1. The explosion of a supernova appears to leave behind
A.a rapidly expanding shell of gas and a central neutron star.
B.a rapidly rotating shell of gas, dust, and radiation but no central object.
C.a rapidly expanding shell of gas and a compact white dwarf star at its center.
D.nothing; the explosion changes all the matter completely into energy that then radiates into space at the speed of light.


2. The Crab Nebula is
A.a supernova remnant.
B.a planetary nebula surrounding a hot star.
C.the active nucleus of a spiral galaxy.
D.a cool prestellar gaseous nebula.


3. A pulsar is most probably formed
A.in the core of a star as it evolves through its main sequence phase.
B.in the center of a supernova explosion.
C.within a huge gas cloud, by collisions between stars.
D.just after the formation of a protostar by gravitational condensation.


4. The pulsation periods of most pulsars are in the range
A.of 1/1000 second and a few seconds.
B.of 10-6 and 10-3 second.
C.from minutes to hours.
D.from many hours to a few days.


5. Which of the following descriptions does NOT represent a property of neutron stars?
A.emitters of relatively narrow beams of radio energy and other electromagnetic radiation
B.rotation rates from one to thirty times each second
C.strong gravitational fields but weak magnetic fields
D.composed almost entirely of neutrons


6. The source of the beams of electromagnetic radiation (including light in some cases) emitted by pulsars is
A.the surface of a normal star that has a white dwarf companion. The white dwarf creates a hot spot on the normal star that emits a beam of light as the stars rotate around each other.
B.charged particles spiraling along the magnetic axes of rotating neutron stars and, because they are being accelerated, emitting electromagnetic radiation.
C.jets of material flowing out along the rotation axis of the accretion disk around a black hole, collisions in the jets heating the material to produce electromagnetic radiation.
D.electrons flowing out along the rotation axis of an accretion disk around a neutron star, the electrons emitting light because they are being accelerated.


7. Some pulsars are found outside the gaseous remnant of the supernova explosion in which they were born. What is believed to be the reason for this?
A.The supernova explosion was asymmetrical, and ejected gas in only one broad direction.
B.The supernova explosion was asymmetrical and gave a strong "kick" to the pulsar.
C.The gaseous remnant is more massive than the neutron star and lags behind it as the galaxy rotates.
D.Galactic rotation creates a "wind" of interstellar gas that pushes on the gaseous remnant but leaves the neutron star unaffected.


8. The main reason for the observed slowdown of Crab pulsar is
A.the slow expansion and redistribution of mass, similar to a spinning skater who spreads her arms outward.
B.a slow buildup of the magnetic field as rotational energy is transferred to magnetic energy.
C.the loss of rotational energy through the emission of beams of charged particles.
D.friction between the stellar surface and the surrounding nebular material.


9. The interior of a neutron star is believed to consist of
A.almost entirely neutrons, but with some protons, electrons, and some nuclei in the innermost part.
B.an inner part with entirely neutrons and an outer part with a mixture of neutrons and neutron-rich nuclei.
C.entirely neutrons.
D.almost entirely neutrons, but with some protons and electrons.


10. The pulsation rate of the pulsar within the Vela supernova remnant has increased abruptly several times since its discovery (see Fig. 23-8, Freedman and Kaufmann, Universe, 6th ed.). What is the presently accepted explanation for this speed-up?
A.The pulsar is a rotating neutron star that is occasionally spun up by the interaction of its powerful magnetic field with passing stars.
B.The pulsar is a rotating neutron star whose surface slows down because of energy loss to radiation, but whose superfluid interior continues to rotate. Friction between these surfaces occasionally spins up the crust.
C.The pulsar is a pulsating white dwarf that occasionally undergoes an abrupt change in its oscillating mode.
D.The pulsar is a rotating neutron star with a solid, rotationally flattened crust. As the pulsar's rotation slows down, the crust readjusts through a "starquake" that causes the pulsar to spin up slightly.


11. The Black Widow pulsar is unusual because it appears to
A.be a solitary millisecond pulsar with no companion star.
B.be eating away at its companion star.
C.have been eaten away by its companion star.
D.be a black hole surrounded by the remnants of its former companion star.


12. Pulsating X-ray sources with periods of a few seconds are caused by
A.the pulsation in radius, temperature, and hence luminosity of a hot Cepheid variable star with a surface temperature hot enough to emit X rays.
B.the eclipsing of an X-ray-emitting star with a very hot surface by a cool companion in a close binary system.
C.matter falling onto the surface of a very hot, rotating white dwarf star from an ordinary companion star in a binary system, producing an X-ray-emitting hot spot that disappears periodically behind the white dwarf.
D.matter falling violently onto the surface of a rotating neutron star from a close companion in a binary star system, causing an X-ray hot spot that disappears periodically behind the neutron star.


