Astronomy 102 Final Study Guide
For a massive star (e.g., 25 solar masses), core hydrogen fusion lasts for several million years. In contrast, core silicon fusion lasts for only about -1 minute. -several thousand years. -1 day. -1 year.
1 day
A classical Cepheid variable star is seen to vary regularly with a period of 25 days. How many times brighter than the Sun would this star appear to be if it were to replace the Sun in our solar system? -10,000 -4 -1000 -100
10,000
The characteristics of a red supergiant star are the brightness of _____ and a diameter of _____. - 10,000 Suns; about Mars's orbit -about 10,000 Suns; 1/10 that of the Sun -the Sun; Mercury's orbit -about 1 million Suns; the whole solar system
10,000 Suns; about Mars's orbit
The energy output of a bright quasar is equivalent to -1000 Suns. -106 spiral galaxies. -100 bright galaxies. -that of the Milky Way Galaxy.
100 bright galaxies
Compared with the total output of energy from the Milky Way Galaxy, what is the equivalent output of a typical quasar? -about the same energy output -about a million times brighter -only about 1/10 of the Galaxy's output but from a small volume of space -100 times brighter
100 times brighter
The typical diameter of a spiral galaxy is about -1 ly -100,000 ly. -100 ly -10 million ly.
100,000 ly
The dimensions of the disk of the Milky Way Galaxy are diameter _____, thickness _____. -2000 ly; 100,000 ly -28,000 ly; 2000 ly -10,000 ly; 28,000 ly -100,000 ly; 2000 ly
100,000 ly; 2000 ly
When a typical nova explodes, it brightens in a few hours by a factor of -10^8 to 10^10. -10^4 to 10^6 -2 to 5. -10 to 100.
10^4 to 10^6
Which type of radiation has been most effective in evaluating the spiral arm structure of our Galaxy? -Lyman-B ultraviolet emission from hot hydrogen gas -21-cm radio emission from electron "spin-flip" transitions in cool hydrogen gas -synchrotron radiation from electrons spiraling in magnetic fields in the spiral arms -neutrinos from exploding stars in the spiral arms since they can easily penetrate dust and gas
21-cm radio emission from electron "spin-flip" transitions in cool hydrogen gas
The time for the Sun to orbit the galactic center once in its motion in the Milky Way is -about 500,000 years. -2.3 million years. -28,000 years. -230 million years.
230 million years
What is the temperature of the blackbody radiation that we receive from the Big Bang (the cosmic microwave background radiation)? -3000 K -30 billion K -3 K -30 K
3 K
The light that arrives at Earth from the Coma cluster of galaxies has traveled for approximately how long? -92 million years -300 million years -30 million years -300 billion years
300 million years
Suppose you are in the Space Shuttle in orbit around Earth at a speed of 7 km/s, and at some particular time your direction of travel is straight toward the Sun. The speed of light in a vacuum is 300,000 km/s. What speed will you measure for light from the Sun? -300,014 km/s because your speed is added to that of the light, and relativistic contraction has shortened the meterstick used in the measurement of the speed of the light -300,007 km/s because your speed is added to that of the light - 300,000 km/s -300,007 km/s because relativistic contraction has shortened the meterstick with which you measure the distance traveled by the light in order to measure its speed.
300,000 km/s
What appear to be the characteristics of the object at the center of the Milky Way Galaxy? -5 billion solar masses in a volume smaller then Jupiter's orbit -20 solar masses in a volume the size of the Sun -several trillion solar masses in a volume 2 ly in diameter -4 million solar masses in a volume the size of the solar system
4 million solar masses in a volume the size of the solar system
A planetary nebula is a -gas shell, the atmosphere of a red giant star, slowly expanding away from the core of the star. -contracting spherical cloud of gas surrounding a newly formed star in which planets are forming. -nebula caused by the supernova explosion of a massive star. -disk-shaped nebula of dust and gas rotating around a relatively young star in which planets will eventually form.
A gas shell
How does the universe behave, according to the steady-state theory? -The universe is static, neither expanding nor contracting, thus maintaining a "steady state" in which no change takes place. -As the universe expands, new matter is created from which new galaxies form, thus maintaining a "steady state." -The universe is static, not expanding or contracting, but new matter is being created so that as old galaxies die, new galaxies form to take their place. -New matter is being continuously created, which adds to the absorption of light in the universe and makes distant galaxies seem farther and farther away.
