Question 1

What makes up the majority of the mass of an individual spiral galaxy?

Accepted Answer

A)   A central supermassive black hole
B)   Dark matter
C)   Massive O- and B-type stars
D)   Cold molecular gas clouds B

Question 2

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

Question 3

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 B

Question 4

Approximately __________ of spiral galaxies are barred.

Accepted Answer

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

Question 5

Why do rotation curves of galaxies imply that dark matter exists?

Accepted Answer

A)   The velocity of stars rises dramatically at large distances from the centers of galaxies,implying large amounts of dark matter cause these stars to move much faster than stars at smaller distances.
B)   The velocity of stars stays somewhat constant at distances beyond the visible edges of galaxies,implying that more matter than what we observe in stars and gas must be there.
C)   The velocity of stars is low in the inner regions of galaxies,suggesting that dark matter is impeding their motion.
D)   The velocity of stars rises quickly in the inner regions of galaxies,suggesting that unseen matter is gravitationally moving this material at faster rates than expected.

Question 6

The 3-dimensional shape of __________ is set by the average velocities of the stars along each of the three axes.

Accepted Answer

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

Question 7

Spiral structure:

Accepted Answer

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 the disk rotates through it
D)   none of the above is true

Question 8

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

Question 9

Why is our own galaxy not an active galaxy today?

Accepted Answer

Because there curren...

Question 10

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 11

Which of the given rotation curves in the figure below represents what astronomers would expect if dark matter exists in the halo of a spiral galaxy?

Accepted Answer

A)   Rotation curve A
B)   Rotation curve B
C)   Rotation curve C
D)   None of the curves would be correct.

Question 12

Astronomers believe that all giant galaxies probably contain supermassive black holes.

Accepted Answer

A) True 
 B)False

Question 13

In some radio galaxies,we only see one side of the jet because:

Accepted Answer

A)   the black hole only produces a jet in one direction
B)   of relativistic beaming
C)   the other side is inside the black hole's event horizon
D)   of dust obscuration

Question 14

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.

Question 15

The figure below shows the unified model of AGNs along with three observers.Which observer would likely not be able to see the accretion disk?

Accepted Answer

A)   Observer A
B)   Observer B
C)   Observer C
D)   All observers can equally see detail in the object.

Question 16

What could you use to measure the mass of the dark matter halo in a spiral galaxy?

Accepted Answer

A)   Hydrogen 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)   all of the above D

Question 17

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)   v  ∝\propto∝  r-1/2
B)   v  ∝\propto∝  r2
C)   v  ∝\propto∝  r-1
D)   v  ∝\propto∝  r

Question 18

If the rotational speed of the gas in the disk of a spiral galaxy is 100 km/s at a distance of 26,000 light-years from its center,then what is the mass enclosed within this radius? If the mass of luminous matter inside this radius is 5 billion M$\odot$  then what fraction of the galaxy's mass is made of dark matter?

Accepted Answer

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

Question 19

Why is 21-cm radiation a good spiral arm tracer?

Accepted Answer

A)   Emitted by neutral hydrogen,it traces the location of concentrations of gas.
B)   Emitted by O and B stars,it traces the location of newly formed stars.
C)   Emitted by ionized hydrogen,it traces the location of H II regions.
D)   Emitted by molecular hydrogen,it traces the location of clouds in the process of collapsing into stars.

Question 20

We know that spiral galaxies contain dark matter because the gas in the disk rotates with a velocity that decreases in a way that is similar to our Solar System.

Accepted Answer

A) True 
 B)False

Exam 15: The Realm of the Galaxies

What makes up the majority of the mass of an individual spiral galaxy?

Correct Answer
verified
B

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

Correct Answer
verified

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

Correct Answer
verified
B

Approximately __________ of spiral galaxies are barred.

Correct Answer
verified

Why do rotation curves of galaxies imply that dark matter exists?

Correct Answer
verified

The 3-dimensional shape of __________ is set by the average velocities of the stars along each of the three axes.

Correct Answer
verified

Spiral structure:

Correct Answer
verified

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

Correct Answer
verified

Why is our own galaxy not an active galaxy today?

Correct Answer
verified
Because there curren...
View 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 Answer
verified
The size of the AGN is the distance that...
View Answer

Which of the given rotation curves in the figure below represents what astronomers would expect if dark matter exists in the halo of a spiral galaxy?

Correct Answer
verified

Astronomers believe that all giant galaxies probably contain supermassive black holes.

Correct Answer
verified

In some radio galaxies,we only see one side of the jet because:

Correct Answer
verified

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

Correct Answer
verified

The figure below shows the unified model of AGNs along with three observers.Which observer would likely not be able to see the accretion disk?

Correct Answer
verified

What could you use to measure the mass of the dark matter halo in a spiral galaxy?

Correct Answer
verified
D

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 Answer
verified

Correct Answer
verified
The radius of the gas is r = 26,000 ly =...
View Answer

Why is 21-cm radiation a good spiral arm tracer?

Correct Answer
verified

We know that spiral galaxies contain dark matter because the gas in the disk rotates with a velocity that decreases in a way that is similar to our Solar System.

Correct Answer
verified

Exam 15: The Realm of the Galaxies

What makes up the majority of the mass of an individual spiral galaxy?

Correct AnswerverifiedB

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

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedB

Approximately __________ of spiral galaxies are barred.

Correct AnswerverifiedShow Answer

Why do rotation curves of galaxies imply that dark matter exists?

Correct AnswerverifiedShow Answer

The 3-dimensional shape of __________ is set by the average velocities of the stars along each of the three axes.

Correct AnswerverifiedShow Answer

Spiral structure:

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

Why is our own galaxy not an active galaxy today?

Correct AnswerverifiedBecause there curren...View AnswerShow 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

Which of the given rotation curves in the figure below represents what astronomers would expect if dark matter exists in the halo of a spiral galaxy?

Correct AnswerverifiedShow Answer

Astronomers believe that all giant galaxies probably contain supermassive black holes.

Correct AnswerverifiedShow Answer

In some radio galaxies,we only see one side of the jet because:

Correct AnswerverifiedShow Answer

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

Correct AnswerverifiedShow Answer

The figure below shows the unified model of AGNs along with three observers.Which observer would likely not be able to see the accretion disk?

Correct AnswerverifiedShow Answer

What could you use to measure the mass of the dark matter halo in a spiral galaxy?

Correct AnswerverifiedD

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

Correct AnswerverifiedThe radius of the gas is r = 26,000 ly =...View AnswerShow Answer

Why is 21-cm radiation a good spiral arm tracer?

Correct AnswerverifiedShow Answer

We know that spiral galaxies contain dark matter because the gas in the disk rotates with a velocity that decreases in a way that is similar to our Solar System.

Correct AnswerverifiedShow Answer

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B

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B

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Because there curren...
View Answer

Correct Answer
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The size of the AGN is the distance that...
View Answer

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Correct Answer
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D

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

Correct Answer
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Correct Answer
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