Deck 24: Black Holes and Curved Space-Time

Question 1

Once a black hole forms, the size of its event horizon is determined only by

A) the size (diameter) of the star that collapsed into the black hole
B) the mass inside the event horizon
C) the time since the black hole formed
D) the composition of the material that formed the black hole
E) you can't fool me; every black hole has an event horizon of the same size

Answer 1

the mass inside the event horizon

Question 2

The region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe, is called

A) the singularity
B) the neutron star radius
C) the gravitational redshift zone
D) the event horizon
E) day-time television

Answer 2

the event horizon

Question 3

According to Einstein's general theory of relativity, the stronger a star's gravity,

A) the weaker its pull on another star will be
B) the slower time runs near it
C) the weaker the x-rays we see from it
D) the smaller the event horizon will be of the black hole it makes
E) the less space-time around it will be distorted

Answer 3

the slower time runs near it

Question 4

The astronomer who first worked out the mathematical description of black hole event horizons was

A) Edwin Hubble
B) Jocelyn Bell
C) Karl Schwarzschild
D) S. Chandrasekhar
E) Frederik Pohl

Question 5

Suppose each of the following objects could collapse into a black hole. Each black hole would have a sphere around it that is the limit for escape -- once you are inside this region, you cannot get away. For which object would this region be the largest in diameter?

A) a star with the mass of our Sun
B) a planet like Jupiter
C) a star that was type O when it was on the main sequence
D) an entire cluster of stars (with about 150 stars in it)
E) an entire galaxy of stars (with about a billion stars in it)

Question 6

Which of the following statements about the way the mass of a white dwarf affects spacetime is correct?

A) the white dwarf mass will attract light, and pull it in a curved path; spacetime is not affected
B) the white dwarf mass will curve spacetime; light has to follow that curvature
C) the white dwarf mass will not affect spacetime at all; only black holes affect spacetime
D) the white dwarf mass will have enough gravity to straighten out any curvature in spacetime; so spacetime near the white dwarf will be flat
E) since no experiments have ever tested Einstein's theory of general relativity, it is impossible to say what will happen
Section 24.3: Tests of General Relativity

Question 7

Deep inside a black hole (and hidden from our view) is the compressed center, where all the "stuff" of the star goes. Astronomer call this central point

A) an event horizon
B) a singularity
C) a time-stopping point
D) a black dwarf
E) Bayonne, New Jersey

Question 8

In the far future, a starship becomes trapped inside the event horizon of a black hole. Although the crew discovers that their ship cannot out, they at least want to send a message to other ships in the area to stay away from the danger zone. If they send out a message in the form of a radio wave, what will be its fate?

A) the message will emerge from the event horizon with a huge gravitational redshift
B) although the radio wave will emerge from the event horizon, all the information in the message will be garbled
C) the radio wave will become a gamma ray by the time it emerges from the event horizon
D) the radio wave will only emerge from the event horizon if it is moving in the direction of the magnetic north and south pole of the star that formed the black hole
E) the message will never emerge from the event horizon

Question 9

According to the general theory of relativity, light and other radiation coming from a white dwarf or a neutron star should (and experiments show that it does) exhibit

A) reddening, where the bluer colors are more effectively absorbed or scattered by dust
B) a very strong blue shift
C) motion in a perfect circle around the white dwarf and neutron star
D) a gravitational redshift
E) absolutely no difference in characteristics when compared to light coming from any star
Section 24.5: Black Holes

Question 10

The equivalence principle (principle of equivalence) says that

A) the amount of energy released by fusion is equivalent to the amount of mass that is lost
B) gravity is equivalent the strong nuclear force is inside any nucleus
C) the effects of gravity are equivalent to the effects of acceleration
D) far away from a black hole, its pull is equivalent to the pull of the star that it formed from
E) the event horizon of a black hole is equivalent to the place where things are forever trapped

Question 11

From which of the following will a wave of light show the greatest gravitational redshift:

A) a white dwarf
B) a giant planet like Jupiter
C) Earth
D) the Sun
E) a spaceship in empty space

Question 12

If you are in a freely falling elevator near the top of a tall building, as the elevator falls, your weight would be:

A) the same as your usual weight
B) a bit less than your usual weight
C) equal to zero - you would be weightless
D) a little more than your usual weight
E) so great that you would be pressed to the floor and in great pain

Question 13

Einstein suggested that the regular change (advance) in the perihelion of the planet Mercury could be explained by:

A) the presence of a planet inside the orbit of Mercury, whose gravity influenced Mercury
B) a distortion in spacetime caused by the gravity of the Sun
C) the pull of a small black hole that orbits our Sun so closely that we are not able to see it
D) the presence of a strong magnetic field in the Sun, which causes huge outburst of material
E) a distortion in our view of the solar system caused by the Earth's atmosphere

Question 14

When astronauts aboard the International Space Station (ISS) in space let go of an orange, it just floats there. Why is that?