As the universe expands, new matter is created from which new galaxies form, thus maintaining a "steady state."
How does a gravitational field affect the passage of time? -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. -Gravity has no effect on the passage of time. -Gravity makes time stop. -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.
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.
Why is Cygnus X-1 thought to be a black hole? -No light has ever been observed to come from Cygnus X-1. - Cygnus X-1 is smaller than Earth, but its mass is too large to be a neutron star or white dwarf. -Cygnus X-1 emits X rays that flicker on time scales of 1/100 second, a unique characteristic of a black hole. -Cygnus X-1 has pulled matter from its companion star into an accretion disk around itself.
Cygnus X-1 is smaller than Earth, but its mass is too large to be a neutron star or white dwarf.
Why are we on Earth able to see only a relatively small part of the Milky Way Galaxy? - Distant stars are obscured by dust in interstellar space. -There are so many stars in the Milky Way that the more distant ones are hidden behind the nearer ones. -Distant stars are obscured by gas in interstellar space. -Expansion of the universe has carried the more distant stars out of our view.
Distant stars are obscured by dust in interstellar space.
We detect the slight anisotropy in the cosmic microwave background by making redshift measurements wavelengths coming from the direction of Aquarius are slightly longer and those from the direction of Leo are slightly shorter. This redshift is a -gravitational redshift. -Doppler shift, gravitational redshift, or cosmological redshift since all three are one and the same thing. -Doppler shift. -cosmological redshift.
Doppler shift
The event that settled the Curtis-Shapley debate was -Edwin Hubble measuring the distance to the Andromeda Galaxy. -Edwin Hubble showing that the universe was expanding. -Arno Penzias and Robert Wilson detecting the cosmic microwave background radiation. -Albert Einstein showing that gravity can bend the path of light.
Edwin Hubble measuring the distance to the Andromeda Galaxy.
The forces of gravity and electromagnetism are long-range forces, extending in principle from their source (mass and electric charge, respectively) to infinity. Why is it that, in the universe, only gravity extends to infinity, whereas electromagnetic forces are much more limited in extent? -Gravity and electromagnetism are one and the same force, with electromagnetic effects extending over limited spatial ranges and transforming into gravitational forces at large distances from matter. -All atoms are electrically neutral, so in reality the electromagnetic force never reaches beyond the size of an atomic nucleus. -Electromagnetic forces from charged particles will move other charged particles around to produce a uniform charge distribution and therefore zero electromagnetic forces, whereas gravity concentrates mass and enhances the overall gravity force. -Electromagnetic forces from positive charges are canceled by negative charges, whereas there are no negative "masses" to cancel the gravitational force.
Electromagnetic forces from positive charges are canceled by negative charges, whereas there are no negative "masses" to cancel the gravitational force.
As we look at more distant regions of space, we see the regions as they existed at earlier times, but our farthest views are blocked by a "wall" beyond which the universe is opaque. What event occurred at the time marked by this wall? -Electrons and protons combined to form neutral hydrogen atoms. -Quarks combined to form neutrons and protons. -Gravity froze out as a separate force. -Protons combined with neutrons to form helium nuclei.
Electrons and protons combined to form neutral hydrogen atoms.
The last supernova in our galaxy which was visible to the naked eye was observed when? -They are quite common, so we undoubtedly saw one within the last year. -There are reports of a supernova eruption in 1066. -We have never seen a naked-eye supernova. -Galileo wrote of a naked-eye supernova in 1604. This was the most recent one.
Galileo wrote of a naked-eye supernova in 1604. This was the most recent one
What is the distribution of giant molecular clouds in the Milky Way Galaxy and other similar galaxies? -Giant molecular clouds are distributed uniformly throughout the disk. -Giant molecular clouds are distributed throughout the halo, with greater density toward the center. -Giant molecular clouds occur primarily in the spiral arms. -Giant molecular clouds are concentrated close to the galactic center.
Giant molecular clouds occur primarily in the spiral arms.
