The Essential Cosmic Perspective, 8e (Bennett et al.)
Chapter 14 The Bizarre Stellar Graveyard
14.1 Multiple Choice Questions
1) Degeneracy pressure stops the crush of gravity in all the following except
A) a brown dwarf.
B) a white dwarf.
C) a neutron star.
D) a very massive main-sequence star.
E) the central core of the Sun after hydrogen fusion ceases but before helium fusion begins.
2) A white dwarf is
A) the exposed core of a dead star, supported by electron degeneracy pressure.
B) the exposed core of a dead star, supported by neutron degeneracy pressure.
C) a hot but very small main-sequence star with a mass of less than 1.4 solar masses.
D) a cool and very small main-sequence star with a mass of less than 1.4 solar masses.
E) the name for the singularity at the center of a black hole.
3) A teaspoonful of white dwarf material on Earth would weigh
A) a few grams.
B) a few pounds.
C) a few tons.
D) about the same as Mt. Everest.
E) about the same as the Earth.
4) Which of the following is closest in mass to a typical white dwarf?
A) the Moon
B) the Earth
C) Jupiter
D) the Sun
5) Why is there an upper limit to the mass of a white dwarf?
A) White dwarfs come only from stars with masses less than 1.4 solar masses.
B) The more massive the white dwarf, the greater the degeneracy pressure and the faster the
speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of
light, and no more mass can be supported.
C) The more massive the white dwarf, the higher its temperature and hence the greater its
degeneracy pressure. Near 1.4 solar masses, the temperature becomes so high that all matter
effectively melts into subatomic particles.
D) The upper limit to the masses of white dwarfs was determined through observations of white
dwarfs in binary systems, but no one knows why the limit exists.
6) What is the ultimate fate of an isolated white dwarf?
A) It will cool down and become a cold black dwarf.
B) As gravity overwhelms the electron degeneracy pressure, it will explode as a nova.
C) As gravity overwhelms the electron degeneracy pressure, it will explode as a supernova.
D) As gravity overwhelms the electron degeneracy pressure, it will become a neutron star.
E) The electron degeneracy pressure slowly overwhelms gravity and the white dwarf evaporates.
7) Suppose a white dwarf is gaining mass because of accretion from a binary companion. What
happens if its mass reaches the 1.4 solar mass limit?
A) The white dwarf undergoes a collapse and expels the excess mass in a nova eruption.
B) Temperatures skyrocket to the point where carbon fusion is possible, which leads to a white
dwarf supernova explosion.
C) The white dwarf immediately collapses into a black hole, disappearing from view.
D) A white dwarf can never gain enough mass to reach the limit because a strong stellar wind
prevents the accreting material from reaching it in the first place.
8) Which of the following hypothetical observations would contradict our theories about the
formation and evolution of white dwarfs?
A) discovery of a white dwarf with a mass 1.5 times that of the Sun (1.5 Msun)
B) discovery of a white dwarf with a surface temperature of 6,000 K
C) discovery of a white dwarf at the center of a planetary nebula
D) discovery of a white dwarf with a 1.5 Msun mass main-sequence companion
9) In which wavelength region(s) would we need to carry out observations in order to study the
accretion disk around a white dwarf in a binary system?
A) visible and infrared light
B) infrared and radio light
C) X-ray and ultraviolet light
D) gamma ray and X-ray light
E) radio and visible light
10) Which of the following statements about novae is not true?
A) A star system that undergoes a nova may have another nova sometime in the future.
B) A nova involves fusion taking place on the surface of a white dwarf.
C) Our Sun will probably undergo at least one nova when it becomes a white dwarf about 5
billion years from now.
D) When a star system undergoes a nova, it brightens considerably, but not as much as a star
system undergoing a supernova.
E) The word nova means “new star” and originally referred to stars that suddenly appeared in the
sky, then disappeared again after a few weeks or months.
11) What kind of pressure supports a white dwarf?
A) neutron degeneracy pressure
B) electron degeneracy pressure
C) thermal pressure
D) radiation pressure
E) all of the above
12) What is the upper limit to the mass of a white dwarf?
A) There is no upper limit.
B) There is an upper limit, but we do not yet know what it is.
C) 2 solar masses
D) 1.4 solar masses
E) 1 solar mass
13) Imagine comparing a 1.2 solar mass white dwarf to a 1.0 solar mass white dwarf. Which of
the following must be true?
