Question 1

How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf?

Accepted Answer

A)  The accretion disk around a neutron star is much hotter and emits higher-energy radiation. 
B)  The accretion disk around a neutron star is made mostly of helium while the accretion disk around a white dwarf is made mostly of hydrogen. 
C)  The accretion disk around a neutron star is more likely to give birth to planets. 
D)  The accretion disk around a neutron star always contains much more mass. 
A)  The accretion disk around a neutron star is much hotter and emits higher-energy radiation. 
B)  The accretion disk around a neutron star is made mostly of helium while the accretion disk around a white dwarf is made mostly of hydrogen. 
C)  The accretion disk around a neutron star is more likely to give birth to planets. 
D)  The accretion disk around a neutron star always contains much more mass.

Question 2

Why do white-dwarf supernovae all have the same maximum luminosity?

Accepted Answer

White-dwarf supernovae occur when the ma

Question 3

What is the basic definition of a black hole?

Accepted Answer

A)  An object with gravity so strong that not even light can escape 
B)  A dead star that has faded from view 
C)  Any object made from dark matter 
D)  A compact mass that emits no visible light 
A)  An object with gravity so strong that not even light can escape 
B)  A dead star that has faded from view 
C)  Any object made from dark matter 
D)  A compact mass that emits no visible light

Question 4

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)  X-rays are emitted by the hot gas in the accretion disk. 
B)  The accretion disk consists of material that spills off the companion star. 
C)  The compact object may be either a neutron star or a black hole. 
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)  The radiation from an accretion disk may vary rapidly in time. 
A)  X-rays are emitted by the hot gas in the accretion disk. 
B)  The accretion disk consists of material that spills off the companion star. 
C)  The compact object may be either a neutron star or a black hole. 
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)  The radiation from an accretion disk may vary rapidly in time.

Question 5

Which of the following statements about black holes is not true?

Accepted Answer

A)  If you watch someone else fall into a black hole, you will never see him or her cross the event horizon. However, he or she will fade from view as the light he or she emits becomes more and more redshifted. 
B)  If we watch a clock fall toward a black hole, we will see it tick slower and slower as it falls towards to the black hole. 
C)  The event horizon of a black hole represents a boundary from which nothing can escape. 
D)  If the Sun magically disappeared and was replaced by a black hole of the same mass, the Earth would soon be sucked into the black hole. 
E)  If you fell into a supermassive black hole (so that you could survive the tidal forces), you would experience time to be running normally as you plunged across the event horizon. 
A)  If you watch someone else fall into a black hole, you will never see him or her cross the event horizon. However, he or she will fade from view as the light he or she emits becomes more and more redshifted. 
B)  If we watch a clock fall toward a black hole, we will see it tick slower and slower as it falls towards to the black hole. 
C)  The event horizon of a black hole represents a boundary from which nothing can escape. 
D)  If the Sun magically disappeared and was replaced by a black hole of the same mass, the Earth would soon be sucked into the black hole. 
E)  If you fell into a supermassive black hole (so that you could survive the tidal forces), you would experience time to be running normally as you plunged across the event horizon.

Question 6

What do we mean by the singularity of a black hole?

Accepted Answer

A)  It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions. 
B)  It is the "point of no return" of the black hole; anything closer than this point will not be able to escape the gravitational force of the black hole. 
C)  It is the edge of the black hole, where one could leave the observable universe. 
D)  The term is intended to emphasize the fact that an object can become a black hole only once, and a black hole cannot evolve into anything else. 
A)  It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions. 
B)  It is the "point of no return" of the black hole; anything closer than this point will not be able to escape the gravitational force of the black hole. 
C)  It is the edge of the black hole, where one could leave the observable universe. 
D)  The term is intended to emphasize the fact that an object can become a black hole only once, and a black hole cannot evolve into anything else.

Question 7

Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?

Accepted Answer

A)  A massive-star supernova is brighter than a white-dwarf supernova. 
B)  A massive-star supernova happens only once, while a white-dwarf supernova can repeat periodically. 
C)  The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not. 
D)  The light of a white-dwarf supernova fades steadily, while the light of a massive-star supernova continues to brighten for many weeks. 
E)  We cannot yet tell the difference between a massive-star supernova and a white-dwarf supernova. 
A)  A massive-star supernova is brighter than a white-dwarf supernova. 
B)  A massive-star supernova happens only once, while a white-dwarf supernova can repeat periodically. 
C)  The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not. 
D)  The light of a white-dwarf supernova fades steadily, while the light of a massive-star supernova continues to brighten for many weeks. 
E)  We cannot yet tell the difference between a massive-star supernova and a white-dwarf supernova.

