Question 1

If you had something the size of a sugar cube that was made of white dwarf matter, it would weigh .

Accepted Answer

A) as much as an average person 
B) as much as the entire Earth 
C) as much as a truck 
D) about 5 pounds 
A) as much as an average person 
B) as much as the entire Earth 
C) as much as a truck 
D) about 5 pounds

Question 2

More massive white dwarfs are smaller than less massive white dwarfs.

Accepted Answer

A) True 
 B)False

Question 3

Consider again the civilization described in the previous question. (They live on a planet orbiting 10 AU from a close binary star system that consists of a 15 MSun red giant star and a 10 MSun black hole surrounded by an accretion disk.)Through a bizarre (and scientifically unexplainable)fluctuation in the space- time continuum, a copy of a book from that civilization arrives on your desk; it is entitled Iguoonos: How We Evolved. In the first chapter, you learn that these beings evolved from organisms that lived 5 billion years ago. Which of the following statements should you expect to find as you continue to read this book?

Accepted Answer

A) Their immediate ancestors were chimpanzees. 
B) They evolved on a different planet in a different star system, and moved to their current location. 
C) They evolved from primitive wormlike creatures that had 13 legs, 4 eyes, and bald heads, thus explaining why such critters are now considered a spectacular delicacy. 
D) As a result of traumatic experiences to their evolutionary ancestors, they dislike television. 
E) They believe that the presence of two stars in their system was critical to their evolution. 
A) Their immediate ancestors were chimpanzees. 
B) They evolved on a different planet in a different star system, and moved to their current location. 
C) They evolved from primitive wormlike creatures that had 13 legs, 4 eyes, and bald heads, thus explaining why such critters are now considered a spectacular delicacy. 
D) As a result of traumatic experiences to their evolutionary ancestors, they dislike television. 
E) They believe that the presence of two stars in their system was critical to their evolution.

Question 4

What makes us think that the star system Cygnus X- 1 contains a black hole?

Accepted Answer

A) Cygnus X- 1 is a powerful X- ray burster, so it must contain a black hole. 
B) The fact that we see strong X- ray emission tells us that the system must contain a black hole. 
C) No light is emitted from this star system, so it must contain a black hole. 
D) It emits X- rays characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star. 
A) Cygnus X- 1 is a powerful X- ray burster, so it must contain a black hole. 
B) The fact that we see strong X- ray emission tells us that the system must contain a black hole. 
C) No light is emitted from this star system, so it must contain a black hole. 
D) It emits X- rays characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star.

Question 5

What is the ultimate fate of an isolated pulsar?

Accepted Answer

A) As gravity overwhelms the neutron degeneracy pressure, it will explode as a supernova. 
B) It will spin ever slower, the magnetic field will weaken, and it will become invisible. 
C) It will spin ever faster, becoming a millisecond pulsar. 
D) As gravity overwhelms the neutron degeneracy pressure, it will become a white dwarf. 
E) The neutron degeneracy pressure will eventually overwhelm gravity and the pulsar will slowly evaporate. 
A) As gravity overwhelms the neutron degeneracy pressure, it will explode as a supernova. 
B) It will spin ever slower, the magnetic field will weaken, and it will become invisible. 
C) It will spin ever faster, becoming a millisecond pulsar. 
D) As gravity overwhelms the neutron degeneracy pressure, it will become a white dwarf. 
E) The neutron degeneracy pressure will eventually overwhelm gravity and the pulsar will slowly evaporate.

Question 6

From an observational standpoint, what is a pulsar?

Accepted Answer

A) a star that slowly changes its brightness, getting dimmer and then brighter, with a period of anywhere from a few hours to a few weeks 
B) an object that emits flashes of light several times per second (or even faster), with near perfect regularity 
C) a star that changes color rapidly, from blue to red and back again 
D) an object that emits random "pulses" of light, sometimes with only a fraction of a second between pulses and other times with several days between pulses 
A) a star that slowly changes its brightness, getting dimmer and then brighter, with a period of anywhere from a few hours to a few weeks 
B) an object that emits flashes of light several times per second (or even faster), with near perfect regularity 
C) a star that changes color rapidly, from blue to red and back again 
D) an object that emits random "pulses" of light, sometimes with only a fraction of a second between pulses and other times with several days between pulses

Question 7

The Crab Pulsar is pulsing in visible light 30 times per second. Why?

