Ch.15 Verified Test Bank Black Holes Matters of Gravity - Discovering the Universe 14e Test Bank + Answers by Neil F. Comins. DOCX document preview.
Chapter 15: Black Holes: Matters of Gravity
Section: 15-1
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. 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
10. 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
11. 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.
12. 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
13. 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.
14. 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
15. 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
16. 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.
17. 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.
18. 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.
19. 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.
20. 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.
Section: 15-2
21. 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.
22. What property of matter does general relativity address that is NOT included in special relativity?
A) acceleration
B) color
C) mass
D) temperature
23. 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.
24. 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
25. 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
26. 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.
27. 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.
28. 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
29. 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.
30. 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
31. 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
32. 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.
33. 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.
Section: 15-3
34. 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
35. 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.
36. 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) light on the surface of the planet. For an H 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
37. A massive blue-white supergiant star emits the Hα wavelength from its surface, as does a much less-massive red dwarf star. Will these wavelengths differ when one sees them? If so, how?
A) The light from the more massive star will have the shorter wavelength.
B) The light from the less massive star will have the shorter wavelength.
C) Both wavelengths will appear the same, and this will also match the wavelength of an Hα source on Earth.
D) Both wavelengths will appear the same, but both will be longer than the wavelength from an Hα source on Earth.
38. 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.
39. 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
40. 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.
41. 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.
42. 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.
43. 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.
44. 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
45. 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.
Section: 15-4
46. 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.
47. 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.
48. 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.
49. 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
50. 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.
51. 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.
52. 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.
53. 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
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.
55. 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.
56. 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.
57. 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.
58. 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.
59. 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.
60. 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
61. 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.
62. 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
63. 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
64. 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
Section: 15-5
65. What separates a black hole from the rest of the universe?
A) crystalline crust
B) surface of the ergoregion
C) singularity
D) event horizon
66. 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
67. 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
68. 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.
69. 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.
70. 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
71. 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
72. 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
73. 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
74. 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.
75. 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
76. 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
77. 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.
78. 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
79. 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.
80. 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.
81. 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
82. What happens to the magnetic field of a star that collapses completely to become a black hole?
A) The magnetic field becomes infinitely intensified.
B) The magnetic field must be radiated away; black holes never have magnetic fields.
C) The magnetic field becomes compressed and intensified by a factor equal to the ratio of the star’s original diameter to the diameter of the event horizon.
D) The magnetic field becomes weaker by the ratio of the diameter of the black hole event horizon to the star’s original diameter.
83. In general, how many fundamentally different types of black holes are expected to exist?
A) only one—all properties but mass are destroyed when a black hole is created
B) two—those that have electric charge and those that have no electric charge
C) three—atomic-mass black holes, stellar-mass black holes, and supermassive black holes
D) two—those that rotate and those that do not rotate
84. Primordial black holes can have masses from a few grams to the mass of a planet. What would be the radius of a primordial black hole with a mass of 10 grams?
A) about 5 10–36 m; less than the Planck length!
B) about 0.9 10–15 m; the charge radius of a proton
C) about 3 10–15 m; the classical radius of the electron
D) about 5 10–11 m; the radius of the lowest electron orbit in hydrogen
85. What is a Schwarzschild black hole?
A) supermassive black hole
B) uncharged black hole
C) black hole that fills its Schwarzschild radius with matter
D) nonrotating black hole
86. What name is given to a nonrotating black hole?
A) wormhole
B) Hawking singularity
C) Schwarzschild black hole
D) Kerr black hole
87. What name is given to a rotating black hole?
A) Schwarzschild black hole
B) Hawking singularity
C) wormhole
D) Kerr black hole
88. What is a Kerr black hole?
A) nonrotating black hole
B) rotating black hole
C) uncharged black hole
D) hypothetical zero-mass black hole
89. How do Kerr black holes differ from Schwarzschild black holes?
A) Kerr black holes have infinite mass; Schwarzschild black holes do not.
B) Kerr black holes have net electric charge; Schwarzschild black holes do not.
C) Kerr black holes have accretion disks; Schwarzschild black holes do not.
D) Kerr black holes rotate; Schwarzschild black holes do not.
90. The difference between a Schwarzschild black hole (SBH) and a Kerr black hole (KBH) is
A) overall mass; an SBH contains about 20 solar masses, whereas a KBH is greater than 20 solar masses.
B) that the KBH is electrically charged, whereas the SBH is not.