13. The nova phenomenon, an occasional and sometimes repeated intense brightening of a star by a factor of about 106, is caused by
A.the beam of radiation from a nearby pulsar illuminating the surface of a red giant star and inducing rapid and intense heating.
B.hydrogen "burning" explosively on the surface of a white dwarf star after mass transfer from a companion star in a binary system.
C.the capture and rapid compression of matter by a black hole.
D.the explosion of a single massive star at the end of its thermonuclear burning phases.


14. X-ray bursters are objects in the sky that emit sudden bursts of X rays in addition to a steady, low-level, X-ray emission. These bursts of X rays are believed to be caused by
A.material transferred onto the surface of a neutron star in a binary system, then subsequently ignited in a thermonuclear explosion that leaves the neutron star intact to repeat the process.
B.material from a companion star pulled into an accretion disk around a black hole, with periodic clumps of material falling from the disk into the black hole to produce the X rays.
C.material transferred onto the surface of a neutron star, causing the neutron star to collapse suddenly into a black hole.
D.material transferred onto the surface of a white dwarf in a binary star system, producing a thermonuclear explosion at the surface while leaving the white dwarf intact to repeat the process.


15. Which statement best describes the "fabric" of space and time as outlined by the classical physics of Newton?
A.Space is expanding uniformly, whereas the rate of passage of time is slowing down as the universe ages.
B.Space becomes "curved" and time slows down near a source of gravity, as measured by a distant observer.
C.The shape of space and the rate of time variation depends on the relative velocities of observer and observed.
D.Space is perfectly uniform and is mapped by a fixed network, whereas time passes at a uniform rate for all observers.


16. What is "special" about the special theory of relativity?
A.It deals only with objects that are at rest relative to one other.
B.It deals only with objects moving in a straight line at constant speed.
C.It deals only with motion at speeds significantly less than the speed of light.
D.It deals with motion at constant velocity and accelerated motion but excludes all other effects; in particular, it excludes gravity.


17. Two rocket ships are traveling past the Earth at 90% of the speed of light in opposite directions (i.e., they are approaching each other). One turns on a searchlight beam, which is seen by scientists aboard the second spaceship. What speed do the scientists measure for this light? (c = speed of light in a vacuum)
A.1.8 c (equal to 2 × 0.9 c)
B.0.9 c
C.1.9 c (equal to c + 0.9 c)
D.c


18. If you see an object moving past you at 90% of the speed of light, you will measure the length of this object to be
A.unchanged from when it is at rest.
B.shorter than if it were at rest while it is traveling toward you, longer than if it were at rest when it is traveling away from you.
C.shorter than if it were at rest.
D.longer than if it were at rest.


19. A child on a playground swing is swinging back and forth (one complete oscillation) once every four seconds, as seen by her father standing next to the swing. At the same time, a spaceship hurtles by at a speed close to the speed of light. According to special relativity (and ignoring the Doppler effect for this question), a person 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 longer than 4 seconds when it is moving away.
B.more than 4 seconds.
C.equal to 4 seconds.
D.less than 4 seconds.


20. In what way is the general theory of relativity more general (deals with more situations) than the special theory?
A.It includes accelerated motion but not gravitation.
B.It includes accelerated motion and gravitation.
C.It includes only constant, unaccelerated motion.
D.It includes only motion at the speed of light.


21. According to Einstein's theory of general relativity, if you watch a clock from a distant location as it is moved closer to a source of gravity, you will see the clock
A.slow down.
B.run faster.
C.only change its rate if it is moving rapidly but maintain its standard rate if stationary in a gravity field.
D.maintain the same rate, because time is unaffected by gravity.


22. What happens to the wavelength of light as it travels outward through the gravitational field of a planet, a star, or other massive object?
A.It stays the same but the intensity of the light decreases.
B.It stays the same but the energy of each photon decreases.
C.It decreases.
D.It increases.


23. Einstein's principle of equivalence in his general theory of relativity asserts that
A.the behavior of all types of atoms in a gravitational field is equivalent.
B.all objects are attracted toward all other objects in the universe by gravitational forces.
C.being at rest in a gravitational field is equivalent to being in an upwardly accelerated frame of reference in a gravity-free environment.
D.if person B is in a rapidly moving reference frame (moving at constant velocity), then person B will observe exactly the same effects for person A as person A observes for person B.


24. According to Newton's law of gravity, why does the Earth orbit the Sun?
A.Matter contains quarks, and the Earth and Sun attract each other with the "color force" between their quarks.
B.Space around the Sun is curved.
C.The Earth and the Sun are continually exchanging photons of light in a way that holds the Earth in orbit.
D.The Sun exerts a gravitational force on the Earth across empty space.


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


26. Which of the following is NOT a test of general relativity but rather a test of special relativity?
A.Light travels in a curved path in a gravitational field.
B.The wavelength of light increases as it leaves a region of gravitational field.
C.The length of a moving object decreases when observed by a stationary observer.
D.The perihelion position of Mercury precesses more quickly than is predicted by Newtonian theory.


