepted Answer

The velocities of st...

Question 15

We interpret the fact that we saw more AGNs in the past than we do today to indicate that:

Accepted Answer

A)  there were fewer galaxy-galaxy interactions in the past
B)  there were more galaxy-galaxy interactions in the past
C)  supermassive black holes were larger in the past
D)  today's AGNs are primarily hidden by large amounts of cold gas and dust
E)  AGNs had bigger central black holes in the past

Question 16

What happens to active galaxies when their AGNs run out of fuel?

Accepted Answer

A)  The black holes powering them collapse even further.
B)  They simply become normal galaxies.
C)  They slowly dissipate into clouds of gas and dust.
D)  They eventually pull in material from farther out,starting the AGN process all over again.
E)  They explode as gamma-ray bursts.

Question 17

The disks of spiral galaxies appear blue because:

Accepted Answer

A)  they are moving toward us
B)  they contain a relatively high concentration of low-mass stars
C)  they contain active regions of star formation
D)  they contain more metals that,when ionized,emit blue light
E)  stars collide with each other frequently in these dense regions and explode as Type I supernovae

Question 18

Stars in the disks of spiral galaxies have orbits that:

Accepted Answer

A)  are randomly oriented
B)  constantly are getting larger
C)  mostly aligned in the same plane
D)  spiral shaped
E)  unaffected by dark matter

Question 19

The unified model of AGN suggests that quasars,Seyfert galaxies,and radio galaxies:

Accepted Answer

A)  are unrelated,although they are all very luminous galaxies at radio wavelengths
B)  are powered by similar mass accretion rates onto supermassive black holes
C)  are driven by violent mergers of two gas-rich spiral galaxies
D)  are similar phenomena but viewed from different orientation angles
E)  are all powered by high rates of star formation and supernova explosions

Question 20

The type of AGN we see depends mostly on the angle at which we view the galaxy.

Accepted Answer

A) True 
 B)False

Exam 20: Galaxies

A galaxy rotation curve is a plot of the rotation speed as a function of the:

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

What determines the three-dimensional shapes of galaxies?

Correct AnswerverifiedThe velocities of st...View AnswerShow Answer

The unified model of AGN suggests that quasars,Seyfert galaxies,and radio galaxies:

Correct AnswerverifiedShow Answer

Stars in the disks of spiral galaxies have orbits that:

Correct AnswerverifiedShow Answer

How do we know that many E galaxies contain significant amounts of dark matter?

Correct AnswerverifiedMany E galaxies are observed to contain ...View AnswerShow Answer

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

Correct AnswerverifiedShow Answer

If the rotational speed of the gas in the disk of a spiral galaxy is 200 km/s at a distance of 25,000 pc from its center,then what is the mass enclosed within this radius?

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedThe size of the AGN is the distance that...View AnswerShow Answer

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?

Correct AnswerverifiedShow Answer

The type of AGN we see depends mostly on the angle at which we view the galaxy.

Correct AnswerverifiedShow Answer

If a galaxy had no dark matter,how would the velocity (v) of a star that orbited far outside the visible extent of the galaxy depend on its distance (r) from the center of the galaxy?

Correct AnswerverifiedShow Answer

The disks of spiral galaxies appear blue because:

Correct AnswerverifiedShow Answer

Approximately __________ of spiral galaxies are barred.

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

Give three examples of types of active galactic nuclei and give one reason why each is unique.

Correct AnswerverifiedThree types of AGNs: (1)quasars-extremel...View AnswerShow Answer

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

Correct AnswerverifiedA rotation curve is a plot of the veloci...View AnswerShow Answer

The image below was probably taken in ____________ wavelengths because _______________________.

Correct AnswerverifiedShow Answer

We interpret the fact that we saw more AGNs in the past than we do today to indicate that:

Correct AnswerverifiedShow Answer

What happens to active galaxies when their AGNs run out of fuel?

Correct AnswerverifiedShow Answer

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The velocities of st...
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Many E galaxies are observed to contain ...
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The size of the AGN is the distance that...
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Three types of AGNs: (1)quasars-extremel...
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A rotation curve is a plot of the veloci...
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The image below was probably taken in wavelengths because ___________.

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