Our view of the universe is limited because of what fundamental fact? -The matter expanding into space from the Big Bang extends only so far since matter can travel only at or below the speed of light. -The cosmological redshift has moved the light from very distant objects out of our detectable range, making these objects invisible to us. -Intergalactic space contains absorbing material that blocks our view of more distant objects. -Light from objects farther away than a certain distance, defined by the travel time of light in the lifetime of the universe, has not yet reached us.
Light from objects farther away than a certain distance, defined by the travel time of light in the lifetime of the universe, has not yet reached us
What is it that makes the study of the structure of the Milky Way Galaxy more difficult than that of much more distant spiral galaxies? -Most of the Milky Way is hidden behind dense gas and dust clouds in the galactic plane. -The Sun is within the Galaxy, and its motion confuses the interpretation of the motion of other parts of the Galaxy. -The galactic center is visible only from the southern hemisphere, where, until recently, no major telescopes were available for the study of galactic structure. -The Milky Way appears to be unique, with a structure quite unlike any other galaxy.
Most of the Milky Way is hidden behind dense gas and dust clouds in the galactic plane.
As you are investigating a black hole from a safe distance, a rivet pops out of the tailfin on your spaceship and falls toward the black hole. Will you ever see the rivet enter the event horizon? - No. It will be compressed to zero size and disappear from sight before it reaches the event horizon. -Yes. You will see it fall faster and faster until it disappears as it falls through the event horizon. -No. It will appear to stop and hover forever before entering the event horizon. -Yes. However, it will be so blueshifted that you would need X-ray eyes to see it.
No. It will appear to stop and hover forever before entering the event horizon
Suppose you are in a jet airliner traveling at a constant speed of 400 km/h in a constant direction. All windows are blocked, so you cannot see outside, and there are no vibrations from the engines. What experiment can you do to determine that you are in fact moving? -Measure the speed of a sound wave traveling up the aisle (toward the nose of the aircraft) and another traveling down toward the tail, and calculate the difference between the two results. -None—all experiments will give the same results that you would get when at rest on the ground. -Suspend a ball by a thread from the ceiling and measure the angle the thread makes with the vertical. -Drop a small rock and measure the distance it moves backward down the aisle as it falls.
None—all experiments will give the same results that you would get when at rest on the ground.
Which of the following statements correctly describes cosmic censorship? -Nothing can leave a local region of space that contains a singularity. -Black holes cannot have magnetic fields. -All properties of the matter inside a black hole are hidden by the event horizon, except for the total mass of the matter. -The amount of mass in a black hole can never be measured.
Nothing can leave a local region of space that contains a singularity.
What is the role of black holes in galaxy formation? -Black holes form simultaneously with galaxies as matter falls in from a large cloud in response to gravity. -Black holes appear to play a role only in determining whether a spiral galaxy will be normal or barred, those with black holes becoming barred. -The black holes at the centers of galaxies form only long after the original formation of the galaxy, so they appear to have no role in its formation. -Pre-existing black holes act as focal points for galaxy formation, attracting matter and becoming the nucleus of the galaxy.
Pre-existing black holes act as focal points for galaxy formation, attracting matter and becoming the nucleus of the galaxy.
In which direction do galaxies evolve on the Hubble "tuning fork" classification scheme and what is the evolutionary significance of this diagram, shown in Figure 16-14 of Comins and Kaufmann, Discovering the Universe, 9th ed.? -Elliptical galaxies slowly condense and spin up to form spiral galaxies, the increasing stellar collisions forming the interstellar material in the spiral arms. -Stars slowly die and the spiral arms slowly spin up and tighten to transform spiral galaxies into elliptical galaxies. -Present evidence suggests that galaxies do not evolve from one kind to another. - The "young" irregular and lenticular galaxies in the center of the "tuning fork" evolve to either elliptical galaxies if the material is metal-poor or spiral galaxies if the material is metal-rich.
Present evidence suggests that galaxies do not evolve from one kind to another.
Which of the following amazing observational facts about quasars and their behavior is perhaps the most extraordinary? -The recession velocities or quasars can be up to 9/10 of the speed of light. -Quasars have incredible power as radio emitters, such that simple receivers can detect them from vast distances across the universe. -The distance of quasars from the Sun is up to 18 billion ly. -Quasars have an energy output equivalent to more than 100 ordinary galaxies from a volume as small as our planetary system.
