Deck 15: Black Holes: Matters of Gravity

Question 1

What happens to the density of an object as it moves with respect to an observer as compared to the same object at rest with respect to the same observer?

A) The density will decrease.
B) The density will remain unchanged.
C) The density will increase.
D) The density can either increase or decrease depending on its direction of motion with respect to the observer.

Answer 1

The density will increase.

Question 2

Fred and Joanne both measure the length of a particular spaceship to be 100 m when it is on Earth. Joanne then gets into the spaceship and, after visiting the Moon, hurtles past Earth at a speed close to the speed of light. Fred, still on Earth, measures the length of the moving spaceship to be about 90 m. At the same time, Joanne (using her own meterstick) measures the length of the spaceship to be

A) about 90 m because of the motion of the spaceship.
B) 100 m because she is "at rest" on the spaceship.
C) It cannot be concluded from the information given.
D) about 110 m because both she and the spaceship are moving.

Answer 2

100 m because she is "at rest" on the spaceship.

Question 3

Suppose an observer sees a spaceship with a clock on it hurtling past them at 80% of the speed of light. As it goes by, the second hand on the ship's clock ticks off 5 seconds. How much time elapsed on the observer's clock during this occurrence?

A) more than 5 seconds if the spaceship is approaching the observer and less than 5 seconds if it is moving away from the observer
B) less than 5 seconds
C) more than 5 seconds
D) 5 seconds-the same as on the ship's clock

Answer 3

more than 5 seconds

Question 4

If Alice stays on Earth while Bob races off in a rocket at a speed close to the speed of light, then, according to special relativity Alice will see a clock on the rocket appear to tick more slowly than the one on her wall. If Bob looks back at Alice's wall clock, then according to the same theory Bob will see the wall clock appear to tick

A) at the same speed as the clock on the rocket.
B) faster than the clock on the rocket.
C) faster or slower than the clock on the rocket, depending on the direction of travel of the rocket compared with Earth.
D) slower than the clock on the rocket.

Question 5

Two spaceships are traveling past Earth at 90% of the speed of light in opposite directions (i.e., they are approaching each other). One spaceship turns on a searchlight, which is seen by scientists aboard the other. What speed do the scientists measure for this light (c = speed of light in a vacuum)?

A) 1.9 c (equal to c + 0.9 c)
B) 1.8 c (equal to 2 *0.9 c).
C) c
D) 0.9 c

Question 6

Suppose a person is in a jet airliner traveling at a constant speed of 400 km/h in a constant direction. All windows are blocked, so they cannot see outside, and there are no vibrations from the engines. What experiment can be done to determine that they are in fact moving?

A) Suspend a ball by a thread from the ceiling and measure the angle the thread makes with the vertical.
B) None-all experiments will give the same results that one would get when at rest on the ground.
C) Measure the speed of a sound wave traveling up the aisle (toward the nose of the aircraft) and another traveling down toward the tail, and calculate the difference between the two results.
D) Drop a small rock and measure the distance it moves backward down the aisle as it falls.

Question 7

In a TV tube, the picture is created by a beam of electrons that travels down the tube at a very high speed. What is the mass of one of these electrons, compared with an electron at rest?

A) The mass of an electron is measured to be the same regardless of how fast it is moving.
B) The moving electron appears to have a smaller mass.
C) The electron appears to have a greater mass if one is in front of the tube (electrons approaching) and a smaller mass if one is standing behind the tube (electrons moving away).
D) The moving electron appears to have a greater mass.

Question 8

Einstein's theory of special relativity contains some very strange ideas such as time dilation (moving clocks run slow), length contraction (moving lengths are shorter), and lack of absolute simultaneity. What is the basis of these ideas?

A) New technologies allow more precise measurements of length and time than had been possible in Newton's era, and the theory had to be reworked to fit this new evidence.
B) The speed of light is the same for all observers in all reference frames.
C) The ether (the medium that supports the passage of light) proved to be denser than originally thought.
D) The fabric of spacetime is dominated by black holes.

