Astronomy Final Exam
The dimensions of the disk of the Milky Way Galaxy are diameter _____, thickness _____.
100,000 ly; 2000 ly
Does the halo of the Milky Way Galaxy include other galaxies?
Yes. The halo region includes several small galaxies, among them the Magellanic Clouds, two small, irregular galaxies.
Recent observations seem to indicate that, rather than being a spiral galaxy, the Milky Way may be
a barred spiral with a definite, straight bar across its center.
Which of the following components of the Milky Way Galaxy outlines the spiral arms of the Galaxy?
young O and B stars, dust, and gas
What evidence now exists for a supermassive black hole at the center of the Milky Way Galaxy?
very rapid motion of matter close to the nucleus of the Galaxy, requiring a very massive body to hold it in orbit
We have observed the central region of the Milky Way Galaxy in a number of wavelength ranges. With which one of the ranges is it most difficult to obtain information?
visible
What is a galactic halo?
spherical distribution of stars and globular clusters centered on a nuclear bulge
The Milky Way is an example of which type of galaxy?
spiral
Which of the following four spectral classifications signifies the coolest stellar surface temperature? A) B B) K C) G D) A
B
Where are protostars most likely to form? A) emission nebulae B) reflection nebulae C) dark nebulae D) planetary nebulae
C
Which of the following properties is NOT a characteristic of T Tauri stars? A) variations in brightness B) rjection of mass into space C) nuclear reactions in the core D) emission lines in the spectrum
C
Which of the following sentences does NOT state a property of neutron stars? A) Neutron stars rotate from 1 to 30 times per second. B) Neutron stars emit relatively narrow beams of light and other radiation. C) Neutron stars contain strong gravitational fields but weak magnetic fields. D) Neutron stars are composed almost entirely of neutrons.
C
The stars in the Milky Way Galaxy
move generally around the galactic center.
The spiral-arm structure of the Milky Way Galaxy has been measured and evaluated most effectively by observations of
21-cm radiation from interstellar hydrogen and the distribution of young stars.
A brown dwarf is a(n) A) object intermediate between a planet and a star, with not enough mass to begin nuclear reactions in its core. B) general name for an object similar to the planet Jupiter. C) star whose blackbody spectrum peaks in the brown region of the visible spectrum. D) star of less than about 1.5 solar masses at the very end of its life, after it has cooled to near invisibility.
A
A pulsar is a(n) A) rapidly spinning neutron star. B) type of variable star, pulsating rapidly in size and brightness. C) very precise interstellar beacon perhaps operated by intelligent life forms. D) accretion disk around a black hole, emitting light as matter is accumulated on the disk.
A
A star ascending the red-giant branch for the second time in the asymptotic giant branch phase will have A) no nuclear reactions in the core, but a helium-fusion shell outside the core, which itself is surrounded by a shell of hydrogen. B) no fusion reactions; the star has used up all its nuclear fuel. C) hydrogen-fusion reactions occurring in the core. D) no nuclear reactions occurring in the core but hydrogen fusion in a shell outside the core.
A
A typical white dwarf has a surface temperature about four times that of the Sun and a radius about 1% that of the Sun. What can you determine about the luminosity of a typical white dwarf from this information? A) The white dwarf will be less luminous than the Sun. B) The white dwarf and the Sun will have about the same luminosity. C) The white dwarf will be more luminous than the Sun. D) Nothing can be concluded about the relative luminosities from this information.
A
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.
A
Which of the following statements does NOT describe a consequence of core collapse at the end of the life of a massive star? A) The silicon core is converted to iron by fusion reactions. B) Electrons combine with protons to form neutrons. C) Great numbers of neutrinos are produced. D) The core density approaches the density of an atomic nucleus.
A
How does a white dwarf generate its energy? A) It no longer generates energy but is slowly cooling as it radiates away its heat. B) Nuclear fusion of hydrogen into helium is producing energy in its core. C) Nuclear fission of heavy elements in the central core is releasing energy. D) Gravitational potential energy is released as the star slowly contracts.
A
How is gas distributed in interstellar space? A) in clumps, concentrated in interstellar clouds B) concentrated in narrow riverlike streams of gas that extend across the Galaxy C) uniformly distributed through space D) concentrated around existing stars because of the stars' gravitational pull
A
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.
A
In which of the following locations would a clock run at its fastest rate? A) empty space B) Earth's surface C) Jupiter's atmosphere D) "weightless" environment on the Space Shuttle in orbit around Earth
A
Luminosity is measured in A) watts. C) watts per square meter. B) watts per second. D) parsecs.