A) The 1.2 solar mass white dwarf has a larger radius.
B) The 1.2 solar mass white dwarf has a smaller radius.
C) The 1.2 solar mass white dwarf has a higher surface temperature.
D) The 1.2 solar mass white dwarf has a lower surface temperature.
E) The 1.2 solar mass white dwarf is supported by neutron degeneracy pressure; the 1 solar mass
white dwarf is supported by electron degeneracy pressure.
14) Which of the following is closest in size (radius) to a white dwarf?
A) the Earth
B) a small city
C) a football stadium
D) a basketball
E) the Sun
15) What kind of star is most likely to become a white-dwarf supernova?
A) an O star
B) a star like our Sun
C) a binary M star
D) a white dwarf star with a red giant binary companion
E) a pulsar
16) Observationally, how can we tell the difference between a white-dwarf supernova and a
massive-star supernova?
A) A massive-star supernova is brighter than a white-dwarf supernova.
B) A massive-star supernova happens only once, while a white-dwarf supernova can repeat
periodically.
C) The spectrum of a massive-star supernova shows prominent hydrogen lines, while the
spectrum of a white-dwarf supernova does not.
D) The light of a white-dwarf supernova fades steadily, while the light of a massive-star
supernova continues to brighten for many weeks.
E) White-dwarf supernovae are typically white in color, while massive-star supernovae are
typically red.
17) After a massive-star supernova, what is left behind?
A) always a white dwarf
B) always a neutron star
C) always a black hole
D) either a white dwarf or a neutron star
E) either a neutron star or a black hole
18)
This figure shows how the luminosity of supernovae change over time. How long does it take a
white dwarf supernova to decrease in luminosity by a factor of 100 from its peak?
A) about 300 days
B) about 200 days
C) about 100 days
D) about 25 days
19) A paperclip with the density of a neutron star would weigh (on the Earth)
A) about the same as a regular paperclip.
B) a few tons.
C) more than Mt. Everest.
D) more than the Moon.
E) more than the Earth.
20) Which of the following is closest in size (radius) to a neutron star?
A) the Earth
B) a city
C) a football stadium
D) a basketball
E) the Sun
21) Which of the following best describes what would happen if a 1.5 solar mass neutron star,
with a diameter of a few kilometers, were suddenly to appear in your hometown?
A) The entire mass of the Earth would end up as a thin layer, about 1 cm thick, over the surface
of the neutron star.
B) It would rapidly sink to the center of the Earth.
C) The combined mass of the Earth and the neutron star would cause the neutron star to collapse
into a black hole.
D) It would crash through the Earth, creating a large crater, and exit the Earth on the other side.
E) It would crash into the Earth, throwing vast amounts of dust into the atmosphere which in turn
would cool the Earth. Such a scenario is probably what caused the extinction of the dinosaurs.
22) From an observational standpoint, what is a pulsar?
A) a star that slowly changes its brightness, getting dimmer and then brighter, with a period of
anywhere from a few hours to a few weeks
B) an object that emits flashes of light several times per second (or even faster), with near perfect
regularity
C) an object that emits random “pulses” of light, sometimes with only a fraction of a second
between pulses and other times with several days between pulses
D) a star that changes color rapidly, from blue to red and back again
23) From a physical standpoint, what is a pulsar?
A) a star that alternately expands and contracts in size
B) a rapidly rotating neutron star
C) a neutron star or black hole that happens to be in a binary system
D) a binary system that happens to be aligned so that one star periodically eclipses the other
E) a star that is fusing iron in its core
24) What causes the radio pulses of a pulsar?
A) The vibration of the neutron star.
B) As the neutron star spins, beams of radio radiation sweep through space. If one of the beams
crosses the Earth, we observe a pulse.
C) The neutron star undergoes periodic explosions of nuclear fusion that generate radio pulses.
D) The neutron star’s orbiting companion periodically eclipses the radio waves that the neutron
star emits.
E) A black hole near the neutron star absorbs energy and re-emits it as radio waves.
25) How do we know that pulsars must be neutron stars?
A) We have observed massive-star supernovae produce pulsars.
B) Telescopic images of pulsars and neutron stars look exactly the same.
C) No massive object, other than a neutron star, could spin as fast as we observe pulsars to spin
and remain intact.
D) Pulsars have the same upper mass limit as neutron stars do.
E) This is only a theory that has not yet been confirmed by observations.
26) What is the ultimate fate of an isolated pulsar?