Question 9

A student is on Mars standing on the gangplank of a spaceship when she sees an identical spaceship go past Mars at 90% of the speed of light. When she looks closely at this spaceship, how does it compare with her own spaceship?

A) The moving spaceship appears to be shorter than hers, and time on it appears to move more slowly than on her ship.
B) The moving spaceship appears to be shorter than hers, and time on it appears to move more quickly than on her ship.
C) The moving spaceship appears to be longer than hers, and time on it appears to move more quickly than on her ship.
D) The moving spaceship appears to be longer than hers, and time on it appears to move more slowly than on her ship.

Question 10

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?

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 11

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?

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 12

A clock with a luminous dial is moving toward an observer at a speed that is a large fraction of the speed of light. Which of these will the observer measure?

A) The light emitted by the clock will be shifted toward longer wavelengths compared to those seen by an observer moving with the clock.
B) The light from the clock is approaching the observer at speed c.
C) The clock runs fast compared to an identical clock at rest in the observer's hand.
D) The clock appears thicker, front to back, than the identical clock in observer's hand.

Question 13

Which of these statements is NOT a consequence of the postulates of special relativity?

A) The mass of an object moving with respect to an observer is larger than the mass measured by a different observer who is at rest with respect to the object.
B) A clock moving with respect to an observer ticks more slowly than when measured by an observer who is moving along with the clock.
C) The length of an object moving with respect to an observer is shorter than it is when measured by a different observer moving along with the object.
D) The wavelength emitted from a source moving with respect to an observer is different from the wavelength measured by an observer who is moving along with the source.

Question 14

A spacecraft has a length of 2 meters if it is measured at rest. The spacecraft moves past an observer at half the speed of light. What will the observer measure the spacecraft's length to be?

A) less than 10 meters
B) more than 10 meters
C) exactly 10 meters
D) The answer will depend on whether the observer measures the length while it is moving toward or away from them.

Question 15

If an observer sees an object moving past them at 90% of the speed of light, what will its length appear to be?

A) The object will look longer than if it were at rest.
B) The object will look shorter than if it were at rest.
C) The object will look shorter than if it were at rest while it is coming toward them and longer after it has passed them.
D) The length of the object will appear to be unchanged from when it is at rest since it is a solid object.

Question 16

Suppose an astronaut is aboard a spaceship that is passing Earth at 80% of the speed of light. The astronaut sees a clock on Earth tick off 5 seconds. How much time elapses on the astronaut's own clock while this is happening?

A) 5 seconds-the same as on the ship's clock
B) more than 5 seconds
C) more than 5 seconds if the astronaut is approaching Earth and less than 5 seconds if the astronaut is moving away from Earth
D) less than 5 seconds

Question 17

Suppose astronauts are in a spaceship traveling toward Earth at 95% of the speed of light. Compared with when the ship was at rest on Mars, what length do the astronauts measure for their spaceship?

A) It cannot be determined; their life processes have slowed down too much for them to measure the length.
B) same
C) shorter
D) longer

Question 18

Which of these is a correct and complete statement of Einstein's first postulate of special relativity?

A) One's description of physical reality is the same regardless of the constant velocity at which one moves.
B) One's description of physical reality is the same regardless of the direction in which one moves, even if the speed changes.
C) One's description of physical reality is the same regardless of how one moves.
D) One's description of physical reality is the same regardless of the constant speed at which one moves, even if direction changes.

Question 19

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?

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 20

A child on a playground swing is swinging back and forth (one complete oscillation) once every 4 seconds, as seen by her father standing next to the swing. At the same time, a spaceship is hurtling by at a speed close to the speed of light. According to special relativity (and ignoring the Doppler effect for this question), her mother on the spaceship finds that the time for one full swing is

A) less than 4 seconds when the spaceship is approaching the swing and more than 4 seconds when it is moving away.
B) less than 4 seconds.
C) equal to 4 seconds.
D) more than 4 seconds.

