Question 1

The event horizon of a black hole is defined as:

Accepted Answer

A) the point of maximum gravity 
B) the radius of the original neutron star before it became a black hole 
C) the radius from which shock waves course through spacetime due to the strong gravitational distortion of the black hole 
D) the radius at which the escape speed from the black hole equals the speed of light 
E) the radius at which the gravitational force is the same as that on the surface of the Sun 
A) the point of maximum gravity 
B) the radius of the original neutron star before it became a black hole 
C) the radius from which shock waves course through spacetime due to the strong gravitational distortion of the black hole 
D) the radius at which the escape speed from the black hole equals the speed of light 
E) the radius at which the gravitational force is the same as that on the surface of the Sun

Question 2

Black holes that are stellar remnants can be found by searching for:

Accepted Answer

A) dark regions at the centers of galaxies 
B) variable X-ray sources 
C) extremely luminous infrared objects 
D) objects that emit very faint radio emission 
E) regular,repeated pulsations at radio wavelengths 
A) dark regions at the centers of galaxies 
B) variable X-ray sources 
C) extremely luminous infrared objects 
D) objects that emit very faint radio emission 
E) regular,repeated pulsations at radio wavelengths

Question 3

Gamma-ray bursts are probably associated with extremely energetic supernova explosions.

Accepted Answer

A) True 
 B)False

Question 4

Photons have no mass,and Einstein's theory of general relativity says:

Accepted Answer

A) their paths through spacetime are curved in the presence of a massive body 
B) their apparent speeds depend on the observer's frame of reference 
C) they should not be attracted to a massive object 
D) their wavelengths must remain the same as they travel through spacetime 
E) their wavelengths would grow longer as they travel through empty space 
A) their paths through spacetime are curved in the presence of a massive body 
B) their apparent speeds depend on the observer's frame of reference 
C) they should not be attracted to a massive object 
D) their wavelengths must remain the same as they travel through spacetime 
E) their wavelengths would grow longer as they travel through empty space

Question 5

While traveling the galaxy in a spacecraft,you and a colleague set out to investigate the 106M⨀ black hole at the center of our galaxy.She hops aboard an escape pod and drops into a circular orbit around the black hole,maintaining a distance of 4 × 106 km,while you remain much farther away in the spacecraft.After doing some experiments to measure the strength of gravity,your colleague signals her results back to you using a green laser.What would you see? Hint: you will need to calculate the location of the event horizon.

Accepted Answer

A) You would see her signals unaltered in wavelength because she is orbiting well outside the event horizon of the black hole. 
B) You would see her signals shifted to a much redder wavelength because she is close to the event horizon. 
C) You would see nothing because your colleague has crossed the event horizon around the black hole. 
D) You would see nothing because no light can escape the gravitational pull of a black hole no matter how far she is from it. 
E) You would see her signals shifted to a much bluer wavelength because black holes can make highly energetic light. 
A) You would see her signals unaltered in wavelength because she is orbiting well outside the event horizon of the black hole. 
B) You would see her signals shifted to a much redder wavelength because she is close to the event horizon. 
C) You would see nothing because your colleague has crossed the event horizon around the black hole. 
D) You would see nothing because no light can escape the gravitational pull of a black hole no matter how far she is from it. 
E) You would see her signals shifted to a much bluer wavelength because black holes can make highly energetic light.

Question 6

Special relativity says that all observers moving at constant speed will measure the same value of the speed of light.

Accepted Answer

A) True 
 B)False

Question 7

You repeatedly measure the radial velocity of what seems to be a single main-sequence star like the Sun,but find that it is in fact orbiting in a tight orbit around another object that remains unseen.From measurement of the velocity and orbital period,you calculate that the unseen object has a mass 20 times that of the Sun-like star.Why might this object be a black hole?

Accepted Answer

If the other member of this binary syste

Question 8

If you were to design a spacecraft that could travel to the galactic center fast enough that the astronauts aboard only aged by 25 years during the trip,how fast would the spacecraft have to go? The galactic center is 25,000 light years away.

Accepted Answer

A) 0.95c 
B) 0.995c 
C) 0.99995c 
D) 0.9999995c 
E) 0.999999995c 
A) 0.95c 
B) 0.995c 
C) 0.99995c 
D) 0.9999995c 
E) 0.999999995c

Question 9

Light is increasingly redshifted near a black hole because:

Accepted Answer

A) the photons are moving away from us very quickly as they are sucked into the black hole 
B) the photons are moving increasingly faster in order to escape the pull of the black hole 
C) the photons lose energy because climbing out of the black hole's gravity makes them tired 
D) the curvature of spacetime is increasingly stretched near the black hole,which in turn stretches the wavelengths of the photons 
E) time is moving increasingly slower as viewed from the observer's frame of reference 
A) the photons are moving away from us very quickly as they are sucked into the black hole 
B) the photons are moving increasingly faster in order to escape the pull of the black hole 
C) the photons lose energy because climbing out of the black hole's gravity makes them tired 
D) the curvature of spacetime is increasingly stretched near the black hole,which in turn stretches the wavelengths of the photons 
E) time is moving increasingly slower as viewed from the observer's frame of reference

Question 10

What will observers in different inertial frames of reference always agree on?

Accepted Answer

A) how the speed of light varies with the motion of an observer 
B) the length of the meter,but not the duration of the second 
C) the rate each frame is accelerating 
D) the results of physics experiments performed in each frame 
E) whether events are simultaneous or not 
A) how the speed of light varies with the motion of an observer 
B) the length of the meter,but not the duration of the second 
C) the rate each frame is accelerating 
D) the results of physics experiments performed in each frame 
E) whether events are simultaneous or not

Question 11

What would happen if mass were continually added to a 2M⨀ neutron star?