A
Planetary nebulae are so named because A) they were extended objects, often green-colored, that looked like planets when first seen by nineteenth-century observers through their telescopes. B) the ejected material is rich in carbon and oxygen, necessary elements for the manufacture of planets in the nebulae surrounding stars. C) they rotate slowly and condense into planetary objects around a central star. D) their spectra appear to be similar to the spectra of the giant gas planets in the solar system.
A
Protostars are A) very young objects still contracting before becoming true stars. B) old stars contracting after using up all of their available hydrogen fuel. C) objects with less than about 0.08 solar mass that do not have enough mass to become true stars. D) stars made almost entirely out of protons.
A
The "star" that is seen at the center of a planetary nebula is A) a small, hot, and very dense white dwarf star. B) composed almost entirely of neutrons and spinning rapidly. C) the accretion disk around a black hole. D) a planet in the process of formation
A
The Crab Nebula is A) a supernova remnant. B) a planetary nebula surrounding a hot star. C) a cool, gaseous nebula in which stars are forming. D) the active nucleus of a nearby spiral galaxy.
A
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, which then radiates into space at the speed of light.
A
The stars in an open cluster are useful for studying the early stages of stellar evolution because all the stars in a cluster have the same A) age. B) spectral type. C) luminosity class D) radius.
A
Which of the following statements about the rate of stellar evolution is true? A) The more massive the original star, the faster is the evolution. B) The chemical make-up of the original nebula is the major factor in deciding the rate of evolution, whatever the mass of the star. C) Star mass has no bearing on stellar evolution since all stars evolve at the same rate, controlled by nuclear fusion. D) The more massive the original star, the slower is the evolution since there is more material for thermonuclear burning
A
The structure of the deep interior of a low-mass star near the end of its life is a(n) A) carbon-oxygen core, a shell around the core where helium nuclei are undergoing fusion, and a surrounding shell of hydrogen. B) inactive hydrogen core and a helium shell undergoing nuclear fusion surrounded by a carbon-oxygen shell. C) turbulent mixture of hydrogen, helium, carbon, and oxygen in which only helium continues to undergo nuclear fusion. D) helium core surrounded by a thin hydrogen shell undergoing nuclear fusion with very small concentrations of heavier nuclei.
A
The very strong magnetic field on a neutron star is created by A) the collapse of the star, which significantly intensifies the original weak magnetic field of the star. B) differential rotation of the star, with the equator rotating faster than the poles, similar to sunspot formation. C) a burst of neutrinos produced by the supernova explosion, the equivalent of a very large electrical current flowing for a short time. D) turbulence in the electrical plasmas during the collapse of the star; the original star would have had no magnetic field.
A
Type II supernovae show prominent lines of hydrogen in their spectra, whereas hydrogen lines are absent in spectra of Type Ia supernovae. Explain. (Hint: Think about the type of star that gives rise to each of the two types of supernova.) A) Massive stars contain large amounts of hydrogen, whereas white dwarfs are mostly carbon and oxygen. B) White dwarfs have a thick surface layer of hydrogen, whereas neutron stars contain no hydrogen at all. C) Massive stars have fused all their hydrogen into heavier elements, whereas low-mass stars still have large hydrogen-rich envelopes. D) Massive stars contain large amounts of hydrogen, whereas neutron stars contain no hydrogen at all.
A
What is a cosmic ray shower? A) shower of particles produced when a cosmic ray strikes atoms in Earth's atmosphere B) burst of high-energy atomic nuclei arriving at Earth from interstellar space C) Another name for a meteor shower D) pulse of gamma rays arriving at Earth from a rotating, magnetized neutron star
A
What is a dwarf star? A) main-sequence star B) large, planetary object, such as Jupiter C) star of about the same size (diameter) as Earth D) star that is significantly smaller than a giant or supergiant star
A
What is a protostar? A) sphere of gas after collapse from an interstellar cloud but before nuclear reactions have begun B) small interstellar cloud before it collapses to become a star C) star near the end of its life before it explodes as a supernova D) shell of gas left behind from the explosion of a star as a supernova
A
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) Gravity is balanced in neutron stars by the outward centrifugal force produced by their rapid rotation. C) Gravity in the neutron star is balanced by an outward force due to gas pressure, as in the Sun. D) Neutron stars are solid, and, like any solid sphere, they are held up by the repulsive forces between atoms in the solid matter.