A) It will spin ever faster, becoming a millisecond pulsar.
B) As gravity overwhelms the neutron degeneracy pressure, it will explode as a supernova.
C) As gravity overwhelms the neutron degeneracy pressure, it will become a white dwarf.
D) It will spin ever slower, the magnetic field will weaken, and it will cease to be a pulsar.
E) The neutron degeneracy pressure will eventually overwhelm gravity and the pulsar will
slowly evaporate.
27) The surface of the neutron star RXJ2015 has a temperature of 10 million K. This neutron star
emits radiation most strongly in
A) X-ray light.
B) visible light.
C) radio light.
D) infrared light.
28) Which of the following correctly describes how light will be affected as it tries to escape
from a massive object like a neutron star?
A) Light doesn’t have mass; therefore, it is not affected by gravity.
B) The light will be redshifted.
C) The light will be blueshifted.
D) The visible light will be redshifted, but higher frequencies, such as X-rays and gamma rays,
will not be affected.
29) How does a black hole form from a massive star?
A) During a supernova, if the mass of the infalling core has enough gravity to overcome neutron
degeneracy pressure, the core will collapse to a black hole.
B) Any star more massive than 1.4 solar masses will undergo a supernova explosion and leave
behind a black hole remnant.
C) If enough mass is accreted by a white dwarf star that it exceeds the 1.4 solar mass limit, it will
undergo a supernova explosion and leave behind a black-hole remnant.
D) If enough mass is accreted by a neutron star, it will undergo a supernova explosion and leave
behind a black-hole remnant.
E) A black hole forms when two massive main-sequence stars collide.
30) Which of the following statements about black holes is not true?
A) If you watch an object fall into a black hole, you will never see the object cross the event
horizon. However, the object will fade from view as the light it emits becomes more and more
redshifted.
B) If we watch a clock fall toward a black hole, we will see it tick slower and slower.
C) The event horizon of a black hole represents a boundary from which nothing can escape.
D) If the Sun magically disappeared and was replaced by a black hole of the same mass, the
Earth would soon fall into the black hole.
E) If you fell into a supermassive black hole (so that you could survive the tidal forces), you
would experience time to be running normally as you plunged across the event horizon.
31) Consider an X-ray binary system in which the compact object is surrounded by an accretion
disk. All of the following statements about such accretion disks are true except
A) X-rays are emitted by the hot gas in the accretion disk.
B) the accretion disk consists of material that spills off the companion star.
C) the compact object may be either a neutron star or a black hole.
D) several examples of flattened accretion disks being “fed” by a large companion star can be
seen clearly in photos from the Hubble Space Telescope.
E) the radiation from an accretion disk may vary rapidly with time.
32) A 10 solar mass main-sequence star will produce which of the following remnants?
A) white dwarf
B) neutron star
C) black hole
D) none of the above
33) Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit,
what will you notice?
A) Time on the clock will run slower as it approaches the black hole, and light from the clock
will be increasingly redshifted.
B) Time on the clock will run faster as it approaches the black hole, and light from the clock will
be increasingly blueshifted.
C) The clock will fall faster and faster, exceeding the speed of light as it crosses the event
horizon.
D) The clock will fall toward the black hole at a steady rate, so that you’ll see it plunge through
the event horizon within just a few minutes.
34) What event most likely created the atoms of gold found in your jewelry or electronics?
A) a white dwarf supernova
B) a massive star supernova
C) two neutron stars merging
D) two black holes merging
E) the big bang
35) What is the leading hypothesis for the origin of short gamma-ray bursts?
A) new stars forming in the Milky Way
B) supernovae in the Milky Way
C) very powerful supernovae occurring in distant galaxies
D) the collision of stars in the dense nuclei of distant galaxies
E) the collision of two neutron stars or a neutron star with a black hole
36) The first gravitational waves were detected in 2015 by the LIGO observatories in
Washington and Louisiana. What event was thought to cause these gravitational waves?
A) ripples in space-time left over from the Big Bang
B) two neutron stars merging
C) two black holes merging
D) a hypernova
37) If you were to come back to our solar system in 6 billion years, what might you expect to
find?
A) a red giant star
B) a white dwarf
C) a rapidly spinning pulsar
D) a black hole
E) Everything will be essentially the same as it is now.
14.2 True/False Questions
1) Brown dwarfs, white dwarfs, and neutron stars are all kept from collapsing by degeneracy
pressure.