Question 21

Suppose an astronaut is far from a planet with a very strong gravitational field. The astronaut is also watching a clock on the surface of this planet. During the time in which his own clock ticks out a time of 1 hour, how much time does the clock on the planet tick out?

A) less than 1 hour (but more than zero)
B) no time at all
C) more than 1 hour
D) exactly 1 hour, the same as the astronaut's clock

Question 22

Suppose a satellite were placed in orbit around (and very close to) a neutron star. Which theory would one need to use to describe how it moves?

A) special theory of relativity
B) general theory of relativity
C) Kepler's laws
D) Newton's law of gravitation

Question 23

If astronomers want to measure the mass of a star or a planet, they usually rely on the orbital motion of a satellite or binary companion. Which of these is the basis for a mass measurement of a solitary mass?

A) time dilation
B) length contraction
C) gravitational redshift
D) geodesics

Question 24

What property of matter does general relativity address that is NOT included in special relativity?

A) acceleration
B) color
C) mass
D) temperature

Question 25

How does a gravitational field affect the passage of time?

A) Gravity has no effect on the passage of time.
B) Clocks in a gravitational field run slower than clocks farther from the center of the field when viewed by an observer who is also farther from the center of the field.
C) Gravity makes time stop.
D) Clocks in a gravitational field run faster than clocks farther from the center of the field when viewed by an observer who is also farther from the center of the field.

Question 26

In which of these locations would a clock run at its fastest rate?

A) empty space, far from any planets or stars
B) Earth's surface
C) Jupiter's atmosphere
D) "weightless" environment on the Space Shuttle in orbit around Earth

Question 27

According to Einstein's theory of general relativity, if one watches a clock from a distant location as it is moved closer to a source of gravity, one will see the clock

A) maintain the same rate because time is unaffected by gravity.
B) change its rate if it is moving rapidly but maintain its standard rate if it is stationary in a gravity field.
C) slow down.
D) run faster.

Question 28

According to Newton's law of gravity, why does Earth orbit the Sun?

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

Question 29

An electromagnetic wave leaves the surface of a neutron star and travels outward. As the wave gets farther from the star's surface, the _____ and the _____.

A) speed decreases; wavelength increases
B) frequency increases; wavelength decreases
C) frequency decreases; wavelength increases
D) speed decreases; frequency decreases

Question 30

What happens to the wavelength of light as it travels outward through the gravitational field of a planet or star so that the field becomes less strong?

A) The wavelength stays the same, but the intensity of the light decreases.
B) The wavelength decreases.
C) The wavelength stays the same, but the energy of each photon decreases.
D) The wavelength increases.

Question 31

At which of these locations will Newton's laws of motion be MOST inadequate in describing precisely the motions of objects?

A) in the Space Shuttle, moving around Earth at a speed of about 8 km/sec
B) at the center of Earth
C) inside an artillery shell as it accelerates inside the gun barrel
D) inside the orbit of Mercury

Question 32

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

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 33

How must an object be moving for one to be able to use the theory of special relativity to describe the object?

A) The object must be moving close to the speed of light; how speed and direction change is not important.
B) The object must be moving at a constant speed in a straight line; how fast it is moving is not important.
C) The object must be moving in a constant direction; how its speed changes is unimportant.
D) The object must be moving at a constant speed; whether the direction of motion changes is unimportant.

Question 34

In what way is the general theory of relativity more "general" (i.e., deals with more situations) than the special theory of relativity?

A) The general theory includes gravitation and accelerated motion.
B) The general theory includes the change in the rate of passage of time when objects are in motion.
C) The general theory includes motion at and above the speed of light.
D) The general theory includes only constant, unaccelerated motion.

Question 35

In the language of general relativity, what is usually called "gravitational force" is described in terms of

A) time dilation.
B) length contraction.
C) gravitational redshift.
D) the curvature of spacetime.