C) that an SBH is spinning, whereas a KBH is not.
D) that a KBH is spinning, whereas an SBH is not.
91. What is the ergoregion of a Kerr black hole?
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
92. In the context of black holes, the word “ergosphere” names the
A) entire region inside the event horizon.
B) region just outside the event horizon of a rotating black hole where it is impossible for anything to remain at rest.
C) entire universe outside the black hole.
D) region occupied by the accretion disk where matter from a companion star collects around a black hole.
93. One day, while straying dangerously close to a black hole, an astronaut notices that no matter how hard he tries to remain at rest, he is inevitably drawn into the black hole unless he keeps moving. What does this tell an observer about the black hole?
A) The black hole is evaporating.
B) The black hole is supermassive.
C) The black hole is electrically charged.
D) The black hole is rotating.
94. What is located in the exact center of a Kerr (rotating) black hole?
A) nothing
B) the singularity
C) the event horizon
D) the ergoregion
95. 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
A) the conservation of energy.
B) the principle of equivalence.
C) Kepler’s third law.
D) the conservation of angular momentum.
96. What is the Schwarzschild radius of a 2-solar-mass black hole?
A) 60 km
B) 6000 km
C) 6 m
D) 6 km
97. What happens to the Schwarzschild radius of a black hole if one doubles the amount of mass in the black hole?
A) The Schwarzschild radius is doubled.
B) The Schwarzschild radius is halved.
C) The Schwarzschild radius decreases by a factor of 4.
D) The Schwarzschild radius is quadrupled (4 times).
98. How does the diameter of a black hole (size of the event horizon) depend on the mass inside the black hole?
A) The diameter does not depend on the mass.
B) The greater the mass, the greater is the diameter—until the mass becomes relatively large and then the diameter decreases with increasing mass.
C) The greater the mass, the greater is the diameter.
D) The greater the mass, the smaller is the diameter.
99. Suppose the Sun became a 1-solar-mass Schwarzschild black hole. What would be its Schwarzschild radius?
A) 2 10–8 au
B) 7 10–3 au
C) 5 au
D) 3000 au
100. The age of the universe is roughly 15 billion years, which is also the approximate evaporation time for a black hole with a mass of 1010 kg. What is the Schwarzschild radius of such a black hole?
A) 5.0 10–21 meters
B) 1.5 10–17 meters
C) 6.3 10–4 meters
D) 1.5 au
101. The supermassive black hole candidate in the center of the galaxy NGC 4261 is estimated to have a mass of 1.2 109 MSun. What is the Schwarzschild radius of this black hole?
A) 1.6 109 meters, a little larger than the Sun
B) 24 au, a little larger than Jupiter’s orbit
C) 0.95 pc, more than half the distance to the nearest star
D) 1600 pc, about one-tenth of the way across the Milky Way Galaxy
102. What is the distance from the center to the event horizon of a nonrotating black hole with the mass of Earth?
A) 8.5 10–7 m
B) 9 mm
C) 1.5 m
D) 6 km
Section: 15-6
103. 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?
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.
104. 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)?
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.
105. What would happen to the gravitational force on Earth if the Sun were to be replaced by a 1-solar-mass black hole?
A) The gravitational force on Earth would become extremely high, sufficient to pull Earth into the black hole.
B) The gravitational force on Earth would double in strength.
C) The gravitational force on Earth would remain as it is now.
D) The gravitational force on Earth would be much less because the gravitational field of a black hole exists only very close to it.
106. If the Sun were replaced by a 1-solar-mass black hole, then Earth would
A) enter an elliptical orbit passing close to the black hole, with its farthest distance from the black hole equal to 1 au.
B) spiral quickly into the black hole.
C) head off into interstellar space along a straight-line tangent to its original orbit around the Sun.
D) continue to orbit the black hole in its present orbit.
107. Suppose it were possible to lower a yellow sodium lamp toward the event horizon of a black hole. What would an observer see while watching from a safe distance?
A) The brightness and color would each remain unchanged.
B) The light from the lamp would change to orange and then red.
C) The light would remain yellow, but there would be fewer and fewer photons being emitted from it.
D) The light from the lamp would change to green and then blue.
108. As an observer is investigating a black hole from a safe distance, a rivet pops out of the tailfin on their spaceship and falls toward the black hole. Will the observer ever see the rivet enter the event horizon?