Quasars have an energy output equivalent to more than 100 ordinary galaxies from a volume as small as our planetary system.
What is the Hubble classification of the Milky Way Galaxy? -Because of the difficulty of examining the structure of the Milky Way from inside, the Galaxy has not been classified. -Sab -SBab -E5
SBab
What is the Hubble classification for a spiral galaxy with a large nuclear region and very tightly wound arms? - SBc - Sa - Sc - E0
Sa
In which constellation in the Earth's sky is the center of the Milky Way Galaxy located? -Hercules -Sagittarius -Lyra -Ursa Major
Sagittarius
An astronomer studying a distant cluster of galaxies finds that several of the galaxies are spiral-shaped, with a small nuclear region and loosely wound arms. How should the astronomer classify these galaxies? -SBb -Sb -Sa -Sc
Sc
What is the Hubble classification for a spiral galaxy with a small nuclear region and very loosely wound arms? -E0 -Sc -SBa -Sa
Sc
What name is given to a nonrotating black hole? -Kerr black hole -Schwarzschild black hole -wormhole -Hawking singularity
Schwarzchild black hole
A spiral galaxy with a bright, starlike nucleus showing strong emission lines is called a -Seyfert galaxy. -quasar. -BL Lacertae object. -gravitational lens.
Seyfert galaxy
According to general relativity, why does Earth orbit the Sun? -Earth and the Sun are continually exchanging photons of light in a way that holds Earth in orbit. -Matter contains quarks, and Earth and the Sun attract each other with the "color force" between their quarks. -The Sun exerts a gravitational force on Earth across empty space. -Space around the Sun is curved, and Earth follows a geodesic in this curved space.
Space around the Sun is curved, and Earth follows a geodesic in this curved space.
What recent evidence seems to indicate that several nearby galaxies may contain supermassive black holes at their centers? -Extreme redshift of light from stars near the centers of these galaxies is caused by gravitational redshift from a very massive object. -Spectroscopic observations of stars near the centers of these galaxies show extremely fast orbital velocities, indicating the presence of a large mass to keep stars in orbit. -The rotation curve of these galaxies shows no decrease in orbital velocity of stars as the radius of orbit increases out to the observable limit of the galaxy, indicating an unusual source of gravity. -These galaxies are rushing rapidly toward each other (and in at least one case, toward the Milky Way!) because of the gravitational attraction among them.
Spectroscopic observations of stars near the centers of these galaxies show extremely fast orbital velocities, indicating the presence of a large mass to keep stars in orbit.
Why do the spiral arms show up so clearly in spiral galaxies? -Stars are spread uniformly over the galaxy, but the dust forms a spiral pattern, absorbing starlight; the spiral arms are the dust-free regions between the dust lanes. -The number of stars in the arms is several times larger than in the regions between, so these arms are reasonably distinct. -Stars occur only in the spiral arms (and the nuclear bulge), with essentially none between the arms, so the arms show up very distinctly. -Stars are spread almost uniformly over the galaxy (outside the nuclear bulge), but the brightest stars occur only in the spiral arms, where their brightness and the fact that they illuminate gas clouds make the arms stand out.
Stars are spread almost uniformly over the galaxy (outside the nuclear bulge), but the brightest stars occur only in the spiral arms, where their brightness and the fact that they illuminate gas clouds make the arms stand out.
Why is the Coma cluster of galaxies a favorite among astronomers? -The Coma cluster is the rich, regular cluster nearest the Earth. -The Coma cluster is the cluster in which the Milky Way Galaxy is situated. -The Coma cluster is the rich, irregular cluster nearest the Earth. -The Coma cluster contains two quasars.
The Coma cluster is the rich, regular cluster nearest the Earth
According to Newton's law of gravity, why does Earth orbit the Sun? -The Sun exerts a gravitational force on Earth across empty space. -Earth and the Sun are continually exchanging photons of light in a way that holds Earth in orbit. -Matter contains quarks, and Earth and the Sun attract each other with the "color force" between their quarks. -Space around the Sun is curved
The Sun exerts a gravitational force on Earth across empty space.