Question 36

Suppose that a clock is carefully calibrated to tick at a regular rate. If one is brought inside a strong gravitational field, an observer far from that gravitational field would measure the clock to tick

A) at the same rate in a gravitational field if it is an atomic clock but at a slower rate if it is a mechanical clock.
B) at the same rate, wherever it is placed in a gravitational field.
C) slower the closer it comes to the source of gravity.
D) faster the closer it comes to the source of gravity.

Question 37

Suppose an observer were far from a planet that had a very strong gravitational field, and a light wave reaches the observer from a source of hydrogen (H _$\alpha$ ) light on the surface of the planet. For an H _$\alpha$ light source in the observer's own spaceship, the wavelength is 656.3 nm. What wavelength does the observer see when looking at the light source on the planet?

A) shorter than 656.3 nm
B) longer than 656.3 nm
C) infinite, since the source is in a gravitational field
D) 656.3 nm, the same as from the spaceship's light source

Question 38

In an observation of a group of stars adjacent to the limb of the Sun during a total solar eclipse, which way will the nearest star to the solar limb appear to move because of the curvature of space near the Sun?

A) away from the Sun
B) toward the center of the Sun
C) in a direction parallel to the limb of the Sun
D) Light is unaffected by the curvature of space, so the star's position in the group will remain unchanged.

Question 39

A scientist is going to make measurements of these entities. For which one will Newtonian physics give answers that are precise enough for practical use?

A) the advance of the perihelion of the orbit of Mercury
B) the orbit of a satellite around Earth
C) two neutron stars orbiting each other
D) GPS locations on Earth from orbiting satellites

Question 40

Why does Einstein's theory of special relativity carry the name "special"?

A) The theory deals only with motion at speeds significantly less than the speed of light.
B) The theory deals only with objects that are at rest relative to each other.
C) The theory deals only with gravity, not with other kinds of forces.
D) The theory deals only with objects moving in a straight line at a constant speed.

Question 41

A black hole is so named because

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 42

In a binary star system, an unseen component is found to have 8 solar masses. It would be visible if the system were a normal star, so it must be a collapsed object. Theoretical considerations declare that it must be a

A) black hole.
B) neutron star.
C) white dwarf.
D) brown dwarf.

Question 43

What happens to a photon that leaves the interior of a black hole aimed directly upward (radially outward)?

A) This photon will be stopped and pulled back downward by the gravity of the black hole.
B) Since symmetry prohibits this photon from deflecting to either side, this is the only case in which a photon can escape from a black hole. But since it must be aimed precisely upward, this is a vanishingly small fraction of all the light inside the black hole.
C) This photon reflects from the ergoregion back to the singularity where it is absorbed.
D) This photon becomes infinitely redshifted and loses all its energy.

Question 44

Which of these statements is NOT an observation confirming the predictions of general relativity?

A) Light is deflected in the curved space near the Sun.
B) The perihelion of the orbit of Mercury shifts more than the amount predicted by Newtonian physics.
C) Primordial black holes have been detected.
D) The spectra of stars exhibit the gravitational redshift.

Question 45

Which of these measurements is the lower limit for a main-sequence star that will eventually form a black hole?

A) 50 solar masses
B) 25 solar masses
C) 3 solar masses
D) 1.4 solar masses

Question 46

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?

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

Question 47

What is a singularity?

A) particle-antiparticle pair
B) tunnel into another universe
C) point at the Schwarzschild radius of a black hole
D) point of infinite density

Question 48

A black hole is so named because

A) the gravitational field is so high that the wavelength of its emitted light is gravitationally redshifted to radio wavelengths.
B) it emits no visible light because it is so cold, less than 100 K.
C) no light can escape from it due to its powerful gravitational field.
D) it is colder than the rest of the universe; that is, its effective temperature is less than 3 K.

Question 49

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

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 50

What physical theory has been developed to describe adequately the details of what happens inside a black hole?

A) general relativity
B) quantum theory
C) electromagnetism
D) None of these answers are correct.

Question 51

The escape velocity for material inside a black hole is

A) zero.
B) infinite.
C) greater than the speed of light.
D) twice that from a neutron star.