A) Yes. However, it will be so blueshifted that the observer would need X-ray eyes to see it.
B) No. It will be compressed to zero size and disappear from sight before it reaches the event horizon.
C) Yes. The observer will see it fall faster and faster until it disappears as it falls through the event horizon.
D) No. It will appear to stop and hover forever before entering the event horizon.
109. A laborer repairing the clock tower on a space station orbiting a black hole accidentally drops the clock in such a way that it accelerates toward the black hole. What does the worker see while watching the clock?
A) The hands of the clock keep normal time since time is absolute and the same everywhere.
B) The hands of the clock move slower and slower until they and the clock itself stop at the event horizon.
C) As the clock nears the event horizon, the hands begin to move randomly as time becomes jumbled near the black hole.
D) The hands of the clock move faster and faster until the clock plunges through the event horizon.
110. What appears to happen to a clock as it approaches and reaches the event horizon around a black hole when viewed by a remote observer?
A) Time appears to pass at a much faster rate, becoming infinitely fast at the event horizon.
B) Time appears to slow down and stop.
C) Time speeds up because of the intensified gravitational field.
D) Time ticks uniformly since nothing changes the progress of time.
111. If a person falls as far as the event horizon of a black hole, what would happen to the person’s heart rate, as perceived by a distant observer (apart from the effects caused by the person’s adrenaline level)?
A) The heart rate would appear to have slowed down somewhat, but not much, because of the change of the speed of light in the gravity field.
B) The heart rate would appear to be zero; his heart would appear to have stopped.
C) The heart rate would appear to have speeded up to an incredible rate.
D) The heart rate would appear to be normal since gravity has no effect on time intervals.
112. An astronaut tosses a green ball toward a Schwarzschild black hole. Which of these will NOT be observed as the ball accelerates toward the event horizon?
A) The ball will appear green, then yellow, then red.
B) The ball will become elongated.
C) The ball’s lateral size will decrease.
D) The ball will spin faster and faster.
113. In the context of black holes, what is a wormhole?
A) “tunnel” of undistorted space through an event horizon allowing objects to enter and leave a black hole without being torn apart
B) direct connection from any black hole to another part of spacetime
C) small, black hole through a solid object such as a planet
D) direct connection from a rotating black hole to another part of spacetime
114. Which of these statements correctly describes “cosmic censorship”?
A) Black holes cannot have magnetic fields.
B) All properties of the matter inside a black hole are hidden by the event horizon, except for the total mass of the matter.
C) The amount of mass in a black hole can never be measured.
D) Nothing can leave a local region of space that contains a singularity.
115. A light wave is emitted from the accretion disk surrounding a black hole and moves toward the hole and away from an observer. This observer will see
A) the beam of light moving faster than c as it accelerates toward the hole.
B) the beam of light slow down and stop as it reaches the event horizon.
C) that the wavelength of the light is gravitationally blueshifted and Doppler redshifted, and the two effects just cancel as the light reaches the event horizon.
D) that the wavelength of the light is gravitationally blueshifted as it falls toward the event horizon.
116. The existence of gravitational waves was first suggested observationally by measurements of
A) a binary pulsar.
B) a black hole merger.
C) Type II supernovae.
D) gamma-ray bursts.
117. When they merge, black holes release a burst of gravitational waves. What is the energy source for these waves?
A) Hawking radiation
B) the accompanying supernova
C) the black hole orbits
D) the accretion disk
118. Gravitational waves are
A) instabilities generating cosmic rays.
B) ripples in the fabric of spacetime.
C) structures on the event horizon of a black hole.
D) tidal forces that elongate objects falling into black holes.
119. The first direct gravitational waves to be directly observed were produced by
A) a binary pulsar.
B) a black hole merger.
C) Type II supernovae.
D) gamma-ray bursts.
120. For typical gravitational waves generated by black hole mergers, how large is the distortion on a rod 1 meter long?
A) 10-20 m
B) 10-10 m
C) 10-5 m
D) 10-2 m
121. Why do astronomers seek to measure gravitational waves simultaneously with at least three detectors?
A) in order to measure their amplitude
B) because the waves evolve as they pass through Earth
C) because the waves have wavelengths much larger than Earth
D) in order to pinpoint the direction of their source
Section: 15-7
122. The accretion disk surrounding a black hole is characterized by the emission of
A) red light.
B) blue light.
C) radio waves.
D) X-rays.
123. Which effects have been useful (and successful) in the search for and identification of black holes in the universe?
