Question 1

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

Accepted Answer

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

Question 2

What would happen if a small piece (say the size of a paper clip)of neutron star material struck Earth?

Accepted Answer

The answer of What would happen if a small piece...

Question 3

What causes the radio pulses of a pulsar?

Accepted Answer

A) The star vibrates. 
B) As the star spins,beams of radio radiation sweep through space.If one of the beams crosses Earth,we observe a pulse. 
C) The star undergoes periodic explosions of nuclear fusion that generate radio emission. 
D) The star's orbiting companion periodically eclipses the radio waves emitted by the main pulsar. 
E) A black hole near the star absorbs energy and re-emits it as radio waves.

Question 4

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. )One foolhardy day,a daring individual in their space force (let's call him Major Tom)decides to become the first of his species to cross the event horizon of the black hole.To add to the drama,he decides to go in wearing only a thin space suit,which offers no shielding against radiation,no cushioning against any forces,and so on.Which of the following is most likely to kill him first (or at least to start the process of killing him first)?

Accepted Answer

A) tidal forces due to the black hole 
B) X-rays from the accretion disk 
C) the crush of gravity at the singularity embedded within the black hole 
D) the sucking force from the black hole,which will cause his head to explode

Question 5

Which of the following statements about degeneracy pressure is not true?

Accepted Answer

A) Degeneracy pressure can continue to support an object against gravitational collapse even if the object becomes extremely cold. 
B) Degeneracy pressure arises from a quantum mechanical effect that we don't notice in our daily lives. 
C) Black holes form when gravity overcomes neutron degeneracy pressure. 
D) Degeneracy pressure can arise only from interactions among electrons.

Question 6

In some cases,a supernova in a binary system may lead to the eventual formation of an accretion disk around the remains of the star that exploded.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 central object about which the accretion disk swirls 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 7

What is the basic definition of a black hole?

Accepted Answer

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

Question 8

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) As a result of traumatic experiences to their evolutionary ancestors,they dislike television. 
B) Their immediate ancestors were chimpanzees. 
C) They believe that the presence of two stars in their system was critical to their evolution. 
D) 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. 
E) They evolved on a different planet in a different star system,and moved to their current location.

Question 9

A 10-solar-mass main-sequence star will produce which of the following remnants?

Accepted Answer

A) white dwarf 
B) neutron star 
C) black hole 
D) none of the above

Question 10

If you had something the size of a sugar cube that was made of neutron star matter,it would weigh

Accepted Answer

A) about 50 pounds. 
B) as much as the entire Earth. 
C) about as much as a truck. 
D) about as much as a large mountain.

Question 11

Light from white dwarfs shows a gravitational redshift.

Accepted Answer

A) True 
 B)False

Question 12

All massive-star supernovae leave behind black holes as remnants.

Accepted Answer

A) True 
 B)False

Question 13

What is the evidence that gamma-ray bursts originate from beyond the Milky Way Galaxy?

Accepted Answer

The answer of What is the evidence that gamma-ray bursts...

Question 14

Process of Science: How were neutron stars discovered?

Accepted Answer

The answer of Process of Science: How were neutron stars...

Question 15

Why do astronomers consider gamma-ray bursts to be one of the greatest mysteries in astronomy?

Accepted Answer

A) because they are so rare 
B) because we know they come from pulsating variable stars but don't know how they are created 
C) because the current evidence suggests that they are the most powerful bursts of energy that ever occur anywhere in the universe,but we don't know how they are produced 
D) because current evidence suggests that they come from our own Milky Way,but we have no idea where in the Milky Way they occur 
E) because current evidence suggests that they come from massive black holes in the centers of distant galaxies,adding to the mystery of black holes themselves

Question 16

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 brightens for many weeks. 
E) We cannot yet tell the difference between a massive-star supernova and a white-dwarf supernova.

Question 17

Process of Science: Can we ever really know what happens within the event horizon of a black hole?

Accepted Answer

The answer of Process of Science: Can we ever really...

Question 18

The Schwarzschild radius of a black hole depends on

Accepted Answer

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

Question 19

Gravitational waves that carry energy and angular momentum away from the system cause white dwarfs to gradually spiral in toward each other and merge.

Accepted Answer

A) True 
 B)False

Question 20

The maximum mass of a white dwarf is

Accepted Answer

A) about the mass of our Sun. 
B) limitless;there is no theoretical limit to the maximum mass of a white dwarf. 
C) about 3 times the mass of our Sun. 
D) about 1.4 times the mass of our Sun.

Exam 18: The Bizarre Stellar Graveyard

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

What would happen if a small piece (say the size of a paper clip)of neutron star material struck Earth?

What causes the radio pulses of a pulsar?

Which of the following statements about degeneracy pressure is not true?

In some cases,a supernova in a binary system may lead to the eventual formation of an accretion disk around the remains of the star that exploded.All of the following statements about such accretion disks are true except

What is the basic definition of a black hole?

A 10-solar-mass main-sequence star will produce which of the following remnants?

If you had something the size of a sugar cube that was made of neutron star matter,it would weigh

Light from white dwarfs shows a gravitational redshift.

All massive-star supernovae leave behind black holes as remnants.

What is the evidence that gamma-ray bursts originate from beyond the Milky Way Galaxy?

Process of Science: How were neutron stars discovered?

Why do astronomers consider gamma-ray bursts to be one of the greatest mysteries in astronomy?

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

Process of Science: Can we ever really know what happens within the event horizon of a black hole?

The Schwarzschild radius of a black hole depends on

Gravitational waves that carry energy and angular momentum away from the system cause white dwarfs to gradually spiral in toward each other and merge.

The maximum mass of a white dwarf is