Question 1

What is a primordial black hole?

Accepted Answer

A)   black hole created during the formation of the universe
B)   black hole not in orbit around a normal star
C)   black hole created during the formation of the solar system
D)   black hole at the center of a galaxy

Question 2

Suppose an astronaut is in the Space Shuttle in orbit around Earth at a speed of 7 km/s, and at some particular time the direction of travel is straight toward the Sun. The speed of light in a vacuum is 300,000 km/s. What speed will the astronaut measure for light from the Sun?

Accepted Answer

A)   300,007 km/s because the speed is added to that of the light
B)   300,014 km/s because the speed is added to that of the light, and relativistic contraction has shortened the meterstick used in the measurement of the speed of the light
C)   300,007 km/s because relativistic contraction has shortened the meterstick with which is measured the distance traveled by the light in order to measure its speed
D)   300,000 km/s

Question 3

When they merge, black holes release a burst of gravitational waves. What is the energy source for these waves?

Accepted Answer

A)   Hawking radiation
B)   the accompanying supernova
C)   the black hole orbits
D)   the accretion disk

Question 4

Expansion under high pressure and temperature results in gas from the accretion disk being propelled away from the black hole as jets. What direction do these jets take?

Accepted Answer

A)   They can take any direction except the equatorial plane, which is blocked by the accretion disk.
B)   They originate from hot spots at middle latitudes north and south of the equatorial disk.
C)   They move out along the spin axes.
D)   They move out along the magnetic axes.

Question 5

Evidence for the conclusion that the longer-living gamma-ray bursts are very distant comes from the

Accepted Answer

A)   extreme redshift of emission lines in the visible spectrum detected after a gamma-ray burst.
B)   delay in the arrival of the visible pulse behind the gamma-ray pulse, caused by the passage of the light through optically thick intergalactic material.
C)   spread in arrival times of different gamma-ray photon energies, indicating a long passage through intergalactic gas.
D)   observations of afterglows inside distant galaxies.

Question 6

What method is used by astronomers to infer the existence in space of a dark object of about 5 solar masses, such as a black hole?

Accepted Answer

A)   infrared imaging of a region whose effective temperature is lower than the cosmic microwave background, rendering it dark
B)   measurement of the gravitational redshift of spectral lines in the spectrum of the object
C)   measurement of the effect of its gravitational force on a companion object in a binary system
D)   estimation of the luminosity of the object and the application of the mass-luminosity relationship

Question 7

A space freighter accidentally drops a steel beam while passing a black hole, and the beam starts falling toward the black hole with the long direction of the beam pointing toward the black hole. What happens to the beam as it approaches the event horizon?

Accepted Answer

A)   The beam expands in all dimensions to the size of the black hole event horizon when it reaches this distance from the singularity.
B)   The beam is stretched in length and compressed in width.
C)   The beam is compressed in both length and width.
D)   The beam is compressed in length and stretched in width.

Question 8

What is the ergoregion of a Kerr black hole?

Accepted Answer

A)   region outside the event horizon where objects cannot remain at rest without falling into the black hole
B)   region inside the event horizon where virtual particles are created from the vacuum of space
C)   inner part of the accretion disk where X-rays are generated
D)   region between the event horizon and the singularity from which nothing can escape

Question 9

A clock is moving across an observer's line of sight with its face turned toward the observer. Which of these statements about this clock, as seen by the observer, is correct?

Accepted Answer

A)   The clock will run slow compared with a clock in the observer's hand.
B)   The clock will appear longer than it would if it were at rest.
C)   The clock will appear thicker, front to back, than it would if it were at rest.
D)   The clock will appear less massive than it would if it were at rest.

Question 10

According to general relativity, why does Earth orbit the Sun?

Accepted Answer

A)   Matter contains quarks, and Earth and the Sun attract each other with the "color force" between their quarks.
B)   Space around the Sun is curved, and Earth follows a geodesic in this curved space.
C)   The Sun exerts a gravitational force on Earth across empty space.
D)   Earth and the Sun are continually exchanging photons of light in a way that holds Earth in orbit.