Accepted Answer

A) It rotates 30 times per second. 
B) It's a mystery; no one really knows. 
C) It is eclipsed by a companion 30 times per second. 
D) A jet ejects energy and particles from a hot spot 30 times per second. 
A) It rotates 30 times per second. 
B) It's a mystery; no one really knows. 
C) It is eclipsed by a companion 30 times per second. 
D) A jet ejects energy and particles from a hot spot 30 times per second.

Question 8

When we see X- rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would rule out the possibility of a black hole?

Accepted Answer

A) bright X- ray emission that varies on a time scale of a few hours 
B) intense X- ray bursts 
C) visible and ultraviolet light from the companion star 
D) spectral lines from the companion star that alternately shift to shorter and longer wavelengths 
A) bright X- ray emission that varies on a time scale of a few hours 
B) intense X- ray bursts 
C) visible and ultraviolet light from the companion star 
D) spectral lines from the companion star that alternately shift to shorter and longer wavelengths

Question 9

According to present understanding, a nova is caused by .

Accepted Answer

A) a white dwarf that gains enough mass to exceed the 1.4- solar- mass limit 
B) hydrogen fusion on the surface of a neutron star 
C) hydrogen fusion on the surface of a white dwarf 
D) carbon fusion in the core of a white dwarf 
A) a white dwarf that gains enough mass to exceed the 1.4- solar- mass limit 
B) hydrogen fusion on the surface of a neutron star 
C) hydrogen fusion on the surface of a white dwarf 
D) carbon fusion in the core of a white dwarf

Question 10

How do we know that pulsars must be neutron stars?

Accepted Answer

A) Pulsars have the same upper mass limit as neutron stars do. 
B) Telescopic images of pulsars and neutron stars look exactly the same. 
C) No massive object, other than a neutron star, could spin as fast as we observe pulsars to spin and remain intact. 
D) We have observed massive- star supernovae produce pulsars. 
E) This is only a theory that has not yet been confirmed by observations. 
A) Pulsars have the same upper mass limit as neutron stars do. 
B) Telescopic images of pulsars and neutron stars look exactly the same. 
C) No massive object, other than a neutron star, could spin as fast as we observe pulsars to spin and remain intact. 
D) We have observed massive- star supernovae produce pulsars. 
E) This is only a theory that has not yet been confirmed by observations.

Question 11

"Negatively Defined" Objects: Summarize the best observational evidence that astronomers have for the existence of stellar mass black holes. Contrast this with the observational evidence that pulsars exist. Do you agree or disagree with the statement that the best evidence we have for stellar mass black holes is that we have detected objects for which an alternate explanation is lacking? How does your answer influence your confidence in the existence of black holes? Does the strong observational confirmation of Einstein's general theory of relativity (see Special Topic General Relativity and Spacetime in Section 14.3)increase your confidence in the existence of black holes? Should it?

Accepted Answer

The best observational evidence for the

Question 12

Consider an X- ray binary system in which a compact object, surrounded by an accretion disk, is in a binary orbit with another star. All of the following statements about such accretion disks are true except:

Accepted Answer

A) The compact object may be either a neutron star or a black hole. 
B) The radiation from an accretion disk may vary rapidly in time. 
C) The accretion disk consists of material that spills off the companion star. 
D) Several examples of flattened accretion disks being "fed" by a large companion star can be seen clearly in photos from the Hubble Space Telescope. 
E) X- rays are emitted by the hot gas in the accretion disk. 
A) The compact object may be either a neutron star or a black hole. 
B) The radiation from an accretion disk may vary rapidly in time. 
C) The accretion disk consists of material that spills off the companion star. 
D) Several examples of flattened accretion disks being "fed" by a large companion star can be seen clearly in photos from the Hubble Space Telescope. 
E) X- rays are emitted by the hot gas in the accretion disk.

Question 13

Which statement about accretion disks is not true?