Question 52

What is the likely final fate of a star of 30 solar masses when it is on the main sequence?

A) The star will collapse and become a black hole.
B) The star will condense to the point where it is composed completely of neutrons, the degeneracy of which will prevent further shrinkage.
C) The degeneracy of the electrons within the star will prevent collapse below the diameter of a white dwarf.
D) The star will immediately split in two and become a binary star system.

Question 53

One feature that distinguishes a black hole from all other objects in the universe is that

A) the escape velocity from inside a black hole is greater than the speed of light.
B) a black hole emits large quantities of X-rays.
C) a black hole exceeds 3 solar masses.
D) the shape of the gravitational field of a black hole is different from that of an ordinary massive object, even at large distances from it.

Question 54

A black hole can be thought of as

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.

Question 55

In a binary star system, one component is found to have about 3 solar masses, the other about 7 solar masses. The 3-solar-mass star is visible from Earth, but the 7-solar-mass star is not. Theoretical considerations declare that the 7-solar-mass star must be a

A) neutron star.
B) cool planetary object.
C) white dwarf.
D) black hole.

Question 56

What is believed to be the maximum mass for a neutron star?

A) 150 solar masses
B) 12 solar masses
C) 1.4 solar mass
D) 3 solar masses

Question 57

In the context of black holes, a singularity is a(n)

A) place just outside the event horizon of a rotating black hole where it is impossible to remain at rest.
B) entry point in the event horizon of a black hole through which material is allowed to pass unhindered.
C) place where a nonzero mass occupies zero volume.
D) place where the escape velocity exactly equals the speed of light.

Question 58

Which of these is NOT a test of general relativity but rather a test of special relativity?

A) The length of a moving object decreases when observed by a stationary observer.
B) The wavelength of light increases as it leaves a region of gravitational field.
C) Light travels in a curved path in a gravitational field.
D) The perihelion position of Mercury's orbit precesses more quickly than is predicted by Newtonian theory.

Question 59

Suppose that a neutron star of 2.9 solar masses is part of a binary star system in which the other star is a normal giant star. What would happen if 1 solar mass of material were transferred onto the neutron star from its companion?

A) The neutron star would explode as a supernova.
B) The neutron degeneracy pressure inside the neutron star would increase to balance the increased gravitational force in the neutron star.
C) The increased gravitational force would transform the neutrons into quarks, and the neutron star would reestablish equilibrium as a quark star of smaller diameter.
D) The neutron star would collapse and become a black hole.

Question 60

Light leaving the surface of a neutron star is strongly redshifted. What name is given to this effect?

A) cosmological redshift
B) gravitational redshift
C) Zeeman effect
D) Doppler shift

Question 61

What is a superstring?

A) new kind of force postulated to keep a companion binary star from falling into a black hole
B) line of material along which the jets shoot out from neutron stars and black holes
C) new theory of physics that may describe what happens inside the event horizon of a black hole
D) force that holds quarks together in a quark star

Question 62

Where is the event horizon of a black hole located?

A) position of maximum X-ray emission
B) singularity
C) outer surface of the ergoregion
D) Schwarzschild radius away from its center

Question 63

Place two identical 3-solar-mass black holes side by side. Add 1 solar mass of neutrons to the left-hand one and 1 solar mass of protons to the right-hand one. How will these two black holes differ?

A) The black holes will not differ at all since protons and neutrons are transformed into a common type of uncharged matter.
B) The left-hand black hole will have a stronger gravitational field than the right-hand one because a neutron is heavier than a proton.
C) The left-hand black hole will emit electrons and neutrinos as its neutrons decay into protons.
D) The left-hand black hole will be electrically neutral and the right-hand one will have an enormous electric charge.

Question 64

What separates a black hole from the rest of the universe?