Which of the following statements correctly describes our current state of knowledge about the future expansion of the universe? -The amount of matter (both visible and dark) is only 1/3 of the amount needed to halt expansion, so the expansion will continue to slow down but will never stop. -The amount of matter (both visible and dark) is only 1/3 of the amount needed to halt expansion, and there is mounting evidence of a previously unknown form of energy that acts to accelerate the expansion. -The amount of matter (both visible and dark) is three times the amount needed to halt expansion, so the expansion will eventually stop and the universe will begin to collapse. -The amount of matter (both visible and dark) is exactly the right amount needed to halt expansion after an infinite amount of time has gone by.
The amount of matter (both visible and dark) is only 1/3 of the amount needed to halt expansion, and there is mounting evidence of a previously unknown form of energy that acts to accelerate the expansion.
How do most spiral galaxies rotate? -We do not know; spiral galaxies rotate far too slowly for us to have seen any motion in the time since galaxies were discovered. -Spiral galaxies do not rotate; if they did, the spiral pattern would soon disappear. -The arms trail as the galaxy rotates (the arms point backward). -The arms lead as the galaxy rotates (the arms point forward).
The arms trail as the galaxy rotates (the arms point backward).
A space freighter accidentally drops a steel beam while passing a black hole, and the beam starts falling toward the black hole with the long direction of the beam pointing toward the black hole. What happens to the beam as it approaches the event horizon? -The beam expands in all dimensions to the size of the black hole event horizon when it reaches this distance from the singularity. -The beam is compressed in length and stretched in width. -The beam is compressed in both length and width. -The beam is stretched in length and compressed in width-.
The beam is stretched in length and compressed in width
How does the cosmological constant differ from quintessence? -The cosmological constant provides an accelerating force in the universal expansion, whereas quintessence provides a decelerating term; it is the balance between the cosmological constant and quintessence that determines whether the expansion accelerates or decelerates. -There is essentially no difference; basically, quintessence is the modern name for the cosmological constant. -The cosmological constant is a specific physical effect that can be described mathematically, whereas quintessence is the total of all indefinable properties that make the universe what it is at any given time. -The cosmological constant provides a constant accelerating force in the universal expansion, whereas quintessence can change as the expansion proceeds.
The cosmological constant provides a constant accelerating force in the universal expansion, whereas quintessence can change as the expansion proceeds.
What is the distribution of stars in the spiral arms of a typical spiral galaxy? -Far fewer but brighter stars exist in the arms, while many more fainter stars exist between the arms. -All the stars of a spiral galaxy are in the arms; there are none at all between the arms. -The density of stars in the arms is far higher than the density of stars between the arms. -The density of stars is relatively uniform in the disk of the galaxy but is slightly higher within the arms than between them.
The density of stars is relatively uniform in the disk of the galaxy but is slightly higher within the arms than between them
What appears to be the relationship between the distribution of dark matter and the distribution of luminous matter? -The distribution of dark matter seems to be just the reverse of the distribution of luminous matter -Dark-matter galaxy clusters occur in the voids of luminous matter; luminous galaxy clusters occur in the voids of dark matter. -There seems to be a separate distribution of dark matter-dark-matter galaxy clusters, voids in the dark matter, and so on. But these formations all occur in regions of space far from luminous matter. -The distribution of dark matter seems to coincide with the distribution of luminous matter. -There seems to be no correlation at all.
The distribution of dark matter seems to coincide with the distribution of luminous matter.
When a solar mass star is ejecting a planetary nebula, the temperature of its exposed core can reach 100,000 K. How does this temperature compare with the core temperature when the star is on the main sequence? -The exposed core is cooler because it is at the end of its fuel supply. -The exposed core is hotter because it was heated by carbon-oxygen fusion rather than hydrogen fusion. -The exposed core is cooler simply because it is exposed to the cold regions of space. -The exposed core is hotter because it was heated by helium fusion rather than hydrogen fusion.
The exposed core is hotter because it was heated by helium fusion rather than hydrogen fusion
What would happen to the gravitational force on Earth if the Sun were to be replaced by a 1-solar-mass black hole? -The gravitational force on Earth would remain as it is now. -The gravitational force on Earth would become extremely high, sufficient to pull Earth into the black hole. -The gravitational force on Earth would double in strength. -The gravitational force on Earth would be much less because the gravitational field of a black hole exists only very close to it.