Accepted Answer

A) The gas in the inner parts of the disk is hotter than the gas in the outer parts of the disk. 
B) Accretion disks are made primarily of hydrogen and helium gas. 
C) The gas in the inner parts of the disk travels faster than the gas in the outer parts of the disk. 
D) The primary factor determining whether a white dwarf has an accretion disk is the white dwarf's mass. 
A) The gas in the inner parts of the disk is hotter than the gas in the outer parts of the disk. 
B) Accretion disks are made primarily of hydrogen and helium gas. 
C) The gas in the inner parts of the disk travels faster than the gas in the outer parts of the disk. 
D) The primary factor determining whether a white dwarf has an accretion disk is the white dwarf's mass.

Question 14

Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit?

Accepted Answer

A) The white dwarf will collapse to become a black hole. 
B) The white dwarf will explode completely as a white dwarf supernova. 
C) The white dwarf will collapse in size, becoming a neutron star. 
D) The white dwarf will undergo a nova explosion. 
A) The white dwarf will collapse to become a black hole. 
B) The white dwarf will explode completely as a white dwarf supernova. 
C) The white dwarf will collapse in size, becoming a neutron star. 
D) The white dwarf will undergo a nova explosion.

Question 15

Could our Sun ever undergo a nova or a white- dwarf supernova event? Why or why not?

Accepted Answer

No, because both events can only occur w

Question 16

The Schwarzschild radius of a black hole depends on .

Accepted Answer

A) only the mass of the black hole 
B) both the mass and chemical composition of the black hole 
C) the way in which the black hole formed 
D) the observationally measured radius of the black hole 
A) only the mass of the black hole 
B) both the mass and chemical composition of the black hole 
C) the way in which the black hole formed 
D) the observationally measured radius of the black hole

If you had something the size of a sugar cube that was made of white dwarf matter, it would weigh .

More massive white dwarfs are smaller than less massive white dwarfs.

What makes us think that the star system Cygnus X- 1 contains a black hole?

What is the ultimate fate of an isolated pulsar?

From an observational standpoint, what is a pulsar?

The Crab Pulsar is pulsing in visible light 30 times per second. Why?

When we see X- rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would rule out the possibility of a black hole?

According to present understanding, a nova is caused by .

How do we know that pulsars must be neutron stars?

Consider an X- ray binary system in which a compact object, surrounded by an accretion disk, is in a binary orbit with another star. All of the following statements about such accretion disks are true except:

Which statement about accretion disks is not true?

Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit?

Could our Sun ever undergo a nova or a white- dwarf supernova event? Why or why not?

The Schwarzschild radius of a black hole depends on .

A Modern View of 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 the Solar System

Earth and the Terrestrial Worlds

Jovian Planet System

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

Other Planetary Systems: the New Science of Distant Worlds

Our Star

Surveying the Stars

Star Stuff

Our Galaxy

A Universe of Galaxies

The Birth of the Universe

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

Life in the Universe

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Exam 14: The Bizarre Stellar Graveyard

If you had something the size of a sugar cube that was made of white dwarf matter, it would weigh .

More massive white dwarfs are smaller than less massive white dwarfs.

What makes us think that the star system Cygnus X- 1 contains a black hole?

What is the ultimate fate of an isolated pulsar?

From an observational standpoint, what is a pulsar?

The Crab Pulsar is pulsing in visible light 30 times per second. Why?

When we see X- rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would rule out the possibility of a black hole?

According to present understanding, a nova is caused by .

How do we know that pulsars must be neutron stars?

Consider an X- ray binary system in which a compact object, surrounded by an accretion disk, is in a binary orbit with another star. All of the following statements about such accretion disks are true except:

Which statement about accretion disks is not true?

Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit?

Could our Sun ever undergo a nova or a white- dwarf supernova event? Why or why not?

The Schwarzschild radius of a black hole depends on .

A Modern View of 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 the Solar System

Earth and the Terrestrial Worlds

Jovian Planet System

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

Other Planetary Systems: the New Science of Distant Worlds

Our Star

Surveying the Stars

Star Stuff

Our Galaxy

A Universe of Galaxies

The Birth of the Universe

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

Life in the Universe

Filters