Question 11

A black hole is so named because

Accepted Answer

A)   no light or other electromagnetic radiation can escape from inside it.
B)   its electromagnetic radiation is gravitationally redshifted to the infrared, leaving no light in the optical region.
C)   it emits a perfect blackbody spectrum.
D)   it is colder than the rest of the universe; that is, its effective temperature is less than 3 K.

Question 12

A photon escaping FROM a large mass is gravitationally redshifted. What happens to the color of an object falling TOWARD a black hole (observed from far away) ?

Accepted Answer

A)   The color of the object will be blueshifted.
B)   The color of the object will remain unchanged.
C)   The color of the object will be redshifted because the photons reaching distant observers are escaping the vicinity of the black hole.
D)   As the object accelerates toward the black hole, moving faster and faster, the idea of color ceases to have meaning as the photons shift from visible violet to ultraviolet and then X-rays and gamma rays.

Question 13

A bomb is attached to a timer and set to explode after exactly 10 seconds. This bomb is launched at half the speed of light relative to an observer. How much time will pass for the observer before the bomb explodes?

Accepted Answer

A)   less than 10 seconds
B)   more than 10 seconds
C)   exactly 10 seconds
D)   This is impossible to answer, as it depends on the direction in which the bomb is launched.

Question 14

Which of these is NOT associated with the merger of two neutron stars?

Accepted Answer

A)   Short gamma-ray burst
B)   X-ray burster
C)   kilonova
D)   gravitational radiation

Question 15

A photon is emitted from the surface of a massive star. Which of these will the photon NOT experience as it moves away from the star?

Accepted Answer

A)   The wavelength will increase.
B)   The frequency will decrease.
C)   The speed will be reduced.
D)   The energy will be reduced.

Question 16

How many properties of the matter inside a black hole can be measured from outside the black hole?

Accepted Answer

A)   6
B)   4
C)   3
D)   only 1

Question 17

The escape velocity of matter from the center of a black hole greater than 3 solar masses is

Accepted Answer

A)   always exactly equal to the speed of light.
B)   quite small.
C)   greater than the speed of light.
D)   about half the speed of light.

Question 18

Because of the relativistic nature of spacetime in the vicinity of a black hole, a satellite orbiting the hole in one direction would have a different orbital period from a satellite orbiting in the other direction. This fact is a violation of

Accepted Answer

A)   the conservation of energy.
B)   the principle of equivalence.
C)   Kepler's third law.
D)   the conservation of angular momentum.

Question 19

The energy to create a virtual particle-antiparticle pair lasts only a short time and does not have to be accounted for in the usual conservation of energy balance. However, if the virtual particles are transformed into real particles, their energy must come from some physical source. In the case of the Hawking process, what is the source of this energy?

Accepted Answer

A)   electromagnetic waves from the black hole
B)   magnetic energy from the black hole
C)   the mass-energy of the black hole
D)   the accretion disk

Question 20

A black hole can be thought of as

Accepted Answer

A)   a star with a temperature of 0 K, emitting no light.
B)   the point at the center of every star that provides the star's energy by gravitational collapse.
C)   densely packed matter inside a small but finite volume.
D)   a region with such a large mass density that even electromagnetic radiation cannot escape.

Exam 15: Black Holes: Matters of Gravity

A bomb is attached to a timer and set to explode after exactly 10 seconds. This bomb is launched at half the speed of light relative to an observer. How much time will pass for the observer before the bomb explodes?

Correct Answer
verified

How many properties of the matter inside a black hole can be measured from outside the black hole?

Correct Answer
verified

A clock is moving across an observer's line of sight with its face turned toward the observer. Which of these statements about this clock, as seen by the observer, is correct?

Correct Answer
verified

A black hole is so named because

Correct Answer
verified

Suppose an astronaut is in the Space Shuttle in orbit around Earth at a speed of 7 km/s, and at some particular time the direction of travel is straight toward the Sun. The speed of light in a vacuum is 300,000 km/s. What speed will the astronaut measure for light from the Sun?

Correct Answer
verified

A photon is emitted from the surface of a massive star. Which of these will the photon NOT experience as it moves away from the star?

Correct Answer
verified

According to general relativity, why does Earth orbit the Sun?