2) The maximum mass for a white dwarf is 1.4 solar masses.
3) More massive white dwarfs are smaller than less massive white dwarfs.
4) There is no upper limit to the mass of a neutron star.
5) The remnant left behind by a white-dwarf supernova is a neutron star.
6) Our Sun will likely undergo a nova event in about 5 billion years.
7) All pulsars are neutron stars, but not all neutron stars are pulsars.
8) Neutron stars are the densest objects that we can directly observe in the universe.
9) No visible light can escape a black hole, but things such as gamma rays, X-rays, and neutrinos
can.
10) Light escaping from white dwarfs will show a gravitational redshift.
11) All massive-star supernovae leave behind black holes as remnants.
14.3 Process of Science Questions
1) “Negatively Defined” Objects: Summarize the best observational evidence that astronomers
have for the existence of stellar mass black holes. Contrast this with the observational evidence
that pulsars exist. Do you agree or disagree with the statement that the best evidence we have for
stellar mass black holes is that we have detected objects for which an alternate explanation is
lacking? How does your answer influence your confidence in the existence of black holes? Does
the strong observational confirmation of Einstein’s general theory of relativity (see Special Topic
General Relativity and Spacetime in Section 14.3) increase your confidence in the existence of
black holes? Should it?
2) Studying the Singularity: The singularity at the center of a black hole is predicted to be a
region of zero volume and infinite density that contains all of the black hole’s mass. It is a point
at which all currently known physical laws break down. Yet in a black hole, this “terrible point”
is hidden from view behind an event horizon that prevents any knowledge about the singularity
reaching the outside universe. Astronomers continue to spend considerable effort trying to
understand the nature of these singularities, objects for which observational input, it would seem,
will be forever lacking. Are these astronomers practicing science? Argue both yes and no. Which
do you find convincing?
3) Evidence that Pulsars are Neutron Stars: Suppose a friend of yours insists that pulsars are
artificial time-signals constructed by aliens. List and explain all of the observational evidence
that pulsars are actually natural phenomena, namely rapidly spinning neutron stars.
4) The coolest white-dwarf: Surveys have been carried out to identify isolated white-dwarfs
throughout the galaxy and its globular clusters. They have been found to span a range of
temperatures, with a sharp lower limit of about 3,000 K (i.e., many have been found at all
temperatures from 10s of thousands of Kelvin down to 3,000 K, but none cooler). What does this
observation reveal about the age of our galaxy?
14.4 Short Answer Questions
1) Could our Sun ever undergo a nova or a white-dwarf supernova event? Why or why not?
2) Why does the size of a white dwarf decrease with increasing mass?
3) Briefly describe how a nova event occurs.
4) Why do white-dwarf supernovae all have the same maximum luminosity?
5) What is an X-ray burster? What causes the X-ray bursts?
6) What would happen if a small piece of neutron star material (say the size of a paper clip)
struck the Earth?
7) Suppose you find an X-ray binary system that shows X-ray bursts. Is it possible that this
system consists of a red giant and a black hole? Why or why not?
8) Briefly describe what you would see if your friend plunged into a black hole.
9) Why would the earth’s orbit be unaffected were the Sun to suddenly become a black hole?
10) What is the evidence that gamma-ray bursts originate from beyond the Milky Way Galaxy?
11) Explain why black holes in binary systems are associated with strong, steady X-ray emission.
14.5 Mastering Astronomy Reading Quiz
1) A white dwarf is ________.
A) what most stars become when they die
B) a precursor to a black hole
C) an early stage of a neutron star
D) a brown dwarf that has exhausted its fuel for nuclear fusion
2) A typical white dwarf is ________.
A) about as massive as the Sun but only about as large in size as Earth
B) as large in diameter as the Sun but only about as massive as Earth
C) about the same size and mass as the Sun but much hotter
D) as massive as the Sun but only about as large in size as Jupiter
3) If you had something the size of a sugar cube that was made of white dwarf matter, on Earth it
would weigh ________.
A) as much as a large vehicle
B) about 5 pounds
C) as much as Mt. Everest
D) as much as an average person
4) The mass limit of a white dwarf was calculated by
A) Subrahmanyan Chandrasekhar, a 19 year old from India, on a boat ride to England.
B) Albert Einstein, using his general theory of relativity.
C) Sir Arthur Eddington, the famous English astronomer.
D) Robert Oppenheimer, the physicist who led the Manhattan Project to develop the atomic
bomb.