A) influence of their intense gravitational field on atoms that are emitting light from the event horizons of the black holes
B) their gravitational influence on nearby matter, particularly companion stars
C) effect of their angular momentum, or spin, on nearby matter
D) their magnetic fields and the influence of these fields on nearby matter
124. Matter in an accretion disk is in orbit around a black hole, but friction within the disk causes the matter to gradually spiral into the black hole. What will change in terms of the observable properties of the black hole as this process continues?
A) Only the mass will increase.
B) The mass, the angular momentum, and the rate of evaporation of the black hole will increase.
C) Nothing will change.
D) Both the mass and the angular momentum of the black hole will increase.
125. What mechanism in the vicinity of a star gives astronomers a hint of the presence of a black hole as a companion to the star?
A) The light from the companion star shows extreme redshift because of the gravitational field of the black hole.
B) The star periodically disappears from the viewpoint of Earth during its eclipses by the black hole as the two objects orbit each other.
C) The space near the star darkens, indicating that the black hole prevents the light from distant objects from reaching Earth.
D) Gas from the star, falling in toward a black hole, is compressed to very high densities and temperatures so that it emits an intense and rapidly fluctuating flux of X-rays.
126. Which of these techniques has been successful in identifying good candidates for a black hole in the Milky Way Galaxy?
A) detection of extremely redshifted starlight from a region in the nearby spiral arm of the Galaxy
B) detection of X-rays from a binary star undergoing mass exchange, where masses of component stars can be determined
C) detection of an extremely dark point in the sky from which no light at all is seen
D) gravitational lensing of light from a distant object by the black hole to produce two identical images
127. 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?
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
128. Supposedly nothing can escape from a black hole, yet astronomers are locating black hole candidates by the X-rays they emit. How can X-rays be coming from a black hole?
A) The X-rays come from a highly compressed region in an accretion disk outside the event horizon of the black hole.
B) X-rays are not light or matter and can therefore escape from inside the black hole.
C) If the black hole is rotating, it modifies spacetime around it so much that particles and X-rays are created in the vacuum just outside the event horizon.
D) The X-rays are produced by vibrations of the black hole itself and therefore do not come from inside the black hole.
129. X-rays that come from the vicinity of a black hole actually originate from
A) just outside the event horizon, on the accretion disk.
B) the exact center, or singularity, of the black hole.
C) relatively far away from the black hole, where matter is quite cool.
D) well inside the event horizon.
130. A compact body pulls material from a binary companion. This material plunges toward the compact body and emits X-rays. Which of these phenomena would this description NOT fit?
A) pulsating X-ray source
B) X-ray burster
C) black hole in a binary system
D) nova
131. If a black hole is truly black and the escape velocity associated with it is greater than the speed of light such that no light can escape it, where do the X-rays from the black hole candidates so far identified originate?
A) The black hole is only black to visible radiation, but X-rays travel faster than the speed of light and so can escape.
B) The X-rays originate from the normal star accompanying the black hole; its ordinary light is blueshifted into the X-ray spectral region by the intense gravity of the black hole.
C) The X-rays originate from stars behind the black hole, the light from which is focused and concentrated such that it becomes X-ray radiation by gravitational focusing.
D) The X-rays originate from the matter surrounding the black hole that is highly condensed and hence very hot because of the intense gravitational field.
132. The intense X-rays emitted by a suspected black hole are generated by what physical mechanism?
A) blueshifting of light emitted by hot gas into the X-ray region of the electromagnetic spectrum by the extreme speed of the gas moving into the black hole
B) induced emission in atoms by the intense gravitational field as material moves toward the black hole
C) compressional heating as material moves into the black hole
D) deceleration of matter as it abruptly stops at the event horizon of the black hole
133. In principle, if astronomers were in the vicinity of a Schwarzschild black hole, how could they measure its mass?
A) Put a satellite in orbit around it and measure its period.
B) Measure the gravitational redshift from its radiation.
C) Use charged particles to measure the strength of its magnetic field.
D) Measure the speed necessary to pass through the ergoregions and emerge.
134. Gas can be pulled off a binary companion by a black hole. The black hole’s event horizon is too small to allow all the gas to enter perpendicularly, so it orbits in a ring around the black hole or a neutron star. What is this ring called?