Question 8

What kind of star is most likely to become a white-dwarf supernova?

Accepted Answer

A)  an O star 
B)  a star like our Sun 
C)  a binary M star 
D)  a white dwarf star with a red giant binary companion 
E)  a pulsar 
A)  an O star 
B)  a star like our Sun 
C)  a binary M star 
D)  a white dwarf star with a red giant binary companion 
E)  a pulsar

Question 9

Why is there an upper limit to the mass of a white dwarf?

Accepted Answer

A)  White dwarfs come only from stars with masses less than 1.4 solar masses. 
B)  The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, and no more mass can be supported. 
C)  The more massive the white dwarf, the higher its temperature and hence the greater its degeneracy pressure. Near 1.4 solar masses, the temperature becomes so high that all matter effectively melts into subatomic particles. 
D)  The upper limit to the masses of white dwarfs was determined through observations of white dwarfs in binary systems, but no one knows why the limit exists. 
A)  White dwarfs come only from stars with masses less than 1.4 solar masses. 
B)  The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, and no more mass can be supported. 
C)  The more massive the white dwarf, the higher its temperature and hence the greater its degeneracy pressure. Near 1.4 solar masses, the temperature becomes so high that all matter effectively melts into subatomic particles. 
D)  The upper limit to the masses of white dwarfs was determined through observations of white dwarfs in binary systems, but no one knows why the limit exists.

Question 10

According to present understanding, a nova is caused by ________.

Accepted Answer

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

Question 11

Consider an object in orbit around a star. The star suddenly shrinks in size, but does not change its mass. What happens to the object's orbit?

Accepted Answer

A)  It gradually spirals into the star. 
B)  It settles into a smaller orbit, with similar distance from the surface as the original orbit. 
C)  It remains in the same orbit. 
D)  It is instantly ejected from its orbit. 
A)  It gradually spirals into the star. 
B)  It settles into a smaller orbit, with similar distance from the surface as the original orbit. 
C)  It remains in the same orbit. 
D)  It is instantly ejected from its orbit.

Question 12

Which of the following best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your home town?

Accepted Answer

A)  The entire Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. 
B)  It would rapidly sink to the center of Earth. 
C)  The combined mass of Earth and the neutron star would cause the neutron star to collapse into a black hole. 
D)  It would crash into Earth, throwing vast amounts of dust into the atmosphere that, in turn, would cool the Earth; this is probably what caused the extinction of the dinosaurs. 
A)  The entire Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star. 
B)  It would rapidly sink to the center of Earth. 
C)  The combined mass of Earth and the neutron star would cause the neutron star to collapse into a black hole. 
D)  It would crash into Earth, throwing vast amounts of dust into the atmosphere that, in turn, would cool the Earth; this is probably what caused the extinction of the dinosaurs.

Question 13

A typical neutron star is more massive than our Sun and about the size (radius) of ________.

Accepted Answer

A)  a small asteroid (10 km in diameter) 
B)  Earth 
C)  the Moon 
D)  Jupiter 
A)  a small asteroid (10 km in diameter) 
B)  Earth 
C)  the Moon 
D)  Jupiter

Question 14

A neutron star is ________.

Accepted Answer

A)  the remains of a star that died in a massive star supernova (if no black hole was created) 
B)  the remains of a star that died by expelling its outer layers in a planetary nebula 
C)  a star made mostly of elements with high atomic mass numbers, so that they have lots of neutrons 
D)  an object that will ultimately become a black hole 
A)  the remains of a star that died in a massive star supernova (if no black hole was created) 
B)  the remains of a star that died by expelling its outer layers in a planetary nebula 
C)  a star made mostly of elements with high atomic mass numbers, so that they have lots of neutrons 
D)  an object that will ultimately become a black hole

Question 15

What kind of pressure supports a white dwarf?

Accepted Answer

A)  neutron degeneracy pressure 
B)  electron degeneracy pressure 
C)  thermal pressure 
D)  radiation pressure 
E)  all of the above 
A)  neutron degeneracy pressure 
B)  electron degeneracy pressure 
C)  thermal pressure 
D)  radiation pressure 
E)  all of the above

Question 16

Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly ________.