The gravitational force on Earth would remain as it is now
Why would we expect the rate of expansion of the universe to be slowing down? -All expansions after explosions naturally slow down with time. -Galaxies feel a kind of friction as they move through space, which slows them down. -The greater the distance between two objects (such as galaxies or superclusters), the harder it is to push them farther apart. -The gravitational pull of all objects in the universe on each other would lead to slowdown.
The gravitational pull of all objects in the universe on each other would lead to slowdown.
A laborer repairing the clock tower on a space station orbiting a black hole accidentally drops the clock in such a way that it accelerates toward the black hole. What does the worker see while watching the clock? -The hands of the clock keep normal time since time is absolute and the same everywhere. -As the clock nears the event horizon, the hands begin to move randomly as time becomes jumbled near the black hole. -The hands of the clock move faster and faster until the clock plunges through the event horizon. -The hands of the clock move slower and slower until they and the clock itself stop at the event horizon.
The hands of the clock move slower and slower until they and the clock itself stop at the event horizon
If the central engine of a double-lobed radio source is a black hole swallowing matter from an accretion disk, where do the jets of matter come from that we see traveling outward from the galaxy? -The jets are accelerated in the ergoregion of the rotating black hole and ejected outward in the black hole's equatorial plane. -The jets arise in the weak galactic magnetic field, not in the region near the black hole. -The jets are composed of material that has been accelerated from two hemispheres toward the black hole with such speed that it escapes again on two opposite sides of the black hole. -The jets are squirted out by high pressure in the accretion disk before the matter reaches the black hole.
The jets are squirted out by high pressure in the accretion disk before the matter reaches the black hole.
Suppose it were possible to lower a yellow sodium lamp toward the event horizon of a black hole. What would you see while watching from a safe distance? -The brightness and color would each remain unchanged. -The light would remain yellow, but there would be fewer and fewer photons being emitted from it. -The light from the lamp would change to green and then blue. -The light from the lamp would change to orange and then red.
The light from the lamp would change to orange and then red
What do we expect to be the relationship between the number of active galaxies we detect and the number of active galaxies that actually exist? -We cannot detect active galaxies unless the jets are pointed more or less toward Earth. The jets point toward Earth in only a few cases, so we expect the actual number to be greater than the observed number. -Active galaxies are created in galaxy collisions. But galaxy collisions occurred only in the early universe and are no longer occurring. The active galaxies all died off while their light was traveling to Earth. -The nuclei of many active galaxies are hidden by dust in the accretion disk. Thus we expect the actual number to be much greater than the observed number. -The energy output from active galaxies is so large that it is easy to detect them. Thus we believe we have detected all that exist.
The nuclei of many active galaxies are hidden by dust in the accretion disk. Thus we expect the actual number to be much greater than the observed number.
Which of the following is a characteristic of a Seyfert galaxy? -The spectrum of a Seyfert galaxy shows particularly narrow absorption lines. -The nucleus of a Seyfert galaxy is unusually faint compared with the spiral arms. -The nucleus of a Seyfert galaxy is unusually bright compared with the spiral arms. -A Seyfert galaxy has no spiral arms.
The nucleus of a Seyfert galaxy is unusually bright compared with the spiral arms.
If you see an object moving past you at 90% of the speed of light, what will its length appear to be? -The object will look shorter than if it were at rest. -The object will look shorter than if it were at rest while it is coming toward you and longer after it has passed you. -The length of the object will appear to be unchanged from when it is at rest since it is a solid object. -The object will look longer than if it were at rest.
The object will look shorter than if it were at rest.
How does the observed amount of visible matter in the universe compare with the amount required to just close the universe? -The observed amount of visible matter is about 1/3 of the amount needed. -The observed amount of visible matter equals the amount needed, to within observational uncertainty. -The observed amount of visible matter is about 1/200 of the amount needed. -The observed amount of visible matter is about twice the amount needed
The observed amount of visible matter is about 1/200 of the amount needed.