A
Where are the most massive stars to be found in the main sequence of a Hertzsprung-Russell diagram? A) upper left end B) Main-sequence stars all have approximately the same mass, by definition. C) center D) lower right end
A
Which force induces the core to contract inward and get hotter in massive stars at the conclusion of each episode of nuclear fusion, such as the carbon-, oxygen-, and silicon- fusion cycles? A) gravity B) gas pressure produced by the very high gas temperatures C) electron degeneracy pressure D) nuclear attractive force between nuclei and between neutrons and protons
A
Which of the following is a correct and complete statement of Einstein's first postulate of special relativity? A) Your description of physical reality is the same regardless of the constant velocity at which you move. B) Your description of physical reality is the same regardless of the direction in which you move, even if the speed changes. C) Your description of physical reality is the same regardless of how you move. D) Your description of physical reality is the same regardless of the constant speed at which you move, even if direction changes.
A
Which of the following 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.
A
Which of the following mechanisms is thought to be ineffective and inefficient in the triggering of star birth in molecular clouds? A) gravitational contraction of a hot gas cloud B) collisions between two interstellar clouds C) supernova explosions and the resultant shock waves D) radiation pressure from the intense UV radiation from hot stars
A
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.
B
1. Which of the following molecules is likely to be the most common in interstellar space? A) OH, hydroxyl B) H2, molecular hydrogen C) CO, carbon monoxide D) H2O, water
B
A planetary nebula is created A) over several hundred years, during mass transfer in a close binary star system. B) over a few thousand years or more, in a slow expansion away from a low-mass star, driven by a series of thermal pulses from helium fusion. C) in hours or less, during the explosion of a massive star. D) in seconds, during the helium flash in a low-mass star
B
Where would you expect to find a core-collapse supernova? A) in a globular cluster C) in a binary star system B) near a star-forming region D) near a black hole
B
Can a white dwarf explode? A) Yes, but only if another star collides with it; stars are so far apart in space that this is unlikely ever to have happened in our Galaxy. B) Yes, but only if it is in a binary star system. C) Yes, but only if nuclear reactions in the white dwarf core reach the stage of silicon fusion, producing iron. D) No. White dwarfs are held up by electron degeneracy pressure, and this configuration is stable against collapse or explosion.
B
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.
B
Evidence of massive amounts of hydrogen gas surrounding some stars comes from A) observation of the reddening of the spectra of these stars because of absorption of blue light by hydrogen. B) observation of emission of characteristic red Balmer light from nebulosity around them. C) theoretical calculations that correctly describe stellar formation by the gravitational contraction of hydrogen gas. D) observation of the blue glow from scattered light in their reflection nebulae.
B
From observations of supernova explosions in distant galaxies, it is predicted that there should be about five supernovae per century in our Galaxy, whereas we have seen only about one every 300 years from Earth. Explain. A) The majority of supernovae produce no visible light, only radio and X-ray radiation, which we have been able to observe from Earth for only the past three decades. B) Most supernovae occur in the galactic plane, where interstellar dust has hidden them from our view from Earth. C) Most supernovae occur in the Milky Way and can be seen only from the southern hemisphere, where there have been very few observers until recently. D) The majority of stars in the Galaxy are old, well beyond the supernova stage of evolution.
B
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.
B
How must an object be moving for us 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.
B
What would be the mass of a main-sequence star that has a luminosity 1000 times greater than that of the Sun? (See Figure 11-14, Comins and Kaufmann, Discovering the Universe, 8th ed.) A) 105 solar masses B) 5 solar masses C) 0.1 solar mass D) 1000 solar masses
B
If a person falls as far as the event horizon of a black hole, what would happen to the person's heart rate (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.
B
In which order do the stages of core nuclear fusion occur in the evolution of a massive star? A) carbon, helium, oxygen, neon B) helium, carbon, neon, oxygen C) helium, oxygen, carbon, neon D) helium, carbon, oxygen, neon
B
Low-mass stars can undergo two evolutionary phases called red-giant phases. What is the difference between them? A) In the first, the primary production of energy is from hydrogen burning in the core. In the second, the primary production of energy is from helium burning in the core. B) In the first, the primary production of energy is from helium burning in the core. In the second, the primary production of energy is from helium burning in a shell around the core. C) In the first, the star's track on the Hertzsprung-Russell diagram lies along the red- giant branch. In the second, the track lies along the horizontal branch. D) During the first red-giant phase, the star moves up and to the right along the red-giant branch. During the second red-giant phase the star's track is down and to the left along the same red-giant branch.
B
Suppose a satellite were placed in orbit around (and very close to) a neutron star. Which theory would you need to use to describe how it moves? A) special theory of relativity C) Kepler's laws B) general theory of relativity D) Newton's law of gravitation
B
The definition of a main-sequence star is a star A) with a surface temperature equal to that of the Sun. B) in which nuclear fusion reactions generate sufficient energy to oppose further condensation of the star. C) whose age after birth is about 1 million years. D) with a luminosity precisely equal to that of the Sun
B
The pulsed nature of the radiation at all wavelengths that is seen to come from a pulsar is produced by A) the rapid pulsation in size and brightness of a small white dwarf star. B) the rapid rotation of a neutron star that is producing two oppositely directed beams of radiation. C) the mutual eclipses of two very hot stars orbiting in a close binary system. D) extremely hot matter that is rapidly orbiting a black hole just prior to descending into it.