Accepted Answer

A)  0.5 solar masses 
B)  1.4 solar masses 
C)  3 solar masses 
D)  10 solar masses 
A)  0.5 solar masses 
B)  1.4 solar masses 
C)  3 solar masses 
D)  10 solar masses

Question 17

The Schwarzschild radius of a black hole depends on ________.

Accepted Answer

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

Question 18

A white dwarf supernova leaves behind:

Accepted Answer

A)  nothing. 
B)  a neutron star or black hole. 
C)  a white dwarf. 
D)  newborn star. 
A)  nothing. 
B)  a neutron star or black hole. 
C)  a white dwarf. 
D)  newborn star.

Question 19

Suppose a white dwarf is gaining mass because of accretion from a binary companion. What happens if its mass reaches the 1.4 solar mass limit?

Accepted Answer

A)  The white dwarf undergoes a collapse and expels the excess mass in a nova eruption. 
B)  The white dwarf (which is made mostly of carbon) suddenly detonates carbon fusion and this creates a white dwarf supernova explosion. 
C)  The white dwarf immediately collapses into a black hole, disappearing from view. 
D)  A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the accreting material from reaching it in the first place. 
A)  The white dwarf undergoes a collapse and expels the excess mass in a nova eruption. 
B)  The white dwarf (which is made mostly of carbon) suddenly detonates carbon fusion and this creates a white dwarf supernova explosion. 
C)  The white dwarf immediately collapses into a black hole, disappearing from view. 
D)  A white dwarf can never gain enough mass to reach the limit because a strong stellar wind prevents the accreting material from reaching it in the first place.

Question 20

What is the origin of short gamma ray bursts?

Accepted Answer

A)  New stars forming in the Milky Way. 
B)  Supernovae in the Milky Way. 
C)  Very powerful supernovae occurring in distant galaxies. 
D)  The collision of stars in the dense nuclei of distant galaxies. 
E)  It is not known but it may be the collision of a neutron star with a black hole. 
A)  New stars forming in the Milky Way. 
B)  Supernovae in the Milky Way. 
C)  Very powerful supernovae occurring in distant galaxies. 
D)  The collision of stars in the dense nuclei of distant galaxies. 
E)  It is not known but it may be the collision of a neutron star with a black hole.

How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf?

Why do white-dwarf supernovae all have the same maximum luminosity?

What is the basic definition of a black hole?

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 of the following statements about black holes is not true?

What do we mean by the singularity of a black hole?

Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?

What kind of star is most likely to become a white-dwarf supernova?

Why is there an upper limit to the mass of a white dwarf?

According to present understanding, a nova is caused by ________.

Consider an object in orbit around a star. The star suddenly shrinks in size, but does not change its mass. What happens to the object's orbit?

Which of the following best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your home town?

A typical neutron star is more massive than our Sun and about the size (radius) of ________.

A neutron star is ________.

What kind of pressure supports a white dwarf?

Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly ________.

The Schwarzschild radius of a black hole depends on ________.

A white dwarf supernova leaves behind:

Suppose a white dwarf is gaining mass because of accretion from a binary companion. What happens if its mass reaches the 1.4 solar mass limit?

What is the origin of short gamma ray bursts?

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

Our Galaxy

Galaxies and the Foundation of Modern Cosmology

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The Beginning of Time

Life in the Universe

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Exam 13: Bizarre Stellar Graveyard

How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf?

Why do white-dwarf supernovae all have the same maximum luminosity?

What is the basic definition of a black hole?

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 of the following statements about black holes is not true?

What do we mean by the singularity of a black hole?

Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?

What kind of star is most likely to become a white-dwarf supernova?

Why is there an upper limit to the mass of a white dwarf?

According to present understanding, a nova is caused by ________.

Consider an object in orbit around a star. The star suddenly shrinks in size, but does not change its mass. What happens to the object's orbit?

Which of the following best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your home town?

A typical neutron star is more massive than our Sun and about the size (radius) of ________.

A neutron star is ________.

What kind of pressure supports a white dwarf?

Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly ________.

The Schwarzschild radius of a black hole depends on ________.

A white dwarf supernova leaves behind:

Suppose a white dwarf is gaining mass because of accretion from a binary companion. What happens if its mass reaches the 1.4 solar mass limit?

What is the origin of short gamma ray bursts?

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

Our Galaxy

Galaxies and the Foundation of Modern Cosmology

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

The Beginning of Time

Life in the Universe

Filters