Question 1

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

Question 2

Which of the following statements is not an assumption used in models of galaxy formation?

Accepted Answer

A) The universe started out filled almost uniformly with hydrogen and helium. 
B) Some regions in the universe were slightly more dense than others. 
C) The universe is expanding. 
D) Gas contracted to form the disks of galaxies before any stars were born. 
A) The universe started out filled almost uniformly with hydrogen and helium. 
B) Some regions in the universe were slightly more dense than others. 
C) The universe is expanding. 
D) Gas contracted to form the disks of galaxies before any stars were born. C

Question 3

How is the energy that powers radio galaxies,quasars,and other active galactic nuclei produced?

Accepted Answer

A) by nuclear fusion near a central black hole 
B) by magnetic fields that trap and accelerate charged particles,which then radiate high amounts of energy 
C) by matter that has been converted to pure energy being shot out as jets by a central black hole 
D) by gravity,which converts potential energy of matter falling toward a central black hole into kinetic energy,which is then converted to thermal energy by collisions among the particles of matter 
E) by matter-antimatter annihilation near a central black hole 
A) by nuclear fusion near a central black hole 
B) by magnetic fields that trap and accelerate charged particles,which then radiate high amounts of energy 
C) by matter that has been converted to pure energy being shot out as jets by a central black hole 
D) by gravity,which converts potential energy of matter falling toward a central black hole into kinetic energy,which is then converted to thermal energy by collisions among the particles of matter 
E) by matter-antimatter annihilation near a central black hole D

Question 4

Why should galaxy collisions have been more common in the past than they are today?

Accepted Answer

A) Galaxies were more active in the past and therefore would have collided with each other more frequently. 
B) Galaxies were much bigger in the past since they had not contracted completely. 
C) Galaxies were closer together in the past because the universe was smaller. 
D) Galaxies attracted each other more strongly in the past because they were more massive;they had not yet turned most of their mass into stars and light. 
E) Galaxy collisions shouldn't have been more common in the past than they are now. 
A) Galaxies were more active in the past and therefore would have collided with each other more frequently. 
B) Galaxies were much bigger in the past since they had not contracted completely. 
C) Galaxies were closer together in the past because the universe was smaller. 
D) Galaxies attracted each other more strongly in the past because they were more massive;they had not yet turned most of their mass into stars and light. 
E) Galaxy collisions shouldn't have been more common in the past than they are now.

Question 5

The best evidence for the existence of supermassive black holes is

Accepted Answer

A) very high orbital velocities in a very compact region. 
B) evidence for jet velocities that approach the speed of light. 
C) large quantities of high-energy emission such as X-rays and gamma rays,and radio emission from relativistic electrons. 
D) huge dark regions in the centers of galaxies,where black holes have been sucking in the galaxy from the inside out. 
A) very high orbital velocities in a very compact region. 
B) evidence for jet velocities that approach the speed of light. 
C) large quantities of high-energy emission such as X-rays and gamma rays,and radio emission from relativistic electrons. 
D) huge dark regions in the centers of galaxies,where black holes have been sucking in the galaxy from the inside out.

Question 6

What is a quasar?

Accepted Answer

A) a starlike object that actually represents a bright patch of gas in the Milky Way 
B) a very large galaxy thought to be formed by the merger of several smaller galaxies,typically found in the center of a galaxy cluster 
C) a specialized astronomical instrument for observing distant stars 
D) the extremely bright center of a distant galaxy,thought to be powered by a supermassive black hole 
E) another name for very bright stars of spectral type O 
A) a starlike object that actually represents a bright patch of gas in the Milky Way 
B) a very large galaxy thought to be formed by the merger of several smaller galaxies,typically found in the center of a galaxy cluster 
C) a specialized astronomical instrument for observing distant stars 
D) the extremely bright center of a distant galaxy,thought to be powered by a supermassive black hole 
E) another name for very bright stars of spectral type O

Question 7

Process of Science: In the discovery of quasars,the radio source 3C273 was found to have strong emission lines at wavelengths that did not correspond to any known element on Earth.Suppose a scientist postulated that they had discovered a new element that only existed in these powerful radio sources.How would you test this?

Accepted Answer

You would expect to see the sa

Question 8

Quasars radiate most of their energy as radio emission.

Accepted Answer

A) True 
 B)False

Question 9

Two ways in which the starting conditions in a protogalactic cloud might cause it to become an elliptical (rather than spiral)galaxy are if the cloud begins with either

Accepted Answer

A) relatively little angular momentum or relatively high density. 
B) relatively high angular momentum or relatively low density. 
C) relatively high mass and a relatively low abundance of heavy elements. 
D) relatively low mass and a relatively high abundance of heavy elements. 
A) relatively little angular momentum or relatively high density. 
B) relatively high angular momentum or relatively low density. 
C) relatively high mass and a relatively low abundance of heavy elements. 
D) relatively low mass and a relatively high abundance of heavy elements.

Question 10

All of the following observations are real.Which one does not support the theory that active galactic nuclei are powered by accretion disks around massive black holes?

Accepted Answer

A) X-ray emission from active galactic nuclei can vary significantly in times as short as a few days. 
B) The total luminosity of an active galactic nucleus can be as high as about 10 billion times that of the Sun. 
C) Spectra of active galactic nuclei show that clouds of gas are orbiting a central object at very high speed. 
D) The most luminous active galactic nuclei have huge redshifts. 
A) X-ray emission from active galactic nuclei can vary significantly in times as short as a few days. 
B) The total luminosity of an active galactic nucleus can be as high as about 10 billion times that of the Sun. 
C) Spectra of active galactic nuclei show that clouds of gas are orbiting a central object at very high speed. 
D) The most luminous active galactic nuclei have huge redshifts.