27. A black hole is so named because
A.the gravitational field is so high that the wavelength of its emitted light is shifted into the infrared and radio regions of the spectrum.
B.it emits no visible light because it is so cold, its energy being held in an intense gravity field.
C.its spectrum has the same shape as that of a laboratory blackbody at a temperature of about 1000 K.
D.no light can escape from it on account of its powerful gravitational field.


28. What prevents a neutron star from collapsing and becoming a black hole?
A.Gravity in the neutron star is balanced by an outward force due to neutron degeneracy.
B.Neutron stars are held up by the centrifugal force due to their rapid rotation.
C.Neutron stars are solid, and like other solid spheres they are held up by the repulsive force between atoms in the solid.
D.Gravity in the neutron star is balanced by an outward force due to gas pressure, as in the Sun.


29. What method is used by astronomers to infer the existence in space of a dark object with a mass of about 5 solar masses such as a black hole?
A.The measurement of the effect of its gravitational force on a companion object in a binary system.
B.The measurement of the gravitational redshift of spectral lines in the spectrum of the object.
C.The estimation of the luminosity of the object and the application of the mass-luminosity relationship.
D.The photography or imaging of a region from which no light or radiation at all appears to come.


30. Which of the following techniques have been successful in identifying good candidates for black holes in our galaxy?
A.detection of X rays from binary stars undergoing mass exchange, where the masses of component stars have been determined
B.detection of extremely redshifted starlight from regions in the nearby spiral arm of the galaxy
C.detection of extremely dark points in the sky, from which no light at all is seen
D.gravitational lensing of light from stars to produce two very close and identical images


31. If a black hole is truly black and has an escape velocity greater than the speed of light such that no light can escape it, where do the X rays come from in the black hole candidates so far identified?
A.from stars behind the black hole, whose light is focused and concentrated by gravitational focusing to the point where it becomes X-ray radiation.
B.The black hole is only black to visible radiation traveling at the speed of light, but because X rays travel faster than the speed of light, they can escape.
C.from the normal star accompanying the black hole, its ordinary light being blueshifted into the X-ray spectral region by the intense gravity of the black hole.
D.from the matter surrounding the black hole, which is highly condensed and hence very hot because of the intense gravitational field.


32. The existence of supermassive black holes in the centers of many galaxies has been inferred by what definitive measurement?
A.the measurement of extremely dark regions of space in the centers of galaxies, from which no radiation is seen
B.measurement of very rapid orbital motion of objects around a very massive central object
C.bending of light from stars on the far sides of galaxies by a very massive central object, as seen from Earth
D.detection of very specific electromagnetic emissions predicted by theory to be emitted by a massive black hole


33. What name is given to any black hole that was created in the Big Bang (the creation of the universe)?
A.supermassive black hole
B.original black hole
C.primordial black hole
D.primeval black hole


34. What is the event horizon of a black hole?
A.the "surface" from the inside of which nothing can escape
B.the "surface" at which all "events" or activity appear to happen because of general relativity
C.the infinitesimally small volume at the center of the black hole that contains all of the black hole's mass
D.the "surface" inside which any object entering will leave with greater energy than that with which it entered


35. The words "Schwarzschild radius" refer to
A.the distance to which gas is ejected in a planetary nebula.
B.half the diameter of a neutron star.
C.half the diameter of the singularity in a black hole.
D.the distance from the center of a black hole at which the escape velocity becomes equal to the speed of light.


36. In reference to black holes, a singularity is
A.the name given to a hot-spot emitting X rays just beyond the event horizon
B.a place just outside the event horizon of a rotating black hole, where it is impossible to remain at rest
C.a place where a non-zero mass occupies zero volume.
D.a place where the escape velocity equals the speed of light


37. Which of the following statements correctly describes "cosmic censorship"?
A.It is not possible to measure both the mass and the electric charge of a black hole with unlimited precision; if our knowledge of one increases, then our knowledge of the other decreases.
B.The only way into or out of a singularity is through an event horizon.
C.Black holes cannot have magnetic fields.
D.It is not possible to measure any property of a black hole other than its mass, its electric charge, and its spin.


38. What happens to the magnetic field of a star that collapses to become a black hole?
A.The magnetic field is radiated away; black holes can never have magnetic fields.
B.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.
C.The magnetic field becomes infinite.
D.The magnetic field becomes weaker by a factor equal to the ratio of the star's original diameter to the diameter of the event horizon.


39. One day, while straying dangerously close to a black hole, you notice that you must keep your spaceship moving; no matter how hard you try to remain at rest you are inevitably drawn into the black hole unless you keep moving. What does this tell you about this specific black hole (other than that it is something that you should leave)?
A.It is rotating.
B.It is a naked singularity.
C.It has an off-axis magnetic field.
D.It is electrically charged.


40. 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 axis of the beam pointing toward the black hole. What happens to the beam as it approaches the event horizon?
A.It begins to rotate faster and faster.
B.It is stretched in length.
C.Nothing happens to its length or rotation; it simply falls faster and faster.
D.It is compressed in length.



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