A) the ISS is so far from the Earth, the gravity there is essentially zero
B) the ISS is falling around the Earth, and in free fall, things feel no weight
C) spacetime is so different aboard the ISS, that time stops, and so nothing can fall
D) the law of gravity only works on the Earth, it doesn't work in space
E) this is an unsolved problem in science, and so it is "fruitless" to worry about it
Section 24.2: Spacetime and Gravity

Question 15

According to the general theory of relativity, the presence of mass

A) causes motion at the speed of light squared
B) is equivalent to the presence of light
C) causes curved paths to straighten out until they are exactly straight lines
D) causes a curvature (or warping) of spacetime
E) will cause a black hole to form, unless there is motion

Question 16

To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at?

A) mass
B) surface temperature
C) color
D) distance
E) diameter

Question 17

When Einstein proposed his General Theory of Relativity, he suggested some pretty strange ideas about space, time, and gravity. How did scientists in 1919 show that Einstein's theory described the behavior of the real world and wasn't just a crazy hypothesis?

A) by finding x-rays from a black hole
B) by using an H-R diagram for a nearby cluster of stars
C) by discovering the process of nuclear fusion
D) by dropping different weights from very tall buildings
E) by observing starlight coming close to the Sun during an eclipse
Section 24.4: Time in General Relativity

Question 18

Which of the following can a black hole not "eat" (swallow)?

A) a planet
B) a cloud of gas and dust
C) a star
D) another black hole
E) you can't fool me, black holes can eat anything

Question 19

When a light wave leaves a region of strong gravity, compared to the same wave leaving a spaceship in empty space, the wave in strong gravity will have

A) a longer wavelength
B) a lower frequency
C) less energy
D) a gravitational redshift
E) all of the above

Question 20

In 1959, Pound and Rebka did an experiment to test the prediction of Einstein's theory of general relativity about the relationship between the pace of time and the strength of gravity. When two identical atomic clocks, one on the ground floor and one on the top floor, were compared,

A) the clocks ran at exactly the same pace in both locations
B) the clock on the top floor ran a tiny bit slower
C) the clock on the ground floor ran a tiny bit slower
D) the clock on the ground floor became a little bit lighter (weighed less)
E) the clock on the top floor became a little bit lighter

Question 21

When scientists say that "black holes have no hair", what do they mean?

A) that the event horizon of a black hole is very smooth and does not have parts that jut out
B) that if you threw something toward a black hole (a rabbit, say) it would quickly be ripped apart into smaller pieces
C) that time near a black hole slows down so much our hair would not grow at a normal rate
D) that once a black hole forms, very little information can be extracted from it about the material that is now inside
E) no one knows what this means; regular people are not meant to figure out some of the weird things physicists say about black holes

Question 22

Far away from a black hole (at the distance of another star), which of the following is a possible way to detect it?

A) notice what a large amount of star light it blocks from behind it
B) look for the pulsed radio waves it gives off as it rotates like a lighthouse
C) look for the neutrinos that escape from the event horizon
D) search for flickering x-rays being given off from an accretion disk around the black hole, as it "eats" part of a neighbor star
E) you can't fool me, you can never, ever detect a black hole!

Question 23

What is a key reason that gravitational waves are so much harder to detect than electro-magnetic (e-m) waves?

A) gravitational waves don't create any kind of disturbance the way e-m waves do
B) gravitational waves are so strong, they really shake our detectors, making measurements difficult
C) gravitational waves get all mixed up with sound waves in the Earth's atmosphere, and are therefore hard to distinguish from all the sound
D) gravitational waves are much weaker than e-m waves, and therefore require very, very precise equipment to detect
E) you can't fool me; gravitational waves are much easier to detect than e-m waves

Question 24

When one member of a binary star system is a black hole, and astronomers detect flickering x-rays coming from the system, where are these x-rays usually coming from?