Question 11

Give examples demonstrating the role of "nature" and "nurture" in galaxy evolution.

Accepted Answer

Galaxies come in a wide variety of shape

Question 12

Process of Science: What evidence do scientists have that supermassive black holes exist?

Accepted Answer

Observations of orbiting stars

Question 13

Which of the following is evidence for supermassive black holes in active galaxies?

Accepted Answer

A) the discovery of powerful jets coming from a compact core 
B) rapid changes in the luminosity of the galaxy nucleus 
C) quasars emit approximately equal power at all wavelengths from infrared to gamma rays 
D) very high speed orbital motions around galactic nuclei 
E) all of the above 
A) the discovery of powerful jets coming from a compact core 
B) rapid changes in the luminosity of the galaxy nucleus 
C) quasars emit approximately equal power at all wavelengths from infrared to gamma rays 
D) very high speed orbital motions around galactic nuclei 
E) all of the above

Question 14

Which of the following phenomena are not thought to be results of collisions or other interactions between galaxies?

Accepted Answer

A) the presence of very large,central dominant galaxies in clusters of galaxies 
B) the fact that elliptical galaxies are more common in clusters of galaxies than outside clusters 
C) starbursts 
D) the fact that spiral galaxies have both disk and halo components 
A) the presence of very large,central dominant galaxies in clusters of galaxies 
B) the fact that elliptical galaxies are more common in clusters of galaxies than outside clusters 
C) starbursts 
D) the fact that spiral galaxies have both disk and halo components

Question 15

Intergalactic hydrogen clouds are easiest to study by looking at

Accepted Answer

A) 21 cm radio emission. 
B) radio emission from molecular hydrogen. 
C) X-ray emission. 
D) absorption lines in quasar spectra. 
A) 21 cm radio emission. 
B) radio emission from molecular hydrogen. 
C) X-ray emission. 
D) absorption lines in quasar spectra.

Question 16

The distinguishing feature of a starburst galaxy is

Accepted Answer

A) the presence of an unusually large number of binary star systems containing X-ray bursters. 
B) a very large luminosity compared to the total luminosity of the Milky Way. 
C) strong radio emission from "lobes" of material well outside the visible boundaries of the galaxy. 
D) a rate of star formation that may be 100 or more times greater than that in the Milky Way. 
A) the presence of an unusually large number of binary star systems containing X-ray bursters. 
B) a very large luminosity compared to the total luminosity of the Milky Way. 
C) strong radio emission from "lobes" of material well outside the visible boundaries of the galaxy. 
D) a rate of star formation that may be 100 or more times greater than that in the Milky Way.

Question 17

A quasar's spectrum is hugely redshifted.What do most astronomers think this large redshift tells us about the quasar?

Accepted Answer

A) the composition of the quasar 
B) the distance to the quasar 
C) the size of the quasar's central,supermassive black hole 
D) the type of host galaxy in which the quasar resides 
A) the composition of the quasar 
B) the distance to the quasar 
C) the size of the quasar's central,supermassive black hole 
D) the type of host galaxy in which the quasar resides

Question 18

How do jets produced by radio galaxies differ from those of protostars?

Accepted Answer

Jets in radio galaxies differ from those

Question 19

All of the following are true.Which of these gives evidence that quasars were more common in the early stages of the universe?

Accepted Answer

A) They are more common at very great distances. 
B) They are very bright. 
C) They are active galactic nuclei. 
D) We don't see them in every galaxy. 
A) They are more common at very great distances. 
B) They are very bright. 
C) They are active galactic nuclei. 
D) We don't see them in every galaxy.

Question 20

Starburst galaxies produce most of their light in the wavelength range of

Accepted Answer

A) X-rays. 
B) the ultraviolet. 
C) the visible. 
D) the infrared. 
E) all wavelengths. 
A) X-rays. 
B) the ultraviolet. 
C) the visible. 
D) the infrared. 
E) all wavelengths.

Exam 21: Galaxy Evolution

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

Which of the following statements is not an assumption used in models of galaxy formation?

How is the energy that powers radio galaxies,quasars,and other active galactic nuclei produced?

Why should galaxy collisions have been more common in the past than they are today?

The best evidence for the existence of supermassive black holes is

What is a quasar?

Quasars radiate most of their energy as radio emission.

Two ways in which the starting conditions in a protogalactic cloud might cause it to become an elliptical (rather than spiral)galaxy are if the cloud begins with either

All of the following observations are real.Which one does not support the theory that active galactic nuclei are powered by accretion disks around massive black holes?

Give examples demonstrating the role of "nature" and "nurture" in galaxy evolution.

Process of Science: What evidence do scientists have that supermassive black holes exist?

Which of the following is evidence for supermassive black holes in active galaxies?

Which of the following phenomena are not thought to be results of collisions or other interactions between galaxies?

Intergalactic hydrogen clouds are easiest to study by looking at

The distinguishing feature of a starburst galaxy is

A quasar's spectrum is hugely redshifted.What do most astronomers think this large redshift tells us about the quasar?

How do jets produced by radio galaxies differ from those of protostars?

All of the following are true.Which of these gives evidence that quasars were more common in the early stages of the universe?

Starburst galaxies produce most of their light in the wavelength range of

A Modern View of the Universe

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The Science of Astronomy

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

Light and Matter: Reading Messages from the Cosmos

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Formation of the Solar System

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Other Planetary Systems: The New Science of Distant Worlds

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Surveying the Stars

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The Bizarre Stellar Graveyard

Our Galaxy

Galaxies and the Foundations of Modern Cosmology

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