In observations of a double quasar image produced by gravitational lensing, fluctuations on the intensity of one image appear to be delayed compared with equivalent variations on the other image. Explain. -The gravitational field of the lensing object slows down the light on one beam compared with the other. -One beam has had to pass through material with a greater refractive index than for the other beam within the lensing galaxy. -The optical path through the gravitational lens producing one image is longer than that for the other image. -Rotation of the lensing galaxy has delayed the beam of light on one side compared with the other because of the Doppler effect.
The optical path through the gravitational lens producing one image is longer than that for the other image
What is the origin of the rings of gas that surround Supernova 1987A? -The rings were formed when the shock wave lifted the outer layers of the star. -These rings were pushed out by the core bounce. -These were caused by the gamma rays, which also caused photodisintegration. -The rings were formed by stellar winds before the supernova erupted.
The rings were formed by stellar winds before the supernova erupted
Why do astronomers believe the binary companions of the white dwarf stars which produce Type Ia supernovae are most probably main-sequence stars? -A smaller star would not be able to fill its Roche lobes and a larger star would swallow the white dwarf before it could produce a supernova. -Only main-sequence stars have lifetimes which would allow them to fill their -Roche lobes at the same time their companion (formed at the same time) is a white dwarf. -We detect white dwarf binaries mostly by the astrometric method of looking for a wobble in the primary star's motion. Only a main-sequence star would be massive enough for this wobble to be detected. -The supernova explosion will cause the atmosphere of the binary companion to glow. We do not detect enough afterglow to suggest a giant or supergiant as a companion.
The supernova explosion will cause the binary companion to glow...
Which of the following statements correctly describes the universe for the entire first 380,000 years of its life? -The universe was opaque. -The universe was a filled with a sea of nuclear particles undergoing violent reactions. -All the fundamental forces of nature were unified into one force. -The universe was filled with free quarks (not confined inside neutrons or protons).
The universe was opaque.
Photodisintegration, the fissioning of iron nuclei into helium nuclei by high-energy gamma radiation, occurs only at the very end of the life of a massive star. Why can photodisintegration not occur earlier? Choose the answer that is not correct. -The fissioning of an iron nucleus requires energy, and the energy-rich environment that allows fissioning to happen does not exist before this stage. -Iron nuclei do not exist in anything but trace amounts before this stage. -Under the conditions of the previous stages of evolution, iron (26Fe) disappears as quickly as it is formed by combining with helium (4He) to produce zinc (30Zn). -Gamma radiation of sufficient energy is not produced before this stage.
Under the conditions of the previous stages of evolution, iron (26Fe) disappears as quickly as it is formed by combining with helium (4He) to produce zinc (30Zn).
Why does the observable universe have an "edge"? -We cannot see any farther out into space than the distance that light has traveled over the lifetime of the universe -There are so many galaxies in the universe that every line of sight eventually hits a galaxy, stopping us from seeing any farther -Absorbing matter prevents us from seeing beyond a certain distance -The density of neutrinos at the "edge" becomes so large that photons cannot penetrate this barrier, and this prevents us from seeing beyond this point
We cannot see any farther out into space than the distance that light has traveled over the lifetime of the universe
If we could have turned a receiver toward the heavens in hopes of observing the cosmic microwave radiation 4.5 billion years ago, at the time the solar nebula was forming, what would we have found? -We would have seen the same blackbody curve we see now, with a peak intensity at a wavelength of about 1 mm. -We would have seen a blackbody curve of the same shape we see now but with a peak intensity at a wavelength shorter than 1 mm. -We would have seen nothing since the CMB had not yet been created. -We would have seen a blackbody curve of the same shape we see now but with a peak intensity at a wavelength longer than 1 mm.
We would have seen a blackbody curve of the same shape we see now but with a peak intensity at a wavelength shorter than 1 mm.
Why do we believe a magnetar can have a much stronger magnetic field than that of an ordinary neutron star? -Magnetars were formed from supergiant stars many times larger than the stars that produced ordinary neutron stars. -Magnetars are superconducting throughout. -Magnetars have a higher proportion of protons and thus have stronger electric currents. -When first formed as neutron stars, magnetars were spinning rapidly enough that the magnetic fields produced by convection became joined.
