Question 1

A white dwarf is

Accepted Answer

A) a precursor to a black hole. 
B) an early stage of a neutron star. 
C) what most stars become when they die. 
D) a brown dwarf that has exhausted its fuel for nuclear fusion. 
A) a precursor to a black hole. 
B) an early stage of a neutron star. 
C) what most stars become when they die. 
D) a brown dwarf that has exhausted its fuel for nuclear fusion.

Question 2

Suppose you find an X-ray binary that exhibits X-ray bursts.Is it possible that the system's X-ray binary consists of a red giant and a black hole? Why or why not?

Accepted Answer

No,because bursts oc

Question 3

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

Question 4

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

Question 5

At the end of its life,what kind of pressure will support our Sun?

Accepted Answer

A) neutron degeneracy pressure 
B) quark degeneracy pressure 
C) electron degeneracy pressure 
D) pressure from interstellar dust particles 
A) neutron degeneracy pressure 
B) quark degeneracy pressure 
C) electron degeneracy pressure 
D) pressure from interstellar dust particles

Question 6

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 hometown?

Accepted Answer

A) The entire mass of 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 through Earth,creating a large crater,and exit Earth on the other side. 
E) It would crash into Earth,throwing vast amounts of dust into the atmosphere which in turn would cool Earth.Such a scenario is probably what caused the extinction of the dinosaurs. 
A) The entire mass of 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 through Earth,creating a large crater,and exit Earth on the other side. 
E) It would crash into Earth,throwing vast amounts of dust into the atmosphere which in turn would cool Earth.Such a scenario is probably what caused the extinction of the dinosaurs.

Question 7

What is the ultimate fate of an isolated pulsar?

Accepted Answer

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

Question 8

According to our modern understanding,what is a nova?

Accepted Answer

A) an explosion on the surface of a white dwarf in a close binary system 
B) the explosion of a massive star at the end of its life 
C) the sudden formation of a new star in the sky 
D) a rapidly spinning neutron star 
A) an explosion on the surface of a white dwarf in a close binary system 
B) the explosion of a massive star at the end of its life 
C) the sudden formation of a new star in the sky 
D) a rapidly spinning neutron star

Question 9

Imagine an advanced civilization living on a planet orbiting at a distance of 10 AU (1.5 billion kilometers)from a close binary star system that consists of a 15 MSᵤn red giant star and a 10 MSᵤn black hole.The black hole is surrounded by an accretion disk.Sometime within the next million years or so,the civilization's planet is likely to be doomed because

Accepted Answer

A) the red giant will probably supernova within the next million years. 
B) jets of material shot out of the accretion disk will shoot down their planet. 
C) the red giant star,which provides most of energy the civilization needs to exist,will soon be destroyed in the accretion disk. 
D) tidal forces from the black hole will rip the planet apart. 
A) the red giant will probably supernova within the next million years. 
B) jets of material shot out of the accretion disk will shoot down their planet. 
C) the red giant star,which provides most of energy the civilization needs to exist,will soon be destroyed in the accretion disk. 
D) tidal forces from the black hole will rip the planet apart.

Question 10

The upper limit to the mass of a white dwarf is 1.4 solar masses.

Accepted Answer

A) True 
 B)False

Question 11

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 12

Which of the following statements about gamma ray bursts is not true?

Accepted Answer

A) Gamma ray bursts are among the most luminous events that ever occur in the universe. 
B) The events responsible for gamma ray bursts apparently produce only gamma rays,and no other light that we can hope to detect. 
C) Gamma ray bursts were originally discovered by satellites designed to look for signs of nuclear bomb tests on Earth. 
D) Based on their distribution in the sky,we can rule out a connection between gamma ray bursts and X-ray binaries in the Milky Way Galaxy. 
A) Gamma ray bursts are among the most luminous events that ever occur in the universe. 
B) The events responsible for gamma ray bursts apparently produce only gamma rays,and no other light that we can hope to detect. 
C) Gamma ray bursts were originally discovered by satellites designed to look for signs of nuclear bomb tests on Earth. 
D) Based on their distribution in the sky,we can rule out a connection between gamma ray bursts and X-ray binaries in the Milky Way Galaxy.

Question 13

Process of Science: Describe a hypothetical observation of a white dwarf that,if made and verified by others,would dramatically challenge our physical understanding of them.