Accepted Answer

A) The star's radius would increase. 
B) The star could eventually become a black hole. 
C) The star could erupt as a nova. 
D) The star could exceed the Chandrasekhar limit and become a Type II supernova. 
E) The star could eventually return to the top of the main sequence. 
A) The star's radius would increase. 
B) The star could eventually become a black hole. 
C) The star could erupt as a nova. 
D) The star could exceed the Chandrasekhar limit and become a Type II supernova. 
E) The star could eventually return to the top of the main sequence.

Question 12

Special relativity says that moving clocks run slower.

Accepted Answer

A) True 
 B)False

Question 13

While traveling the galaxy in a spacecraft,you and a colleague set out to investigate the 106M⨀ black hole at the center of our galaxy.He hops aboard an escape pod and drops into a circular orbit around the black hole,maintaining a distance of 10,000 km,while you remain much farther away in the spacecraft.After doing some experiments to measure the strength of gravity,your colleague signals his results back to you using a green laser.What would you see? Hint: you will need to calculate the location of the event horizon.

Accepted Answer

A) You would see his signals unaltered in wavelength because he is orbiting well outside the event horizon of the black hole. 
B) You would see his signals shifted to a much redder wavelength because he is close to the event horizon. 
C) You would see nothing,because your colleague has crossed the event horizon around the black hole. 
D) You would see nothing,because no light can escape the gravitational pull of a black hole no matter how far he is from it. 
E) You would see his signals shifted to a much bluer wavelength because black holes can make highly energetic light. 
A) You would see his signals unaltered in wavelength because he is orbiting well outside the event horizon of the black hole. 
B) You would see his signals shifted to a much redder wavelength because he is close to the event horizon. 
C) You would see nothing,because your colleague has crossed the event horizon around the black hole. 
D) You would see nothing,because no light can escape the gravitational pull of a black hole no matter how far he is from it. 
E) You would see his signals shifted to a much bluer wavelength because black holes can make highly energetic light.

Question 14

We can't detect the gravitational redshift coming from the Sun because the Sun has a very small amount of gravity.

Accepted Answer

A) True 
 B)False

Question 15

The mass of an atomic nucleus is a measure of how much energy is contained therein.

Accepted Answer

A) True 
 B)False

Question 16

Even if a black hole emitted no light,we can still detect it:

Accepted Answer

A) from sound waves produced by material falling onto the black hole 
B) by tides produced on the Earth's oceans 
C) through its Hawking radiation 
D) through its gravitational effect on surrounding gas or stars 
E) by looking for dark patches on the sky where the black hole swallows background light 
A) from sound waves produced by material falling onto the black hole 
B) by tides produced on the Earth's oceans 
C) through its Hawking radiation 
D) through its gravitational effect on surrounding gas or stars 
E) by looking for dark patches on the sky where the black hole swallows background light

Question 17

What is the equivalence principle? Describe a consequence of the equivalence principle for astronauts orbiting in the space station.

Accepted Answer

The equivalence principle states that ac

Question 18

Black holes emit no light whatsoever.

Accepted Answer

A) True 
 B)False

Question 19

If you observed that at the centers of some galaxies there were objects emitting lots of X-rays or there was gas in rapid motion,you might conclude that these galaxies:

Accepted Answer

A) are very old 
B) contain many white dwarfs 
C) have different physics than on the Earth 
D) are rotating quickly 
E) contain black holes 
A) are very old 
B) contain many white dwarfs 
C) have different physics than on the Earth 
D) are rotating quickly 
E) contain black holes

Question 20

What is the Lorentz factor for an object moving at 0.85c?

Accepted Answer

A) 1.00 
B) 1.67 
C) 1.80 
D) 1.90 
E) 2.05 
A) 1.00 
B) 1.67 
C) 1.80 
D) 1.90 
E) 2.05

Exam 18: Relativity and Black Holes

The event horizon of a black hole is defined as:

Black holes that are stellar remnants can be found by searching for:

Gamma-ray bursts are probably associated with extremely energetic supernova explosions.

Photons have no mass,and Einstein's theory of general relativity says:

Special relativity says that all observers moving at constant speed will measure the same value of the speed of light.

If you were to design a spacecraft that could travel to the galactic center fast enough that the astronauts aboard only aged by 25 years during the trip,how fast would the spacecraft have to go? The galactic center is 25,000 light years away.

Light is increasingly redshifted near a black hole because:

What will observers in different inertial frames of reference always agree on?

What would happen if mass were continually added to a 2M⨀ neutron star?

Special relativity says that moving clocks run slower.

We can't detect the gravitational redshift coming from the Sun because the Sun has a very small amount of gravity.

The mass of an atomic nucleus is a measure of how much energy is contained therein.

Even if a black hole emitted no light,we can still detect it:

What is the equivalence principle? Describe a consequence of the equivalence principle for astronauts orbiting in the space station.

Black holes emit no light whatsoever.

If you observed that at the centers of some galaxies there were objects emitting lots of X-rays or there was gas in rapid motion,you might conclude that these galaxies:

What is the Lorentz factor for an object moving at 0.85c?

Why Learn Astronomy

Patterns in the Skymotions of Earth

Motion of Astronomical Bodies

Gravity and Orbits

Light

The Tools of the Astronomer

The Birth and Evolution of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquid the Giant Planets

Planetary Adornments Moons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

Our Starthe Sun

Star Formation and the Interstellar Medium

Evolution of Low-Mass Stars

Evolution of High-Mass Stars

The Expanding Universe

Galaxies

The Milky Waya Normal Spiral Galaxy

Modern Cosmology

Large-Scale Structure in the Universe

Life

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What would happen if mass were continually added to a 2M_⨀ neutron star?