Question 1

Most large galaxies in the universe are

Accepted Answer

A)   elliptical.
B)   spiral or lenticular.
C)   irregular.
D)   abnormal.E) A) and B)
F) None of the above

Question 2

Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars?

Accepted Answer

A)   It is an extremely bright star cluster.
B)   It is close enough to us that the distance to its stars can be found by stellar parallax.
C)   It is an old globular cluster whose age we can determine very accurately by measuring its main-sequence turn-off point.
D)   It's a cluster that has been photographed over many decades, so we know how the stars vary in brightness.
E)   It contains many Cepheid variable stars that can be used to determine its distance.F) B) and C)
G) A) and E)

Question 3

Which of the following types of galaxies have a disk and spheroidal component but lack spiral arms?

Accepted Answer

A)   ellipticals
B)   lenticulars
C)   irregulars
D)   all of the aboveE) B) and C)
F) All of the above

Question 4

Does Hubble's law work well for galaxies in the Local Group? Why or why not?

Accepted Answer

A)   No, because galaxies in the Local Group are gravitationally bound together.
B)   No, because Hubble did not know the Local Group existed when he discovered his law.
C)   No, because we do not know the precise value of Hubble's constant.
D)   Yes, it works so well that we have never detected any measurable deviations from its predictions.E) A) and C)
F) B) and D)

Question 5

How does a starburst end? What might happen to the galaxy afterwards?

Accepted Answer

A starburst might end by simply using up...

Question 6

Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What can we learn from this observation?

Accepted Answer

A)   We can learn the distance to the galaxy.
B)   It will allow us to calculate the rotation rate of the galaxy.
C)   It will allow us to determine the mass of the galaxy.
D)   Under the rules of the International Astronomical Union, we will be entitled to naming rights for the galaxy.E) All of the above
F) A) and D)

Question 7

What is the most accurate way to determine the distance to a nearby star?

Accepted Answer

A)   radar ranging
B)   stellar parallax
C)   main-sequence fitting
D)   Cepheid variables
E)   Hubble's lawF) A) and E)
G) D) and E)

Question 8

Suppose that Hubble's constant were 20 kilometers per second per million light-years. How fast would we expect a galaxy 100 million light-years away to be moving? (Assume the motion is due only to Hubble's law.)

Accepted Answer

A)   away from us at 2,000 km/s
B)   away from us at 200 km/s
C)   toward us at 2,000 km/s
D)   away from us at 20,000 km/sE) A) and D)
F) A) and C)

Question 9

Why does the merger of two spiral galaxies often trigger starbursts?

Accepted Answer

The dusty molecular clouds in spiral gal...

Question 10

Quasars radiate most of their energy as radio emission.

Accepted Answer

A) True 
 B)False

Question 11

What is Hubble's law?

Accepted Answer

A)   The luminosity of the Cepheid variable star is directly proportional to its pulsation period.
B)   The recession velocity of a galaxy is directly proportional to its distance.
C)   The recession velocity of a galaxy is inversely proportional to its distance.
D)   The faster a spiral galaxy's rotation speed, the more luminous it is.
E)   The faster a spiral galaxy's rotation speed, the less luminous it is.F) A) and E)
G) A) and D)

Question 12

Why can't we see past the cosmological horizon?

Accepted Answer

A)   The universe extends only to this horizon.
B)   Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
C)   We do not have telescopes big enough.
D)   We do not have detectors sensitive enough.
E)   The cosmological horizon is infinitely far away, and we can't see to infinity.F) C) and D)
G) C) and E)

Question 13

Recall that Hubble's law is written v = H₀d, where v is the recession velocity of a galaxy located a distance d away from us, and H₀ is Hubble's constant. Suppose H₀ = 20 km/s/Mly. How fast would a galaxy located 1375 Mly distant be receding from us? Show all work clearly, and state your final answer with a complete sentence. Give the speed both in units of kilometers per second and as a percentage of the speed of light.
v = H₀d = (1375 Mly)
 $ \left[20 \frac{\mathrm{km} / \mathrm{s}}{\mathrm{Mly}}\right] $
= 27,500
 $ \frac{\mathrm{km}}{\mathrm{s}} $
= 0.09c

Accepted Answer

The galaxy is recedi...

Question 14

A protogalactic cloud with slow star formation is more likely to form a spiral galaxy than an elliptical galaxy.

Accepted Answer

A) True 
 B)False

Question 15

One possible explanation for a galaxy's type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed due to other interactions, we'd expect this galaxy to be ________.

Accepted Answer

A)   an irregular galaxy
B)   an elliptical galaxy
C)   a spiral galaxy
D)   a torn and incoherent galaxyE) A) and B)
F) A) and D)

Question 16

Which of the following is not one of the three major categories of galaxies?

Accepted Answer

A)   Globular galaxies
B)   Elliptical galaxies
C)   Spiral galaxies
D)   Irregular galaxiesE) None of the above
F) A) and D)

Question 17

Use the graph above showing data for the brightest galaxies in clusters of galaxies to answer the following question. If new studies show that the exceptions are a class of galaxies with extraordinarily bright centers, which conclusion is NOT justified based on the plot and the findings of these new studies?

