Question 1

Gravitational lensing occurs when __________ distorts the fabric of spacetime.

Accepted Answer

A)  a star 
B)  dark matter 
C)  a black hole 
D)  any massive object 
E)  a white dwarf 
A)  a star 
B)  dark matter 
C)  a black hole 
D)  any massive object 
E)  a white dwarf D

Question 2

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 E

Question 3

Has relatively ever been tested?

Accepted Answer

A)  No, because it would require us to set up physics experiments in faraway galaxies. 
B)  Yes, because even ordinary motion in automobiles and airplanes produces easily noticeable effects predicted by relativity. 
C)  No, because no one has been able to think of experiments that are able to measure the small differences between the predictions of Newtonian physics and relativity. 
D)  Yes, because (for example) subatomic particles can be accelerated to speeds approaching that of light. 
E)  No, because the theory of relativity contains paradoxes and contradictions, like the twin paradox. 
A)  No, because it would require us to set up physics experiments in faraway galaxies. 
B)  Yes, because even ordinary motion in automobiles and airplanes produces easily noticeable effects predicted by relativity. 
C)  No, because no one has been able to think of experiments that are able to measure the small differences between the predictions of Newtonian physics and relativity. 
D)  Yes, because (for example) subatomic particles can be accelerated to speeds approaching that of light. 
E)  No, because the theory of relativity contains paradoxes and contradictions, like the twin paradox. D

Question 4

What is the meaning of the phrase inertial frame of reference?

Accepted Answer

A)  a reference frame that is not accelerating 
B)  a reference frame that is stationary with respect to the Earth 
C)  a reference frame that is in motion at constant speed 
D)  a reference frame that is accelerating at a constant rate 
E)  a reference frame in which there are strong gravitational forces 
A)  a reference frame that is not accelerating 
B)  a reference frame that is stationary with respect to the Earth 
C)  a reference frame that is in motion at constant speed 
D)  a reference frame that is accelerating at a constant rate 
E)  a reference frame in which there are strong gravitational forces

Question 5

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 6

How might we be able to detect events like colliding neutron stars even if we don't detect any light from them?

Accepted Answer

One way to detect such an event would be

Question 7

If the Sun suddenly turned into a black hole, what would be the radius of its event horizon?

Accepted Answer

A)  3 m 
B)  30 m 
C)  300 m 
D)  3 km 
E)  30 km 
A)  3 m 
B)  30 m 
C)  300 m 
D)  3 km 
E)  30 km

Question 8

A black hole can be produced if the stellar core left over after a supernova is larger than 3 M $\odot$ .

Accepted Answer

A) True 
 B)False

Question 9

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 10

Name one verified prediction of general relativity.

Accepted Answer

A)  Spacetime is flat except inside the Schwarzschild radius of the Sun. 
B)  Relativity predicts Mercury has an orbital precession, but Newtonian physics does not. 
C)  Starlight passing near the Sun should be bent away from the Sun by its gravity. 
D)  Gravitational lensing should make Mercury brighter than it would otherwise be. 
E)  Mercury's orbital precession is a little bigger than predicted by Newtonian physics. 
A)  Spacetime is flat except inside the Schwarzschild radius of the Sun. 
B)  Relativity predicts Mercury has an orbital precession, but Newtonian physics does not. 
C)  Starlight passing near the Sun should be bent away from the Sun by its gravity. 
D)  Gravitational lensing should make Mercury brighter than it would otherwise be. 
E)  Mercury's orbital precession is a little bigger than predicted by Newtonian physics.

Question 11

According to relativity, spacecraft that can travel faster than the speed of light are:

Accepted Answer

A)  impossible, because nothing can travel that fast 
B)  possible, but not useful since they could not contain living beings 
C)  impossible, since objects that travel that fast would get shorter and squeeze out space for the astronauts to live 
D)  possible, if we are clever enough with new technologies 
E)  impossible, because they would require new energy sources that are not yet invented 
A)  impossible, because nothing can travel that fast 
B)  possible, but not useful since they could not contain living beings 
C)  impossible, since objects that travel that fast would get shorter and squeeze out space for the astronauts to live 
D)  possible, if we are clever enough with new technologies 
E)  impossible, because they would require new energy sources that are not yet invented

Question 12

While traveling the galaxy in a spacecraft, you and a colleague set out to investigate the 106M $\odot$  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 1 AU, 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)  Her signals are shifted only slightly toward the red 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)  Her signals are shifted only slightly toward the red 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 13

A red giant star is found to be orbiting an unseen object with a short orbital period. By measuring the speed at which it orbits, astronomers deduce that the object has a mass of 10M $\odot$  This object is probably a __________ because __________.