B
Thermonuclear reactions release energy because the product (ash) nucleus A) contains fewer protons than the original (fuel) nucleus since these protons have been converted into energy. B) is more tightly bound than the original (fuel) nucleus. C) is less tightly bound than the original (fuel) nucleus. D) is moving faster than the original (fuel) nucleus, and the excess kinetic energy shows up as heat.
B
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.
B
What is a Kerr black hole? A) nonrotating black hole C) uncharged black hole B) rotating black hole D) hypothetical zero-mass black hole
B
What is a white dwarf star? A) large, planetary object, such as Jupiter B) star of about the same size (diameter) as Earth C) star that is significantly smaller than a giant or supergiant star D) main-sequence star with a surface temperature near 12,000 K
B
What is the ultimate fate of an open star cluster? A) The shape of the cluster will remain more or less as it is at the present time as the stars in it age and die. B) The stars in the cluster escape one by one until the cluster no longer exists. C) Over time the stars collide and merge, eventually creating a black hole. D) The stars gradually sink toward the center, creating a globular cluster.
B
What physical process provides the energy for the ejection of a planetary nebula from a low-mass star? A) transfer of hydrogen-rich material onto the surface of a white dwarf from its companion in a binary star system B) helium shell flashes in the helium fusion shell C) core collapse and the ensuing shock wave D) collision with another star
B
Which of the following mechanisms is NOT considered to be a way in which star formation is triggered or started? A) collisions between interstellar clouds B) heating of an interstellar cloud by radiation from embedded young stars C) compression of an interstellar cloud by the shock waves from supernova explosion D) compression of an interstellar cloud by the pressure of light from nearby stars
B
Which of the following phenomena is never a consequence of a supernova explosion? A) triggering of star formation by shock waves moving through interstellar space B) formation of a planetary nebula C) condensation of matter into a solid nuclear star composed entirely of neutrons D) generation of a pulse of neutrino emission
B
Which type of dwarf is largest? A) white dwarf B) red dwarf C) brown dwarf D) All are about the same size.
B
White dwarfs radiate most strongly in the ultraviolet, with a peak wavelength of perhaps 300 nm. What would be the surface temperature of a white dwarf? A) 12,600 K B) 9700 K C) 7800 K D) 3500 K
B
Why is there a limited range of stellar surface temperatures around 10,000 K at which neutral hydrogen gas absorbs visible light in the Balmer series? A) There must be electrons at the n = 3 energy level for Balmer absorption to occur. If the gas is too cold, electrons are only in the n = 1 and 2 levels; if the gas is too hot, the gas is ionized and no electrons are left in the hydrogen atoms. B) Electrons in hydrogen have to be at the n = 2 energy level to produce absorption in this series. If the gas is too cold, most atoms are in the n = 1 state; if it is too hot, most atoms are ionized. C) Electrons must be in the ground state n = 1 to undergo Balmer absorption. If the gas is too cold, electrons cannot be excited from this level; if the gas is too hot, there are no electrons left in the n = 1 level. D) There must be sufficient continuum radiation from the stellar surface in the visible region to be absorbed by the hydrogen gas.
B
A clock is moving across your line of sight with its face turned toward you. Which of the following statements about this clock, as seen by you, is NOT correct? A) The clock will run slow compared with a clock in your hand. B) The clock will appear shorter than it would if it were at rest. C) The clock will appear thinner, front to back, than it would if it were at rest. D) The clock will appear denser than it would if it were at rest.
C
4. What is the typical mass of a giant molecular cloud? A) 10 to 100 solar masses B) 1000 to 10,000 solar masses C) 100,000 to 1 million solar masses D) 10 million to 1 billion solar masses
C
A Type Ia supernova is the A) collapse of a blue supergiant star to form a black hole. B) explosion of a red giant star as a result of a helium flash in its core. C) explosion of a white dwarf in a binary star system after mass has been transferred onto it from its companion. D) explosion of a massive star after silicon fusion has produced a core of iron nuclei.
C
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.
C
What is a protostar called in the stage after it has finished accreting mass? A) white dwarf B) red giant (or supergiant) C) pre-main-sequence star D) main-sequence star
C
A nova is an explosion involving a white dwarf. Can a white dwarf become a nova more than once? Why or why not? A) No. The white dwarf's magnetic field is eliminated in the explosion. B) Yes. A white dwarf can become a nova more than once if its temperature is high enough for recurrent helium flashes in the core. C) Yes, A white dwarf can become a nova more than once if it continues to receive matter from a companion star. D) No. The white dwarf is destroyed in the explosion.