A) gas ring
B) Kerr disk
C) accretion disk
D) ergoregion
135. How has the diameter of the black hole candidate Cygnus X-1 been estimated?
A) from the angular size in the sky of Cygnus X-1 and its known distance from Earth
B) from the time scale of the flickering of the X-rays Cygnus X-1 emits
C) from the orbital period around a companion star of Cygnus X-1
D) from the length of time Cygnus X-1 blocks off the light from its companion star when Cygnus X-1 passes in front of (eclipses) its companion, as seen from Earth
136. The X-ray source Cygnus X-1 is a black hole candidate located in a binary star system. The X-ray source is believed to occupy a volume smaller than Earth. This size is deduced from
A) rapid flickering in the X-ray brightness of Cygnus X-1.
B) Cygnus X-1’s apparent magnitude and distance.
C) Cygnus X-1’s luminosity and spectral class.
D) the shortness of Cygnus X-1’s orbital period.
137. One object that is believed to be a black hole in the Milky Way Galaxy is the
A) central star in the Crab Nebula.
B) central star in the planetary nebula the Ring Nebula in Lyra.
C) Vela pulsar.
D) powerful X-ray source Cygnus X-1.
138. How was the black hole candidate Cygnus X-1 first discovered?
A) by extremely high spatial resolution radio observations with the VLA radio interferometric array in New Mexico
B) by high-resolution visible-light observations with the Hubble Space Telescope
C) by X-ray measurements with the Uhuru satellite
D) by infrared observations with the IRAS infrared satellite
139. How has the mass of the black hole candidate Cygnus X-1 been estimated?
A) from the periodic wobble it produces in the spectral lines of a normal companion star around which it orbits
B) from the gravitational redshift, where the more massive the object, the greater the redshift of its spectral lines
C) from the observed size and estimated density of the object
D) from the periodic wobble in its own characteristic black-hole spectrum
140. Why is Cygnus X-1 thought to be a black hole?
A) Cygnus X-1 emits X-rays that flicker on timescales of 1/100 second, a unique characteristic of a black hole.
B) No light has ever been observed to come from Cygnus X-1.
C) Cygnus X-1 is smaller than Earth, but its mass is too large to be a neutron star or white dwarf.
D) Cygnus X-1 has pulled matter from its companion star into an accretion disk around itself.
141. What is believed to be the solar mass of the black hole candidate Cygnus X-1?
A) 120
B) 60
C) 15
D) 1
142. The X-ray source and black hole candidate LMC X-3 has a diameter of 60 km. What is the flicker frequency of its X-ray emission?
A) 2 10–5 s
B) 0.2 ms
C) 1.56 s
D) about 1 day
Section: 15-8
143. What is believed to be the solar mass of the black hole candidate at the center of the galaxy M87?
A) 3 million
B) 3 billion
C) 300,000
D) 300
144. The black hole at the center of the galaxy M87 is estimated to have a mass of 3 109 MSun. Suppose the orbits of the stars observed circling it have semimajor axes of 50 au. Approximately what would be the period of their orbital motion?
A) 3 seconds
B) 24 days
C) 7 years
D) 127 years
145. How was the mass of the candidate black hole at the center of the galaxy M87 estimated?
A) from the amount of mass that is disappearing into it every year
B) from the periodic shift in the wavelengths of spectral lines from a companion object around which the black hole is orbiting
C) from observations of the very high orbital speed of objects close to this center
D) from the intensity of X-rays emitted from it and the frequency of the flickering of the X-ray intensity
146. Where should an astronomer look for a supermassive black hole?
A) in the center of a galaxy
B) at the center of the universe
C) orbiting a normal star in the Milky Way Galaxy
D) at the center of a supernova remnant
147. By what method are MOST intermediate black holes thought to have formed?
A) collapse of a supermassive star
B) collisions between stars in crowded environments
C) direct collapse of a gas cloud in the early universe
D) during the Big Bang
148. The formation of supermassive black holes
A) occurred only during the Big Bang.
B) began during the early era that saw the formation of galaxies.
C) occurred at the instant dark energy became dominant in the universe.
D) only occurs in globular clusters.
149. What is a primordial black hole?
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
150. What name is given to any black hole that might have been created in the Big Bang at the beginning of the universe?
A) supermassive black hole
B) Schwarzschild black hole
C) Kerr black hole
D) primordial black hole
151. Theoretical physics predicts various types of black holes. Which of these is NOT one of them?
A) primordial black holes: masses from a few grams to the mass of a planet
B) intermediate mass black holes: hundreds to thousands of solar masses
C) supermassive black holes: millions or billions of solar masses
D) supercluster black holes: billions of billions of solar masses
Section: 15-9
152. Gas jets have often formed perpendicular to the plane of the accretion disk around a black hole or a neutron star. What propels the gas away from the hole or star?