Accepted Answer

A)   Bright nuclei are caused by supermassive black holes surrounded by hot gas.
B)   Galaxies appear redder the farther away they are.
C)   Bright nuclei are more common in cluster galaxies that are farther away.
D)   Bright nuclei were more common long ago, since the light from more distant galaxies has been traveling much longer.E) B) and D)
F) B) and C)

Question 18

Suppose we observe a source of X-rays that varies substantially in brightness over a period of a few days. What can we conclude?

Accepted Answer

A)   The X-ray source must be a quasar.
B)   The X-ray source must contain a black hole with an accretion disk.
C)   The X-ray source can be no more than a few light-days in diameter.
D)   The X-ray source must have a strong, rapidly varying magnetic field.
E)   We must seeing the rapid orbit of two stars in a binary system.F) A) and C)
G) B) and E)

Question 19

How are jets thought to be produced by active galaxies?

Accepted Answer

Magnetic fields in the accreti...

Question 20

Collisions between galaxies typically unfold over a period of ________.

Accepted Answer

A)   several days
B)   several months
C)   thousands of years
D)   hundreds of millions of yearsE) B) and C)
F) A) and B)

Exam 15: Galaxies and the Foundation of Modern Cosmology

Correct Answer
verified

Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What can we learn from this observation?

Correct Answer
verified

Correct Answer
verified

Suppose that Hubble's constant were 20 kilometers per second per million light-years. How fast would we expect a galaxy 100 million light-years away to be moving? (Assume the motion is due only to Hubble's law.)

Correct Answer
verified

Most large galaxies in the universe are

Correct Answer
verified

Why can't we see past the cosmological horizon?

Correct Answer
verified

What is Hubble's law?

Correct Answer
verified

Which of the following types of galaxies have a disk and spheroidal component but lack spiral arms?

Correct Answer
verified

Correct Answer
verified
The galaxy is recedi...
View Answer

Collisions between galaxies typically unfold over a period of ________.

Correct Answer
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Which of the following is not one of the three major categories of galaxies?

Correct Answer
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Does Hubble's law work well for galaxies in the Local Group? Why or why not?

Correct Answer
verified

Suppose we observe a source of X-rays that varies substantially in brightness over a period of a few days. What can we conclude?

Correct Answer
verified

Why does the merger of two spiral galaxies often trigger starbursts?

Correct Answer
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The dusty molecular clouds in spiral gal...
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What is the most accurate way to determine the distance to a nearby star?

Correct Answer
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Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars?

Correct Answer
verified

How does a starburst end? What might happen to the galaxy afterwards?

Correct Answer
verified
A starburst might end by simply using up...
View Answer

How are jets thought to be produced by active galaxies?

Correct Answer
verified
Magnetic fields in the accreti...
View Answer

A protogalactic cloud with slow star formation is more likely to form a spiral galaxy than an elliptical galaxy.

Correct Answer
verified

Quasars radiate most of their energy as radio emission.

Correct Answer
verified

Exam 15: Galaxies and the Foundation of Modern Cosmology

Correct AnswerverifiedShow Answer

Suppose we observe a Cepheid variable in a distant galaxy. The Cepheid brightens and dims with a regular period of about 10 days. What can we learn from this observation?

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Suppose that Hubble's constant were 20 kilometers per second per million light-years. How fast would we expect a galaxy 100 million light-years away to be moving? (Assume the motion is due only to Hubble's law.)

Correct AnswerverifiedShow Answer

Most large galaxies in the universe are

Correct AnswerverifiedShow Answer

Why can't we see past the cosmological horizon?

Correct AnswerverifiedShow Answer

What is Hubble's law?

Correct AnswerverifiedShow Answer

Which of the following types of galaxies have a disk and spheroidal component but lack spiral arms?

Correct AnswerverifiedShow Answer

Correct AnswerverifiedThe galaxy is recedi...View AnswerShow Answer

Collisions between galaxies typically unfold over a period of ________.

Correct AnswerverifiedShow Answer

Which of the following is not one of the three major categories of galaxies?

Correct AnswerverifiedShow Answer

Does Hubble's law work well for galaxies in the Local Group? Why or why not?

Correct AnswerverifiedShow Answer

Suppose we observe a source of X-rays that varies substantially in brightness over a period of a few days. What can we conclude?

Correct AnswerverifiedShow Answer

Why does the merger of two spiral galaxies often trigger starbursts?

Correct AnswerverifiedThe dusty molecular clouds in spiral gal...View AnswerShow Answer

What is the most accurate way to determine the distance to a nearby star?

Correct AnswerverifiedShow Answer

Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars?

Correct AnswerverifiedShow Answer

How does a starburst end? What might happen to the galaxy afterwards?

Correct AnswerverifiedA starburst might end by simply using up...View AnswerShow Answer

How are jets thought to be produced by active galaxies?

Correct AnswerverifiedMagnetic fields in the accreti...View AnswerShow Answer

A protogalactic cloud with slow star formation is more likely to form a spiral galaxy than an elliptical galaxy.

Correct AnswerverifiedShow Answer

Quasars radiate most of their energy as radio emission.

Correct AnswerverifiedShow Answer

Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
verified

Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
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The galaxy is recedi...
View Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
The dusty molecular clouds in spiral gal...
View Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified
A starburst might end by simply using up...
View Answer

Correct Answer
verified
Magnetic fields in the accreti...
View Answer

Correct Answer
verified

Correct Answer
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