C
A star of apparent magnitude +1 appears _____ than a star of apparent magnitude +2. A) either brighter or fainter, depending on the distance to the stars B) farther away C) brighter D) fainter
C
A white dwarf star is supported from collapse under gravity by A) pressure of the gas heated by nuclear fusion reactions in its core. B) centrifugal force due to rapid rotation. C) degenerate-electron pressure in the compact interior. D) pressure of the gas heated by nuclear fusion reactions in a shell around its core.
C
A white dwarf star, the surviving core of a low-mass star toward the end of its life, can be found on the Hertzsprung-Russell diagram A) at the upper left end of the main sequence since its surface temperature is extremely high. B) at the bottom end of the main sequence, along which it has evolved throughout its life. C) below and to the left of the main sequence. D) above and to the right of the main sequence since it evolved there after its hydrogen-fusion phase.
C
According to Einstein's general theory of relativity, a clock that ticks at a regular rate far from a source of gravity will appear 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.
C
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
C
At which phase of its evolutionary life is a white dwarf star? A) post-supernova phase, the central remnant of the explosion B) just at main-sequence, or hydrogen-fusion, phase C) very late for small-mass stars, in the dying phase D) in its early phases, soon after formation
C
Compared with a star in the middle of the Hertzsprung-Russell diagram, a star in the lower left of the diagram is A) larger. B) cooler. C) smaller. D) brighter.
C
Compared with a star in the middle of the Hertzsprung-Russell diagram, a star in the upper right of the diagram is A) fainter. B) hotter. C) larger. D) nonexistent because there are no stars that appear in the upper right of the diagram.
C
How far away is the nearest star beyond the Sun? A) about 1/4 ly away C) about 4 ly away B) about 1/10 ly away D) between 1 and 2 ly away
C
If you compare two stars, the one with the _____ must have the greater luminosity. A) larger radius B) higher surface temperature C) smaller absolute magnitude D) larger surface area
C
What is believed to be the maximum mass a star can have? A) about 50 solar masses B) about 1000 solar masses C) about 150 solar masses D) about 500 solar masses
C
In which of the following "frames of reference" would matter behave exactly as it would in a stationary frame of reference? A) accelerating downward in an elevator whose cable has broken B) moving upward against gravity in an elevator as it accelerates from rest C) moving at a constant velocity D) moving at a constant speed in a circular path, such as in an orbit
C
In which region of the Hertzsprung-Russell diagram does a newly formed protostar first appear when it begins to shine at visible wavelengths? A) bottom right corner; very low luminosity because it is both small and cool B) center of the main sequence since all protostars begin their lives at this position and move up or down it depending on their mass as time passes C) right side; relatively large luminosity because of its size but cool D) top left corner; at the top of the main sequence, down which it will progress with time
C
New stars are formed from A) hot supernova remnants. B) activity around black holes in the centers of galaxies. C) huge, cool dust and gas clouds. D) pure energy in free space.
C
The Sun will end its life by becoming a A) molecular cloud. B) black hole. C) white dwarf. D) pulsar.
C
The T Tauri phase of a protostar is characterized by A) the ejection of a planetary nebula. B) strong spectral absorption lines of metals. C) strong spectral emission lines. D) the helium flash.
C
The core collapse phase at the end of the life of a massive star is triggered when A) the helium flash and thermal pulses have expelled the star's envelope. B) the density reaches the threshold for electron degeneracy pressure to become important. C) nuclear fusion has produced a significant amount of iron in its core. D) the core becomes as dense as an atomic nucleus.
C
The escape velocity for material inside a black hole is A) zero. C) greater than the speed of light. B) infinite. D) twice that from a neutron star.
C
The luminosity of a star is A) its brightness as seen by people on Earth. B) its brightness if it were at a distance of 10 pc (32.6 ly) from Earth. C) its total energy output into all space. D) another name for its color or surface temperature.
C
The motion that is used to change the position of the observer in the most common parallax measurements of distances to relatively nearby stars is the A) motion of the Sun around the galactic center. B) change in latitude of the observation point on Earth. C) motion of Earth in its orbit around the Sun. D) rotation of Earth on its axis.
C
The source of a protostar's heat is A) gravitational energy released as the protostar expands. B) nuclear reactions converting helium to carbon and oxygen in its core. C) gravitational energy released as the star contracts. D) nuclear reactions converting hydrogen into helium in its core.