A) magnetic forces from the object’s strong magnetic field
B) conservation of momentum since the outgoing particles are pair-produced as virtual particles near the object
C) enormous pressure of the compressed infalling gas of the accretion disk
D) strong curvature of spacetime near the object
153. Suppose an astronomer detects an object that displays jets of material shooting out of opposite sides. This object is probably NOT
A) a solitary black hole with a mass of 10–100 solar masses.
B) a black hole in a binary system.
C) a neutron star in a binary system.
D) a supermassive black hole.
154. 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?
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.
155. One prominent feature recently identified within many energetic close binary star systems as a result of their mutual interaction and mass exchange is
A) two oppositely directed high-speed jets of matter leaving the system.
B) planetary formation between the stars, emitting IR radiation from molecular constituents and dust.
C) the beginnings of spiral arms, showing the possible origin of spiral galaxies.
D) a cool dust cloud surrounding the whole star system, hiding it from visible view.
156. Some objects in the Milky Way Galaxy are observed to be emitting two oppositely directed jets of material. These gas jets are believed to be
A) energetic, charged particles ejected along the magnetic axes of a rotating white dwarf.
B) material squirted out along the rotation axis of an accretion disk around a neutron star or black hole in a binary star system.
C) material transferred onto the surface of a white dwarf star in a binary star system, then subsequently blasted into space by runaway thermonuclear fusion reactions.
D) material expelled from the far side of the companion star in a binary system, repelled by magnetic interaction with the pulsar.
Section: 15-10
157. What is a virtual particle?
A) particle whose existence is too short for observers to know it ever existed
B) particle that never does anything wrong
C) particle that, if it comes in contact with ordinary matter, annihilates to form pure energy
D) particle, like a photon or a graviton, that is made up of waves
158. Sometimes particle-antiparticle pairs are created and then annihilate so quickly that observers cannot know that they ever existed. What are these particles (or antiparticles) called?
A) relativistic particles
B) temporary particles
C) field particles
D) virtual particles
159. If nothing can ever leave a black hole, can the mass of a black hole ever decrease?
A) No.
B) Yes, if antiparticles enter a black hole and annihilate with matter already inside the black hole.
C) Yes, if the matter inside the black hole is radioactive (e.g., uranium), allowing their decay products—alpha particles, electrons, and gamma rays—to constantly leave the black hole.
D) Yes, if particle-antiparticle pairs are created outside the event horizon out of gravitational energy from the black hole and one particle enters the event horizon while the other escapes.
160. 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?
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
161. When particle-antiparticle pairs are created just outside the event horizon of a black hole, one member can escape while the other enters the black hole. What is the name of this stream of particles leaving a black hole?
A) Schwarzschild radiation
B) Kerr radiation
C) Planck radiation
D) Hawking radiation
162. What is Hawking radiation?
A) microwaves from the edge of the visible universe
B) electromagnetic radiation from electrons spiraling in the magnetosphere of a neutron star
C) stream of particles and antiparticles from just outside the event horizon of a black hole
D) X-rays from an accretion disk around a black hole
163. What would the mass of a primordial black hole need to have been for it to be just disappearing now due to the loss of Hawking radiation?
A) 10 kg
B) 10 million kg
C) 10,000 kg
D) 10 billion kg
164. Which one of these statements about the evaporation of black holes is correct?
A) The rate at which a black hole evaporates is lower for a higher-mass black hole.
B) The rate at which a black hole evaporates is higher for a higher-mass black hole.
C) Black holes do not evaporate.
D) The rate at which a black hole evaporates is independent of the mass of the black hole.
165. Suppose a virtual particle-antiparticle pair appears just outside the event horizon of a black hole, and that each particle is the same distance from the center of the black hole. What will happen in this case?
A) Gravity from the black hole will attract the particle and repel the antiparticle, thus separating them. They will become real, and neither of them needs to enter the black hole.
B) Gravity from the black hole will attract the particle and repel the antiparticle, thus separating them. They will become real, and both of them will enter the black hole.
C) Gravity from the black hole will attract the particle and repel the antiparticle, thus separating them. They will become real, and the particle will enter the black hole.
