Question 1

How are jets thought to be produced by active galaxies?

Accepted Answer

Magnetic fields in the accreti

Question 2

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 galaxies 
A)  Globular galaxies 
B)  Elliptical galaxies 
C)  Spiral galaxies 
D)  Irregular galaxies

Question 3

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. 
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.

Question 4

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 5

Most large galaxies in the universe are

Accepted Answer

A)  elliptical. 
B)  spiral or lenticular. 
C)  irregular. 
D)  abnormal. 
A)  elliptical. 
B)  spiral or lenticular. 
C)  irregular. 
D)  abnormal.

Question 6

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

Accepted Answer

The dusty molecular clouds in spiral gal

Question 7

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. 
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.

Question 8

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

Question 9

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. 
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.

Question 10

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/s 
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/s

Question 11

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 above 
A)  ellipticals 
B)  lenticulars 
C)  irregulars 
D)  all of the above

Question 12

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. 
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.

Question 13

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

Question 14

Quasars radiate most of their energy as radio emission.

Accepted Answer

A) True 
 B)False

Question 15

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 16

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. 
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.

Question 17

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. 
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.

Question 18

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. 
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.

Question 19

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

Question 20

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

Accepted Answer

A starburst might end by simply using up

How are jets thought to be produced by active galaxies?

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

Most large galaxies in the universe are

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

What is Hubble's law?

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

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

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.)

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

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

Collisions between galaxies typically unfold over a period of ________.

Quasars radiate most of their energy as radio emission.

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

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?

Why can't we see past the cosmological horizon?

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

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

Our Place in the Universe

Discovering the Universe for Yourself

The Science of Astronomy

Making Sense of the Universe: Understanding Motion, Energy, and Gravity

Light: the Cosmic Messenger

Formation of Planetary Systems: Our Solar System and Beyond

Earth and the Terrestrial Worlds

Jovian Planet Systems

Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts

Our Star

Surveying the Stars

Star Stuff

Bizarre Stellar Graveyard

Our Galaxy

Dark Matter, Dark Energy, and the Fate of the Universe

The Beginning of Time

Life in the Universe

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Exam 15: Galaxies and the Foundation of Modern Cosmology

How are jets thought to be produced by active galaxies?

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

Most large galaxies in the universe are

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

What is Hubble's law?

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

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

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.)

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

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

Collisions between galaxies typically unfold over a period of ________.

Quasars radiate most of their energy as radio emission.

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

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?

Why can't we see past the cosmological horizon?

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

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

Our Place in the Universe

Discovering the Universe for Yourself

The Science of Astronomy

Making Sense of the Universe: Understanding Motion, Energy, and Gravity

Light: the Cosmic Messenger

Formation of Planetary Systems: Our Solar System and Beyond

Earth and the Terrestrial Worlds

Jovian Planet Systems

Asteroids, Comets, and Dwarf Planets: Their Nature, Orbits, and Impacts

Our Star

Surveying the Stars

Star Stuff

Bizarre Stellar Graveyard

Our Galaxy

Dark Matter, Dark Energy, and the Fate of the Universe

The Beginning of Time

Life in the Universe

Filters