C
The stars that last longest are the stars A) with the largest luminosity and highest temperature since they take the longest to cool down to invisibility. B) with the largest mass, that is, the largest amount of fuel. C) with the smallest mass. D) of intermediate mass; small-mass stars have little fuel and burn out quickly, while very massive stars burn their fuel very rapidly.
C
The statement that the apparent magnitude of a variable star has increased indicates that its A) brightness has increased. B) surface temperature has decreased. C) brightness has decreased. D) surface temperature has increased.
C
What happens to the surface of a low-mass star after the helium core and shell fusion stages are completed? A) The star stabilizes at the size of a red giant star, radiation pressure from below balancing gravity from the core, and slowly cools for the rest of its life. B) The star is spun off into space to make a spiral structure known as a spiral galaxy. C) The star is propelled slowly away from the core to form a planetary nebula. D) The star contracts back onto the core and becomes hot enough to undergo further hydrogen fusion, leading to a very hot and active white dwarf star.
C
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.
D
A main-sequence star can be no smaller than 0.08 solar mass. The reason is that A) thermonuclear reactions begin so suddenly in stars of less than 0.08 solar mass that the star is disrupted by an explosion. B) protostars of less than 0.08 solar mass cannot form. C) protostars of less than 0.08 solar mass are not massive enough to contract. D) the temperature in a contracting protostar of less than 0.08 solar mass does not become high enough for nuclear reactions to start.
D
A white dwarf star, as it evolves, undergoes which of the following changes? A) Its temperature remains constant, but its radius and therefore its luminosity decrease. B) Luminosity and size decrease while its temperature remains constant. C) It shrinks in size, the resulting release of gravitational energy keeping both luminosity and temperature constant. D) Luminosity and temperature decrease while its size remains constant.
D
Accretion of matter in an interstellar cloud leads to A) a supernova explosion since accretion is a nuclear process. B) explosion of this matter when it is attracted to and falls onto the surfaces of stars. C) the formation of molecules from atomic gases. D) a protostar.
D
An astronomer is measuring the brightness of a particular star through a telescope, using different filters in the visual (yellow-green), violet, and ultraviolet regions. What is the name of the technique being used by this astronomer? A) spectroscopy B) geometry C) interferometry D) photometry
D
Apparent magnitude is a measure of a star's A) intrinsic brightness (actual light output). B) size (diameter). C) temperature. D) brightness, as seen from Earth.
D
At the center of the remnant of a Type Ia supernova you would expect to find A) a black hole or neutron star. B) a white dwarf. C) the binary companion of the supernova. D) nothing special.
D
At what stage in its life does a star pass through the protostar phase? A) while it is converting hydrogen into helium in its core B) when it is expanding in size as a red giant or supergiant C) after nuclear reactions end in its core but before the red giant phase D) after condensation but before nuclear reactions begin in its core
D
During its life, a massive star creates heavier and heavier elements in its core through thermonuclear fusion, leading up to silicon and iron. What is the fate of the iron that is created? A) The nuclei are split apart by neutron bombardment, creating lighter elements such as carbon, oxygen, and neon. B) The iron is locked up inside the star forever. C) The iron is destroyed by later thermonuclear fusion reactions in the core that create even heavier elements such as lead, gold, and uranium. D) The iron is torn apart by high-energy photons at the end of the star's life.
D
For Balmer series lines to show up strongly in absorption in stellar spectra, significant numbers of hydrogen atoms have to have electrons in the n = 2 energy level. What then does the appearance of these lines in a stellar spectrum tell us about the temperature of the star's surface? A) The appearance of the lines tells us very little about the temperature because hydrogen gas will show significant Balmer absorption, whatever the surface temperature. B) The temperature must be high enough to ionize the hydrogen atoms by collision in order that they can absorb from this level. C) The temperature must be reasonably low so that no atoms will have electrons excited beyond this energy level (e.g., to n = 3). D) The temperature must be reasonably high to excite the electrons to this level by collisions but not high enough to ionize the atoms.
D
How does the temperature of an interstellar cloud affect its ability to form stars? A) Higher temperatures help star formation. B) Star formation is independent of the temperature of the cloud. C) Star formation is too complicated to be able to say how one quantity, such as temperature, affects it. D) Higher temperatures inhibit star formation.
D
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 you are in front of the tube (electrons approaching you) and a smaller mass if you are standing behind the tube (electrons moving away from you). D) The moving electron appears to have a greater mass.
D
In a star's evolutionary life, the asymptotic giant branch (AGB) is the A) helium core fusion phase. B) pre-main-sequence core hydrogen fusion phase. C) hydrogen shell fusion phase prior to helium ignition in the core. D) helium shell fusion phase.