Accepted Answer

The discovery of a w

Question 14

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

Accepted Answer

A) True 
 B)False

Question 15

Brown dwarfs,white dwarfs,and neutrons stars are all kept from collapsing by degeneracy pressure.

Accepted Answer

A) True 
 B)False

Question 16

How does a black hole form from a massive star?

Accepted Answer

A) During a supernova,if a star is massive enough for its gravity to overcome neutron degeneracy of the core,the core will be compressed until it becomes a black hole. 
B) Any star that is more massive than 8 solar masses will undergo a supernova explosion and leave behind a black-hole remnant. 
C) If enough mass is accreted by a white-dwarf star so that it exceeds the 1.4-solar-mass limit,it will undergo a supernova explosion and leave behind a black-hole remnant. 
D) If enough mass is accreted by a neutron star,it will undergo a supernova explosion and leave behind a black-hole remnant. 
E) A black hole forms when two massive main-sequence stars collide. 
A) During a supernova,if a star is massive enough for its gravity to overcome neutron degeneracy of the core,the core will be compressed until it becomes a black hole. 
B) Any star that is more massive than 8 solar masses will undergo a supernova explosion and leave behind a black-hole remnant. 
C) If enough mass is accreted by a white-dwarf star so that it exceeds the 1.4-solar-mass limit,it will undergo a supernova explosion and leave behind a black-hole remnant. 
D) If enough mass is accreted by a neutron star,it will undergo a supernova explosion and leave behind a black-hole remnant. 
E) A black hole forms when two massive main-sequence stars collide.

Question 17

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 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 Earth;this is probably what caused the extinction of the dinosaurs.

Question 18

What is the Schwarzschild radius of a 100 million-solar-mass black hole? The mass of the Sun is about 2 × 10³⁰ kg,and the formula for the Schwarzschild radius of a black hole of mass M is:Rs = $ \frac{2 \mathrm{GM}}{\mathrm{c}^{2}} $ (G = 6.67 × 10-11 $ \frac{\mathrm{m}^{3}}{\mathrm{~kg} \cdot \mathrm{s}^{2}} $ ;c= 3 × 10⁸ m/s)

Accepted Answer

A) 3 km 
B) 30 km 
C) 3,000 km 
D) 300 million km 
E) 3 million km 
A) 3 km 
B) 30 km 
C) 3,000 km 
D) 300 million km 
E) 3 million km

Question 19

Briefly describe how a nova event occurs.

Accepted Answer

A white dwarf in a close binary system a

Question 20

Suppose you drop a clock toward a black hole.As you look at the clock from a high orbit,what will you notice?

Accepted Answer

A) Time on the clock will run faster as it approaches the black hole,and light from the clock will be increasingly blueshifted. 
B) The clock will fall toward the black hole at a steady rate,so that you'll see it plunge through the event horizon within just a few minutes. 
C) The clock will fall faster and faster,reaching the speed of light as it crosses the event horizon. 
D) Time on the clock will run slower as it approaches the black hole,and light from the clock will be increasingly redshifted. 
A) Time on the clock will run faster as it approaches the black hole,and light from the clock will be increasingly blueshifted. 
B) The clock will fall toward the black hole at a steady rate,so that you'll see it plunge through the event horizon within just a few minutes. 
C) The clock will fall faster and faster,reaching the speed of light as it crosses the event horizon. 
D) Time on the clock will run slower as it approaches the black hole,and light from the clock will be increasingly redshifted.

Exam 18: The Bizarre Stellar Graveyard

A white dwarf is

Suppose you find an X-ray binary that exhibits X-ray bursts.Is it possible that the system's X-ray binary consists of a red giant and a black hole? Why or why not?

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?

At the end of its life,what kind of pressure will support our Sun?

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 hometown?

What is the ultimate fate of an isolated pulsar?

According to our modern understanding,what is a nova?

The upper limit to the mass of a white dwarf is 1.4 solar masses.

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

Which of the following statements about gamma ray bursts is not true?

Process of Science: Describe a hypothetical observation of a white dwarf that,if made and verified by others,would dramatically challenge our physical understanding of them.

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

Brown dwarfs,white dwarfs,and neutrons stars are all kept from collapsing by degeneracy pressure.

How does a black hole form from a massive star?

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?

Briefly describe how a nova event occurs.

Suppose you drop a clock toward a black hole.As you look at the clock from a high orbit,what will you notice?

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