A) from inside the black hole event horizon
B) from the photosphere of the companion star (the star that is not a black hole)
C) from the singularity
D) from a disk of material around the black hole (material that has been pulled from the companion star and is falling toward the black hole)
E) from a distant galaxy that just happens to lie behind the black hole system (astronomers discovered that such x-rays have nothing to do with the black hole)

Question 25

The first time that astronomers observed both gravitational waves and electro-magnetic waves from the same event, what they were observing was:

A) a supernova explosion in one of the closest galaxies to us
B) the spiraling toward each other of two neutron stars
C) a binary star system where a giant star is overloading a white dwarf with too much material
D) the merger of two black holes with masses dozens of times the mass of our Sun
E) the collapse of an entire cluster of stars into one big black hole

Question 26

In the first direct detection of gravitational waves by LIGO in 2015, the waves came from

A) the collapse of a nearby star into a white dwarf
B) a supernova explosion in a nearby galaxy
C) the merger of two black holes
D) the rapid motion of three hot Jupiter planets around a nearby star
E) the dashed hopes of all the people in the U.S. who want their government to work well for them

Question 27

A handsome, rich, but vain movie star notices that he is starting to age, and consults you as his astronomy expert, to see if you can find an astronomical way to slow down his aging. Putting aside practical considerations (such as the fact that we cannot travel to other stars), which of the following strategies would IN THEORY allow him to age more slowly than the rest of humanity.

A) he should always live at sea level on Earth, and never go to any mountains or high altitudes
B) he should live far away from the gravity of any planet or star (in a deep-space station)
C) he should be in orbit around the Earth, and expose himself to as many cosmic rays as possible
D) he should travel to a black hole, and spend some time in orbit just above the event horizon
E) he should live in a room filled with positive electrical charge

Question 28

What type of main sequence star is most likely to become a black hole?

A) an O-type star
B) a G-type star
C) a K-type star
D) an M-type star
E) you can't fool me, all spectral types on the main sequence have an equal chance of becoming black holes
Section 24.6: Evidence for Black Holes

Question 29

Astronomers have concluded that growing supermassive black holes (which have millions of times the Sun's mass or more) is pretty unlikely at our location in the Milky Way Galaxy. Where do they think is the most likely place in the Milky Way for such a supermassive black hole?

A) at the outer edge of the Galaxy's disk, where there is less pull from other stars
B) where a neutron star has already formed
C) at the center of the Milky Way Galaxy, where matter is more crowded
D) at the location astronomers call Cygnus X-1
E) no place in our Galaxy is likely for a really massive black hole
Section 24.7: Gravitational Wave Astronomy

Question 30

Which of the following objects do many astronomers believe is a black hole?

A) the nebula in Orion where new stars are seen to form (from dark dust clouds)
B) the Crab Nebula
C) Cygnus X-1
D) the open cluster called the Pleiades
E) Bayonne, New Jersey

Question 31

The first, indirect detection of gravitational waves in the 1970s involved

A) a pulsar that was in the same star system with a neutron star
B) the black hole in the Cygnus X-1 system
C) a star that was swelling up to be the largest red giant astronomers had ever seen
D) a spacecraft that we purposely sent to fall into the strong gravity of the Sun
E) the collapse of a huge garbage dump in the town of Bayonne, New Jersey

Question 32

Some years after college (and after you recover from your astronomy class,) you get married and exchange gold rings with your sweetheart. What connection is there between the gold in those rings and recent observations of gravitational waves?

A) gold atoms are only produced in supernova explosions, and all the gravitational wave events we have detected so far are from supernovae
B) gold is so valuable (and so rare) because there it is only produced in the accretion disks of black holes, and most of it falls into the black hole
C) our new understanding is that significant amounts of gold in the universe are produced in the mergers of neutron stars, which can be detected with gravitational waves
D) gold is produced when two black holes merge, and most of the gravitational waves we have detected are from black hole mergers
E) this is a misleading question; there is no connection whatsoever between gold and gravitational wave events

Question 33

Wearing a very accurate watch, you volunteer to go on a mission to a black hole in a spaceship that has powerful rockets. You are able to orbit the black hole and stay a little distance outside of the event horizon. Compared to watches on Earth, your watch near the black hole will run:

A) more slowly
B) more quickly
C) infinitely slow
D) infinitely fast
E) you can't fool me, watches near a black hole don't change the pace at which they run