D
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
D
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
D
In the process of helium shell fusion in a low-mass star near the end of its life, the star moves upward and to the right on the asymptotic giant branch of the Hertzsprung-Russell diagram. In this process, the star is A) contracting, cooling, and hence becoming less luminous. B) expanding, heating up, and becoming more luminous. C) contracting, becoming hotter, and becoming much less luminous. D) expanding, cooling, and becoming more luminous.
D
Just before it exploded, the star that became supernova SN 1987A was a(n) A) pulsar. B) white dwarf. C) M2 I supergiant. D) B3 I supergiant.
D
Long-exposure color photographs of the night sky often show regions that glow red, such as the Rosette Nebula in Figure 12-8 of Comins and Kaufmann, Discovering the Universe, 8th ed. This distinctive red color is caused by the A) emission of red and infrared light by warm dust grains. B) collective glow of many red giant stars in the region. C) scattering of starlight by dust grains in the nebula. D) ionization and subsequent recombination of hydrogen atoms.
D
Neutron stars are believed to be created by A) all types of supernovae. B) type Ia supernovae, i.e., exploding white dwarfs. C) explosions of main-sequence stars. D) type II supernovae, i.e., explosions of high-mass stars.
D
Nuclear fusion reactions of helium produce primarily A) nitrogen and neon nuclei. C) beryllium and lithium nuclei. B) iron nuclei. D) carbon and oxygen nuclei.
D
Stars that have ejected a planetary nebula go on to become A) red giants. B) supernovae. C) protostars. D) white dwarfs.
D
Stellar parallax appears because A) Earth rotates about its own axis. B) stars move in space. C) stars have finite size (i.e., they are not really just points of light). D) Earth moves in space.
D
The Hertzsprung-Russell diagram is a plot of A) apparent brightness against intrinsic brightness of a group of stars. B) apparent brightness against distance for stars near the Sun. C) luminosity against mass of a group of stars. D) absolute magnitude (or intrinsic brightness) against temperature of a group of stars.
D
The chemical makeup of the Sun's surface can be determined by A) taking a sample of the star's surface with a space probe. B) examining the chemicals present in a meteorite because it is part of the solar system. C) measuring the components of the solar wind with Earth-orbiting spacecraft. D) solar spectroscopy.
D
The interior of a neutron star is believed to consist of A) neutrons compressed into a crystalline lattice structure by very high pressure. B) a dense gas consisting mostly of neutrons. C) a metallic fluid of almost pure iron. D) neutrons in a superfluid state.
D
The mass of a particular giant molecular cloud in interstellar space is 2 million solar masses. What is the mass of the helium in this cloud? A) 40,000 solar masses B) 1 million solar masses C) 200,000 solar masses D) 500,000 solar masses
D
The mechanism that gives rise to the phenomenon of the nova is A) the impact and subsequent explosion of a large comet nucleus on a star's surface. B) material falling into a black hole and being condensed to the point where a thermonuclear explosion is produced. C) the complete disintegration of a massive star due to a runaway thermonuclear explosion in the star's interior. D) matter from a companion star falling onto a white dwarf in a close binary system, eventually causing a nuclear explosion on the dwarf's surface.
D
Usually, ideal gases increase their pressure and volume when heated and decrease their pressure and volume when cooled. Do these rules apply to stars? A) No. Stars never follow the rules for ideal gases even approximately. B) Yes. Stars in all stages follow these rules quite closely. C) No Protostars have cores of degenerate matter in which the pressure is independent of the temperature. D) No. White dwarfs are essentially degenerate matter in which the pressure is independent of the temperature.
D
What are the two physical parameters of stars that are plotted in the Hertzsprung-Russell diagram? A) mass and surface temperature B) luminosity and mass C) radius and mass D) luminosity and surface temperature
D
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.
D
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
D
What is believed to be the most important factor determining whether a collapsing region (dense core) in an interstellar cloud becomes a single-star or a multiple-star system? A) fraction of heavy elements in the cloud B) temperature C) mass of the collapsing region D) amount of rotation (spin)
D
What is believed to prevent stars from being larger than a few hundred solar masses? A) Stars of larger mass would collapse under their own gravity and become black holes. B) No interstellar clouds have masses of more than 100 solar masses. C) The cores of larger-mass stars would run through their lives and explode before the stars finish contracting as protostars. D) The temperature becomes so high that the excess mass is pushed back into space by radiation from the star.