5) What is an accretion disk?
A) a disk of hot gas swirling rapidly around a compact object
B) any flattened disk in space, such as the disk of the Milky Way Galaxy
C) a stream of gas flowing from one star to its binary companion star
D) a disk of material found around every white dwarf in the Milky Way Galaxy
6) According to our modern understanding, what is a nova?
A) an explosion on the surface of a white dwarf in a close binary system
B) the explosion of a massive star at the end of its life
C) the sudden formation of a new star in the sky
D) a rapidly spinning neutron star
7) Suppose that a white dwarf is gaining mass through accretion in a binary system. What
happens if the mass someday reaches the 1.4 solar mass limit?
A) The white dwarf will explode completely as a white dwarf supernova.
B) The white dwarf will collapse in size, becoming a neutron star.
C) The white dwarf will undergo a nova explosion.
D) The white dwarf will collapse to become a black hole.
8) A neutron star is ________.
A) the core remnant of a star that died in a massive star supernova
B) the remains of a star that died by expelling its outer layers in a planetary nebula
C) a star made mostly of elements with high atomic mass numbers, so that they have lots of
neutrons
D) an object that will ultimately become a black hole
9) A typical neutron star is more massive than our Sun and about the size (radius) of ________.
A) a small asteroid (10 km in diameter)
B) Earth
C) the Moon
D) Jupiter
10) If you had something the size of a sugar cube that was made of neutron star matter, on Earth
it would weigh ________.
A) about as much as a large mountain
B) about 50 pounds
C) as much as the entire Earth
D) about as much as a large vehicle
11) Pulsars have powerful magnetic fields because
A) they contain many free electrons in their interiors.
B) the magnetic field lines of the original star’s core were compressed into the neutron star.
C) they are extremely small and compact.
D) they have very active accretion disks.
12) How is an X-ray burst (in an X-ray binary system) similar to a nova?
A) Both involve explosions on the surface of a stellar corpse.
B) Both typically recur every few hours to every few days.
C) Both are thought to involve fusion of hydrogen into helium.
D) Both result in the complete destruction of their host stars.
13) What is the basic definition of a black hole?
A) an object with gravity so strong that not even light can escape
B) a dead star that has faded from view
C) any object made from dark matter
D) an object that absorbs all light and emits radiation based only on its temperature
14) Based on current understanding, the minimum mass of a black hole that forms during a
massive star supernova is roughly ________.
A) 0.5 solar masses
B) 1.4 solar masses
C) 3 solar masses
D) 10 solar masses
15) What do we mean by the event horizon of a black hole?
A) It is the boundary beyond which light cannot escape.
B) It is the very center of the black hole.
C) It is the distance from the black hole at which stable orbits are possible.
D) It is the place where X-rays are emitted from black holes.
16) Imagine that our Sun were magically and suddenly replaced by a black hole of the same
mass (1 solar mass). What would happen to Earth in its orbit?
A) Earth would almost instantly be sucked into oblivion in the black hole.
B) Earth would orbit faster, but at the same distance.
C) Earth would slowly spiral inward until it settled into an orbit about the size of Mercury’s
current orbit.
D) Nothing; Earth’s orbit would remain the same.
17) What do we mean by the singularity of a black hole?
A) It is the center of the black hole, a place of infinite density where the known laws of physics
cannot describe the conditions.
B) It is the “point of no return” of the black hole; anything closer than this point will not be able
to escape the gravitational force of the black hole.
C) It is the edge of the black hole, where one could leave the observable universe.
D) The term is intended to emphasize the fact that an object can become a black hole only once,
and a black hole cannot evolve into anything else.
18) Why do astronomers think the star system Cygnus X-1 contains a black hole?
A) It emits X-rays characteristic of an accretion disk, and the unseen object in the system is too
massive to be a neutron star.
B) No light is emitted from this star system, so it must contain a black hole.
C) The fact that we see strong X-ray emission tells us that the system must contain a black hole.
D) Cygnus X-1 is a powerful X-ray burster, so it must contain a black hole.
19) The Schwarzschild radius of a black hole depends on ________.
A) only the mass of the black hole
B) the observationally measured radius of the black hole
C) the way in which the black hole formed
D) both the mass and density of the black hole
20) Based on current evidence, which of the following statements about gamma-ray bursts is
true?
A) All the bursts that we have detected occurred in distant galaxies.
B) They come primarily from the Milky Way’s central black hole.