Correct Answer
verified

Because of the relativistic nature of spacetime in the vicinity of a black hole, a satellite orbiting the hole in one direction would have a different orbital period from a satellite orbiting in the other direction. This fact is a violation of

Correct Answer
verified

A space freighter accidentally drops a steel beam while passing a black hole, and the beam starts falling toward the black hole with the long direction of the beam pointing toward the black hole. What happens to the beam as it approaches the event horizon?

Correct Answer
verified

What method is used by astronomers to infer the existence in space of a dark object of about 5 solar masses, such as a black hole?

Correct Answer
verified

The escape velocity of matter from the center of a black hole greater than 3 solar masses is

Correct Answer
verified

A black hole can be thought of as

Correct Answer
verified

Evidence for the conclusion that the longer-living gamma-ray bursts are very distant comes from the

Correct Answer
verified

What is the ergoregion of a Kerr black hole?

Correct Answer
verified

What is a primordial black hole?

Correct Answer
verified

Which of these is NOT associated with the merger of two neutron stars?

Correct Answer
verified

Correct Answer
verified

When they merge, black holes release a burst of gravitational waves. What is the energy source for these waves?

Correct Answer
verified

Expansion under high pressure and temperature results in gas from the accretion disk being propelled away from the black hole as jets. What direction do these jets take?

Correct Answer
verified

A photon escaping FROM a large mass is gravitationally redshifted. What happens to the color of an object falling TOWARD a black hole (observed from far away) ?

Correct Answer
verified

Exam 15: Black Holes: Matters of Gravity

A bomb is attached to a timer and set to explode after exactly 10 seconds. This bomb is launched at half the speed of light relative to an observer. How much time will pass for the observer before the bomb explodes?

Correct AnswerverifiedShow Answer

How many properties of the matter inside a black hole can be measured from outside the black hole?

Correct AnswerverifiedShow Answer

A clock is moving across an observer's line of sight with its face turned toward the observer. Which of these statements about this clock, as seen by the observer, is correct?

Correct AnswerverifiedShow Answer

A black hole is so named because

Correct AnswerverifiedShow Answer

Suppose an astronaut is in the Space Shuttle in orbit around Earth at a speed of 7 km/s, and at some particular time the direction of travel is straight toward the Sun. The speed of light in a vacuum is 300,000 km/s. What speed will the astronaut measure for light from the Sun?

Correct AnswerverifiedShow Answer

A photon is emitted from the surface of a massive star. Which of these will the photon NOT experience as it moves away from the star?

Correct AnswerverifiedShow Answer

According to general relativity, why does Earth orbit the Sun?

Correct AnswerverifiedShow Answer

Because of the relativistic nature of spacetime in the vicinity of a black hole, a satellite orbiting the hole in one direction would have a different orbital period from a satellite orbiting in the other direction. This fact is a violation of

Correct AnswerverifiedShow Answer

A space freighter accidentally drops a steel beam while passing a black hole, and the beam starts falling toward the black hole with the long direction of the beam pointing toward the black hole. What happens to the beam as it approaches the event horizon?

Correct AnswerverifiedShow Answer

What method is used by astronomers to infer the existence in space of a dark object of about 5 solar masses, such as a black hole?

Correct AnswerverifiedShow Answer

The escape velocity of matter from the center of a black hole greater than 3 solar masses is

Correct AnswerverifiedShow Answer

A black hole can be thought of as

Correct AnswerverifiedShow Answer

Evidence for the conclusion that the longer-living gamma-ray bursts are very distant comes from the

Correct AnswerverifiedShow Answer

What is the ergoregion of a Kerr black hole?

Correct AnswerverifiedShow Answer

What is a primordial black hole?

Correct AnswerverifiedShow Answer

Which of these is NOT associated with the merger of two neutron stars?

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

When they merge, black holes release a burst of gravitational waves. What is the energy source for these waves?

Correct AnswerverifiedShow Answer

Expansion under high pressure and temperature results in gas from the accretion disk being propelled away from the black hole as jets. What direction do these jets take?

Correct AnswerverifiedShow Answer

A photon escaping FROM a large mass is gravitationally redshifted. What happens to the color of an object falling TOWARD a black hole (observed from far away) ?

Correct AnswerverifiedShow Answer

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified

Correct Answer
verified