D
What is parallax? A) distance to an object, measured in parsecs B) angle taken up by the size (e.g., diameter) of an object, as seen by an observer C) shift in angular position of an object as it moves in space D) apparent shift in position of an object as the observer moves
D
What is the Chandrasekhar limit? A) time limit of the existence of a planetary nebula, beyond which the nebula dissipates and becomes too rarified to see B) time limit for the transfer of mass to a white dwarf in a close binary system, beyond which the white dwarf erupts in a nova C) mass limit to the total mass of a white dwarf, beyond which it will erupt in a nova D) mass limit to the total mass of a white dwarf, beyond which the electron degeneracy pressure will be overcome and the core will collapse
D
What is the characteristic color of a reflection nebula? A) red B) yellow C) green D) blue
D
What is the difference between an extrasolar planet and a sub-brown dwarf? A) There is no difference. These are two different names for the same object. B) A sub-brown dwarf generates a limited amount of energy through fusion of deuterium into helium in its core. An extrasolar planet generates no fusion energy. C) A sub-brown dwarf generates a limited amount of energy through fusion of lithium into helium in its core. An extrasolar planet generates no fusion energy. D) An extrasolar planet orbits a star; a sub-brown dwarf does not. Otherwise, they are the same.
D
What is the event horizon of a black hole? A) "surface" at which any object passing through it will leave with greater energy than 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
D
What point defines the end of the pre-main-sequence phase of a star's life and the start of the main-sequence phase? A) The star begins to expand and become a red giant. B) Convection begins in its interior. C) The star stops accreting mass from the interstellar cloud. D) Nuclear reactions begin in its core.
D
What property separates a black hole from the rest of the universe? A) crystalline crust C) singularity B) surface of the ergoregion D) event horizon
D
What will be the mass of the Sun at the end of its asymptotic giant branch (AGB) phase, due to mass loss to space by its stellar wind? A) still almost 1 solar mass since mass loss is negligible for a low-mass star like the Sun B) between 0.1 and 0.2 solar mass C) about 0.8 solar mass D) about 0.5 solar mass
D
Which of the following common molecules found in interstellar space contains nitrogen atoms but no oxygen? A) water vapor (H2O) B) formaldehyde (H2CO) C) methane (CH4) D) ammonia (NH3)
D
Which of the following facts referring to stars in a cluster is NOT particularly useful for interpreting the evolution of these stars? A) The stars are all at the same distance from the Earth, so we measure true intrinsic brightnesses of the stars. B) The stars all formed at about the same time. C) The stars formed from the same mix of chemical elements but with a mix of original masses. D) The majority of the material in these stars is hydrogen
D
Which of the following important components does a planetary nebula contribute to the interstellar medium? A) molecules such as NH3 and CH4, which contribute to giant molecular clouds B) UV light that photoionizes hydrogen. The hydrogen, on recombination, produces the red Balmer- light by which we see interstellar emission nebulae. C) rotational motion from the original star, which serves to concentrate interstellar matter into new stars and planetary systems D) nuclei of moderately heavy elements, major components of planets such as our own
D
Which of the following spectral classification letters signifies the hottest stellar surface temperature? A) G B) A C) K D) B
D
Which one of the following 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.
D
Which statement best describes the "fabric" of space and time as outlined by the classical physics of Newton? A) Space is expanding uniformly, while time passes more slowly 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 passage of time depend on the relative velocities of observer and observed. D) Space is perfectly uniform, filling everywhere like a fixed network, while time passes at a uniform rate for all observers.
D
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.
D
What is the distribution of giant molecular clouds in the Milky Way Galaxy and other similar galaxies?
Giant molecular clouds occur primarily in the spiral arms
In 1785 William Herschel proposed that the solar system was at the center of the Milky Way Galaxy. How did he reach this conclusion?
Herschel's observations suggested that the stars in the Milky Way Galaxy were distributed uniformly around Earth.
What is the significance of the object Sagittarius A* ("Sagittarius A-star") in the Milky Way Galaxy?
Sagittarius A* appears to be the actual nucleus of the Galaxy.
The component of the Milky Way Galaxy accounts for interstellar extinction, the dimming of light from distant objects is
dust
If the Sun were to be at or close to the galactic center of the Milky Way, the intensity of starlight in the nighttime sky on Earth would be
extremely intense from the dense field of stars, equivalent to about 200 full Moons.
The Milky Way Galaxy appears to have a spiral structure with
four separate major arms.
Where are many of the older, metal-poor stars found in the Milky Way Galaxy?
in globular clusters in the galactic halo
Where in space would you look for a globular cluster?
in the Milky Way galactic halo, orbiting the galactic center in a long elliptical orbit around the galactic center
In the Milky Way Galaxy, young, metal-rich stars are found
in the disk and spiral arms.
Where is the solar system located in the Milky Way Galaxy?
in the galactic disk
The Milky Way Galaxy
is one of many billions of galaxies in the universe.
The possible presence of a supermassive black hole at the center of the Milky Way Galaxy has been deduced from
the very high orbital speed of ionized gas clouds close to the galactic center.