C) They occur in the same types of close binary systems that produce X-ray bursts.
D) All gamma-ray bursts are produced by supernovae.
21) Which of the following statements about electron degeneracy pressure and neutron
degeneracy pressure is true?
A) Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron
degeneracy pressure is the main source of pressure in neutron stars.
B) Both electron degeneracy pressure and neutron degeneracy pressure help govern the internal
structure of a main-sequence star.
C) The life of a white dwarf is an ongoing battle between electron degeneracy pressure and
neutron degeneracy pressure.
D) In a black hole, the pressure coming from neutron degeneracy pressure is slightly greater than
that coming from electron degeneracy pressure.
14.6 Mastering Astronomy Concept Quiz
1) Which of the following statements about degeneracy pressure is not true?
A) Degeneracy pressure can continue to support an object against gravitational collapse even if
the object becomes extremely cold.
B) Degeneracy pressure arises from a quantum mechanical effect that we don’t notice in our
daily lives.
C) Black holes form when gravity overcomes neutron degeneracy pressure.
D) Degeneracy pressure can arise only from interactions among electrons.
2) The more massive a white dwarf, the ________.
A) smaller its radius
B) higher its temperature
C) larger its radius
D) higher its luminosity
3) Which of the following best describes why a white dwarf cannot have a mass greater than the
1.4-solar-mass limit?
A) Electron degeneracy pressure depends on the speeds of electrons, which approach the speed
of light as a white dwarf’s mass approaches the 1.4-solar-mass limit.
B) White dwarfs get hotter with increasing mass, and above the 1.4-solar-mass limit they would
be so hot that even their electrons would melt.
C) White dwarfs are made only from stars that have masses less than the 1.4-solar-mass limit.
D) The upper limit to a white dwarf’s mass is something we have learned from observations, but
no one knows why this limit exists.
4) The white dwarf that remains when our Sun dies will be mostly made of ________.
A) hydrogen
B) helium
C) carbon
D) neutrons
5) Which statement about accretion disks is not true?
A) The primary factor determining whether a white dwarf has an accretion disk is the white
dwarf’s mass.
B) The gas in the inner parts of the disk travels faster than the gas in the outer parts of the disk.
C) The gas in the inner parts of the disk is hotter than the gas in the outer parts of the disk.
D) Accretion disks are made primarily of hydrogen and helium gas.
6) What triggers a nova explosion in a white dwarf system?
A) Hydrogen gas from a companion star builds up on the surface of the white dwarf and, when
the temperature gets high enough, it fuses to helium.
B) Carbon fusion begins in the core of a white dwarf.
C) Hydrogen fusion begins in the core of a white dwarf.
D) The white dwarf gains enough mass to exceed the 1.4-solar-mass limit.
7) Which of the following is not true about differences between novae and supernovae?
A) Supernovae eject gas into space, but novae do not.
B) Novae are much less luminous than supernovae.
C) Novae occur only in binary star systems, while supernovae can occur both among single stars
and among binary star systems.
D) The same star can undergo novae explosions more than once, but can undergo only a single
supernova.
8) Will our Sun ever undergo a white dwarf supernova explosion? Why or why not?
A) No, because it is not orbited by another star.
B) Yes, right at the end of its double-shell burning stage of life.
C) Yes, when it becomes a white dwarf.
D) No, because the Sun’s core will never be hot enough to fuse carbon and other heavier
elements into iron.
9) What caused the rapid spin of a neutron star that we see as a pulsar?
A) the force of the supernova explosion that formed the neutron star
B) the magnetic field that was compressed into the neutron star as it formed
C) the conservation of angular momentum during the collapse of the original star’s core
D) Astronomers do not know why pulsars spin so rapidly.
10) Each Voyager spacecraft carries a “postcard” designed to be understandable to any aliens that
might someday encounter it. On the “postcard,” scientists pinpointed the location of Earth by
triangulating it between pulsars. Why did the scientists choose pulsars rather than some other
type of star?
A) Pulsars are easy to identify by their almost perfectly steady periods of pulsation.
B) Pulsars are very bright and therefore easy to find.
C) Several pulsars are located within a dozen light-years of our solar system, making them useful
for finding our solar system.
D) We’re pretty sure that aliens will have only radio telescopes and not optical telescopes, so
they’ll have a better chance of seeing pulsars than ordinary stars.
11) Which statement about pulsars is not thought to be true?