D) The gravitational force from the black hole will cause the particles to move toward each other, and they will recombine without affecting the black hole.
Section: 15-11
166. Which of these statements does NOT correctly compares gamma-ray bursts with X-ray bursts?
A) Gamma-ray bursts occur only once. X-ray bursts can repeat.
B) Gamma-ray bursts originate all over the sky. X-ray bursts come mostly from the galactic plane.
C) In general, gamma-ray bursts carry less energy than X-ray bursts.
D) Gamma-ray bursts appear to originate at the beginning of a supernova explosion. X-ray bursts originate in binary systems.
167. Gamma-ray bursts are at great distances from Earth, yet Earth receives tremendous amounts of energy from them. Explain.
A) Gamma-ray bursts are supermassive stars, equivalent to 100,000 ordinary supernovae.
B) A gamma-ray burst represents the explosion of an entire galaxy.
C) The energy is released along jets rather than uniformly in all directions. If Earth is in the path of one of these jets, a gamma-ray burst is observed.
D) The gamma radiation from a burst is released in all directions, but then it is focused in the direction of Earth by gravitational lensing.
168. What is the observed distribution of the longer-living gamma-ray bursts in the sky?
A) concentrated primarily along the plane of the Milky Way, indicating an origin in the Galaxy
B) uniform over the entire sky, indicating an origin outside of the Milky Way
C) clumpy but not coinciding with any known galaxy clusters, indicating an origin in a new kind of astronomical object
D) clumpy, approximately coinciding with large clusters of galaxies such as the Coma cluster
169. What is the observed distribution of the shorter-living gamma-ray bursts in the sky?
A) concentrated primarily along the plane of the Milky Way, indicating an origin in the Galaxy
B) uniform over the entire sky, indicating an origin outside the Milky Way
C) clumpy but not coinciding with any known galaxy clusters, indicating an origin in a new kind of astronomical object
D) clumpy, approximately coinciding with large clusters of galaxies such as the Coma cluster
170. Efforts to relate gamma-ray bursts with specific sources has had what results so far?
A) Gamma-ray bursts always occur in the depths of space, far from any galactic or other obvious source.
B) Gamma-ray bursts, including those observed in the Milky Way Galaxy, always occur in the centers of galaxies.
C) Gamma-ray bursts appear to occur in galaxies but not at the centers of galaxies.
D) Gamma-ray bursts occur in globular clusters, well away from the main regions in the host galaxy.
171. What is the typical duration of a “long” gamma-ray burst?
A) several days, indicating a size much smaller than the distance from Earth to the nearest star beyond the Sun
B) about a minute, indicating a source smaller than Mercury’s orbit
C) up to about 1 hour, indicating a source less than half the size of the solar system
D) several hours, indicating a source somewhat larger than the solar system
172. What property of the longer-living gamma-ray bursts indicates that they are located at large (“cosmological”) distances from Earth?
A) highly redshifted emission lines seen in their visible spectrum from the burst’s nucleus
B) small apparent sizes of the objects producing the bursts
C) absorption lines in the visible spectra of their remnant glow, due to intergalactic clouds between them and Earth
D) faintness of these bursts
173. Evidence for the conclusion that the longer-living gamma-ray bursts are very distant comes from the
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.
174. How much energy does a typical longer-living gamma-ray burst emit in 100 seconds?
A) as much as the Sun in 100 years
B) as much as the Sun in a month
C) as much as the Sun since the demise of the dinosaurs
D) as much as the Sun over its entire lifetime
175. Particularly powerful supernovae called “hypernovae” occur in
A) supermassive black holes.
B) neutron stars.
C) Wolf-Rayet stars.
D) hyperspace.
176. Which of these is NOT associated with the merger of two neutron stars?
A) Short gamma-ray burst
B) X-ray burster
C) kilonova
D) gravitational radiation
177. Which of these has been associated with a magnetar?
A) short gamma-ray burst
B) long gamma-ray burst
C) ultralong gamma-ray burst
D) All of these have been associated with magnetars.
178. Which of these sources sometimes has an afterglow visible at optical and radio wavelengths?
A) gamma-ray burst
B) pulsar
C) coronal mass ejection
D) nova
179. Which of these has NOT been identified as the progenitor of at least some gamma-ray bursts?
A) magnetar
B) a collision of two neutron stars
C) Wolf-Rayet star
D) a collision of two black holes