Accepted Answer

A)  black hole; the giant star is massive and could only be in orbit about something even more massive 
B)  black hole; its mass is too large to be a neutron star or a white dwarf 
C)  neutron star; any supernova that would have made a black hole would have destroyed the red giant 
D)  M-dwarf star; only such stars would be faint enough to go unseen in this system 
E)  black hole; most red giants orbit neutron stars, and neutron stars can turn into black holes 
A)  black hole; the giant star is massive and could only be in orbit about something even more massive 
B)  black hole; its mass is too large to be a neutron star or a white dwarf 
C)  neutron star; any supernova that would have made a black hole would have destroyed the red giant 
D)  M-dwarf star; only such stars would be faint enough to go unseen in this system 
E)  black hole; most red giants orbit neutron stars, and neutron stars can turn into black holes

Question 14

What does gravity mean in relativity?

Accepted Answer

A)  It is a result of mass and energy being two forms of the same thing. 
B)  It is a consequence of distances getting shorter as objects move faster. 
C)  It is the result of the mass of falling bodies getting bigger because they are in motion. 
D)  It is the force that objects with mass exert on a body. 
E)  It is the result of the distortion in spacetime around an object with any energy density. 
A)  It is a result of mass and energy being two forms of the same thing. 
B)  It is a consequence of distances getting shorter as objects move faster. 
C)  It is the result of the mass of falling bodies getting bigger because they are in motion. 
D)  It is the force that objects with mass exert on a body. 
E)  It is the result of the distortion in spacetime around an object with any energy density.

Question 15

What is the meaning of the word spacetime?

Accepted Answer

A)  It is a mental framework for keeping track of numbers in Newtonian physics. 
B)  Space and time form a two-dimensional region where physics takes place. 
C)  The term has no special meaning; it's just a fancy way to sound important when talking about physics. 
D)  It is the combined treatment of space and time in the theory of relativity. 
E)  It is the idea that observers will always measure the same locations and times of events. 
A)  It is a mental framework for keeping track of numbers in Newtonian physics. 
B)  Space and time form a two-dimensional region where physics takes place. 
C)  The term has no special meaning; it's just a fancy way to sound important when talking about physics. 
D)  It is the combined treatment of space and time in the theory of relativity. 
E)  It is the idea that observers will always measure the same locations and times of events.

Question 16

Explain how Newtonian physics is an approximation to relativity.

Accepted Answer

Newtonian physics explains many phenomen

Question 17

While traveling the galaxy in a spacecraft, you and a colleague set out to investigate the 106M $\odot$  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 18

You have a 1 kg mass at rest sitting on a lab bench in front of you. You see somebody fly by in a spaceship traveling at 0.2c. That astronaut flying by also has a 1 kg mass sitting on a bench in front of her. She would measure that mass to be 1kg.

Accepted Answer

A) True 
 B)False

Question 19

Suppose you detect a pulsar that gives us 1,000 radio pulses per second, but the pulsar is in a distant galaxy that is apparently moving away from us at 50 percent of the speed of light. An observer at rest with respect to the pulsar in that faraway galaxy would measure a pulse rate of:

Accepted Answer

A)  870 per second 
B)  1,150 per second 
C)  1,250 per second 
D)  1,366 per second 
E)  1,450 per second 
A)  870 per second 
B)  1,150 per second 
C)  1,250 per second 
D)  1,366 per second 
E)  1,450 per second

Question 20

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

Accepted Answer

A) True 
 B)False

Exam 18: Relativity and Black Holes

Gravitational lensing occurs when __________ distorts the fabric of spacetime.

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:

Has relatively ever been tested?

What is the meaning of the phrase inertial frame of reference?

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

How might we be able to detect events like colliding neutron stars even if we don't detect any light from them?

If the Sun suddenly turned into a black hole, what would be the radius of its event horizon?

A black hole can be produced if the stellar core left over after a supernova is larger than 3 M ⊙\odot⊙ .

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

Name one verified prediction of general relativity.

According to relativity, spacecraft that can travel faster than the speed of light are:

A red giant star is found to be orbiting an unseen object with a short orbital period. By measuring the speed at which it orbits, astronomers deduce that the object has a mass of 10M ⊙\odot⊙ This object is probably a __________ because __________.

What does gravity mean in relativity?

What is the meaning of the word spacetime?

Explain how Newtonian physics is an approximation to relativity.

You have a 1 kg mass at rest sitting on a lab bench in front of you. You see somebody fly by in a spaceship traveling at 0.2c. That astronaut flying by also has a 1 kg mass sitting on a bench in front of her. She would measure that mass to be 1kg.

Suppose you detect a pulsar that gives us 1,000 radio pulses per second, but the pulsar is in a distant galaxy that is apparently moving away from us at 50 percent of the speed of light. An observer at rest with respect to the pulsar in that faraway galaxy would measure a pulse rate of:

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

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 Adornmentsmoons 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

Filters

A black hole can be produced if the stellar core left over after a supernova is larger than 3 M _$\odot$ .

A red giant star is found to be orbiting an unseen object with a short orbital period. By measuring the speed at which it orbits, astronomers deduce that the object has a mass of 10M _$\odot$ This object is probably a because .