A) Pulsars can form only in close binary systems.
B) All pulsars are neutron stars, but not all neutron stars are pulsars.
C) A pulsar must have a very strong magnetic field and rotate quite rapidly.
D) Pulsars are kept from collapsing by neutron degeneracy pressure.
12) How does an accretion disk around a neutron star differ from an accretion disk around a
white dwarf?
A) The accretion disk around a neutron star is much hotter and emits higher-energy radiation.
B) The accretion disk around a neutron star is made mostly of helium while the accretion disk
around a white dwarf is made mostly of hydrogen.
C) The accretion disk around a neutron star is more likely to give birth to planets.
D) The accretion disk around a neutron star always contains much more mass.
13) Which statement concerning black hole masses and Schwarzschild radii is not true?
A) In a binary system with a black hole, the Schwarzschild radius depends on the distance from
the black hole to the companion star.
B) The more massive the black hole, the larger the Schwarzschild radius.
C) Even an object as small as you could become a black hole if there were some way to
compress you to a size smaller than your Schwarzschild radius.
D) For black holes produced in massive star supernovae, Schwarzschild radii are typically a few
to a few tens of kilometers.
14) Which two theories disagree when it comes to describing the singularity thought to be at the
center of a black hole?
A) Newton’s law of gravity and Einstein’s general theory of relativity
B) Newton’s law of gravity and quantum physics
C) Newton’s third law of motion and Einstein’s general theory of relativity
D) quantum physics and Einstein’s general theory of relativity
15) Which of the statements below about black holes is not true?
A) A spaceship passing a few million kilometers from a 10 solar mass black hole is much more
likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar
mass main-sequence star.
B) Although we are not 100% certain that black holes exist, we have strong observational
evidence in favor of their existence.
C) If you watch an object fall into a black hole, you will never see it cross the event horizon;
you’ll only see it fade from view as the light it emits or reflects becomes more and more
redshifted.
D) If you fell into a black hole, you would experience time to be running normally as you
plunged rapidly across the event horizon (assuming you could survive that long).
16) When we see X-rays from an accretion disk in a binary system, we can’t immediately tell
whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe
each of the following phenomena in this system. Which one would rule out the possibility of a
black hole?
A) intense X-ray bursts
B) spectral lines from the companion star that alternately shift to shorter and longer wavelengths
C) visible and ultraviolet light from the companion star
D) bright X-ray emission that varies on a time scale of a few hours
17) Which of the following observatories is most likely to discover a black hole in a binary
system?
A) the Chandra X-Ray Observatory
B) the Hubble Space Telescope
C) the SOFIA airborne infrared observatory
D) the Arecibo Radio Observatory
18) Which of the following statements about gamma-ray bursts is not true?
A) Based on their distribution in the sky, we can rule out a connection between gamma-ray
bursts and X-ray binaries in the Milky Way Galaxy.
B) Gamma-ray bursts are among the most luminous events that ever occur in the universe.
C) The events responsible for gamma-ray bursts apparently produce only gamma rays, and no
other light that we can hope to detect.
D) Gamma-ray bursts were originally discovered by satellites designed to look for signs of
nuclear bomb tests on Earth.
19) Suppose a science fiction movie depicted a civilization living on a planet orbiting a close
binary star system that consists of a red giant star and a black hole. Why is this an extremely
unlikely scenario?
A) The star that created the black hole would have been very hot, making it very unlikely that
life would have been able to develop due to the ultraviolet light emitted by the star.
B) The supernova explosion that created the black hole would have destroyed any life on a
nearby planet.
C) The star that created the black hole would have been very massive and short lived; making it
very unlikely that life would have had time to develop on a nearby planet before the star went
supernova.
D) all of the above
20) Suppose you were unfortunate enough to fall into a black hole in a binary system where the
black hole was accreting matter from its companion star. Which of the following is most likely to
kill you first?
A) X-rays from the accretion disk
B) tidal forces due to the black hole
C) the crush of gravity at the singularity embedded within the black hole
D) the sucking force from the black hole, which will cause your head to explode
21) Imagine what would happen if Jupiter was suddenly replaced by a black hole with the same
mass as Jupiter.
A) The orbits of the other planets in the solar system would be unaffected.
B) The other planets would slowly be pulled into Jupiter, but the Sun would be unaffected.
C) The other planets and the Sun would slowly be pulled into Jupiter.
D) The entire solar system would instantly be sucked into the black hole.