A) crystalline crust
B) surface of the ergoregion
C) singularity
D) event horizon

Question 65

The Schwarzschild radius is

A) half the diameter of the singularity in a black hole.
B) the distance to which gas is ejected in a planetary nebula.
C) half the diameter of a neutron star.
D) the distance from the center of a black hole to the point at which the escape velocity becomes equal to the speed of light.

Question 66

Which is the correct sequence for the end points of stellar evolution, in order of increasing mass?

A) white dwarf, black hole, neutron star
B) white dwarf, neutron star, black hole
C) neutron star, black hole, white dwarf
D) black hole, neutron star, white dwarf

Question 67

Which of these objects is NOT an end point of a star's evolutionary life?

A) red giant
B) supernova
C) black hole
D) neutron star

Question 68

The only physical properties that are necessary to describe a black hole and its interaction with the rest of the universe completely are

A) total mass, total angular momentum or spin, and temperature.
B) total mass, chemical or atomic structure of the matter within it, and overall size.
C) size of the event horizon, strength of its magnetic field, and size of its solid core.
D) total mass, total electric charge, and total angular momentum or spin.

Question 69

Suppose that a large piece (e.g., 5 solar masses) of purple, magnetized iron is rotating 5 times per day. If this object were able to collapse gravitationally to form a black hole, which of these properties of the matter inside the black hole could an outside observer actually measure?

A) rotation
B) magnetic field
C) color
D) composition

Question 70

What is the event horizon of a black hole?

A) "surface" at which any object passing through it will leave with greater energy than when it entered
B) "surface" at which all events happen
C) infinitesimally small volume at the center of the black hole that contains all of the black hole's mass
D) "surface" from inside of which nothing can escape

Question 71

At what location in the space around a black hole does the escape velocity become equal to the speed of light?

A) point where clocks are observed to slow down by a factor of 2
B) central singularity
C) event horizon
D) point where escaping X-rays are produced

Question 72

Where should an astronomer look for an event horizon?

A) in the photosphere of a star (e.g., the Sun)
B) in the magnetosphere of a neutron star
C) at the edge of the visible universe
D) near a black hole

Question 73

Which of these properties can NEVER be known about a black hole?

A) type of material inside it
B) angular momentum (spin)
C) total amount of matter (the mass) inside it
D) net electric charge

Question 74

What is the Schwarzschild radius of a black hole?

A) distance from the black hole's singularity to the point where any object entering will gain energy before leaving again
B) distance from the black hole's singularity to the point where nothing can escape from the black hole
C) distance from the black hole's singularity to the point where the X-rays are seen to originate
D) radius of the black hole's singularity

Question 75

The escape velocity at the event horizon around a black hole is

A) infinite.
B) equal to the speed of light.
C) much less than the speed of light.
D) just under the speed of light.

Question 76

What is it that is actually located at the event horizon of a black hole?

A) infinitely dense concentration of mass
B) magnetic field of immense strength
C) nothing specific
D) sphere of photons

Question 77

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

A) mass and angular momentum
B) only mass
C) mass, angular momentum, electric charge, and average atomic weight
D) mass, angular momentum, and electric charge

Question 78

Take two identical, nonrotating, 5-solar-mass black holes and place them side by side. Add 1 solar mass of pineapples to the left-hand one and 1 solar mass of uranium to the right-hand one (without changing the electrical charge or the rotation of either black hole). How will the two black holes differ?

A) The right-hand black hole will have a stronger gravitational field because of the denser material inside it.
B) The two black holes will not differ at all.
C) The left-hand black hole will smell better.
D) The right-hand black hole will be radioactive, emitting alpha particles, electrons, and gamma rays into space.

Question 79

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

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

Question 80

If an observer were to pass inward through the event horizon of a black hole, they could

A) do nothing to prevent themselves from falling directly into the singularity at the center.
B) escape again provided that the black hole is spinning.
C) move outward within the black hole with a powerful rocket, thereby avoiding the singularity until their fuel ran out, but they could never escape back out through the event horizon.
D) avoid the singularity by going into orbit around it, but they could never move outward again from any particular orbit.