When first formed as neutron stars, magnetars were spinning rapidly enough that the magnetic fields produced by convection became joined
What makes gravity the main force determining the large scale structure of the universe? -The gravitational force, while short-ranged, is the only force that affects all particles, photons, quarks, changed particles, uncharged particles. -Gravity is the only force that has an infinite range. -While the electromagnetic force of a charged particle has an infinite range, it is usually screened (and limited) by the existence of charges of the opposite sign. Ordinary matter has only one sign and therefore does not screen other gravitational forces. - Gravity is the strongest of the four fundamental forces
While the electromagnetic force of a charged particle has an infinite range, it is usually screened (and limited) by the existence of charges of the opposite sign. Ordinary matter has only one sign and therefore does not screen other gravitational forces.
Are crystalline stars or crystalline remnants of stars possible; why or why not? -Yes. They are the likely outcome of the creation of iron in the core of a massive star. -No. The forces needed to crystallize a star would actually cause the star to collapse gravitationally into a black hole. -No. Stars and stellar remnants are too hot to crystallize. -Yes. They are the likely outcome of the cooling of a white dwarf.
Yes. They are likely the outcome of the cooling of a white dwarf.
One of the consequences of the collision of two galaxies appears to be -the disappearance of one of them into the central black hole of the other. -almost nothing since stars are widely separated in each galaxy and the probability of star-star collisions is very small. -a very large explosion, similar to but much larger than a supernova, often known as a superdupernova. -a burst of vigorous star birth.
a burst of vigorous star birth
Quasars have now been detected in which the highest redshifts, if translated to "recession velocities," indicate motion away from the Milky Way Galaxy of -speeds greater than the speed of light, indicating that the interpretation of redshifts in terms of velocity is faulty. -a large fraction of the speed of light. -about 1/10 of the speed of light. -speeds as large as 3 × 10^3 km/s, or 1% of the speed of light.
a large fraction of the speed of light.
The explosion of a supernova appears to leave behind -a rapidly expanding shell of gas and a compact white dwarf star at its center. -nothing; the explosion changes all the matter completely into energy, which then radiates into space at the speed of light. -a rapidly expanding shell of gas and a central neutron star. -a rapidly rotating shell of gas, dust, and radiation, but no central object.
a rapidly expanding shell of gas and a central neutron star
The cosmic microwave background is found to be extremely uniform throughout space, with only very small fluctuations in intensity. The event that produced this remarkable smoothness in the early universe was -the occurrence of the Big Bang everywhere in space at the same time. -an exemplar of Heisenberg's uncertainty principle that prevented the concentration of radiant energy in localized volumes of space. -a sudden but brief period of rapid expansion (cosmic inflation) of the universe during the general expansion of the early universe. -the start of the production of matter in the universe, which smoothed out the irregularities in space.
a sudden but brief period of rapid expansion (cosmic inflation) of the universe during the general expansion of the early universe.
When we look into the plane of the Milky Way Galaxy, how far can we see? - infinitely far -about 10,000 ly -less than 1000 ly -about 100,000 ly
about 10,000 ly
How much mass are planetary nebulae estimated to return to the interstellar medium each year over the Galaxy as a whole? -about 5 × 10^8 solar masses -about 50,000 solar masses -about 500 solar masses -about 5 solar masses
about 5 solar masses
What fraction of the mass of the Milky Way Galaxy appears to be in the form of "dark matter," which we cannot see but can detect through its gravitational influence? - about 50% -about 10% -about 90% -0%—who ever heard of matter that can't be seen?
about 90%
The energy generation mechanism for active galaxies is believed to be -cosmic radioactive decay. -black holes colliding. -large numbers of supernovae erupting simultaneously. -accretion disks around supermassive black holes.
accretion disks around supermassive black holes
The weak force -attracts the electrons to the nucleus, holding the atom together. -acts during certain kinds of radioactive decay. -holds the quarks together inside a proton or neutron. -acted only during the Big Bang and has no known role in the universe at the present time.
acts during certain kinds of radioactive decay.
Which parameter of the present universe is considered to be critical in determining the ultimate fate of the universe? -amount of matter and energy in the universe -number of photons of radiation in the universe -number of neutrinos in the universe -amount of mass in black holes in the universe
amount of matter and energy in the universe
The future of the overall universe, in terms of its ultimate evolution and whether it will expand forever or eventually contract again, is determined by which of its parameters? -amount of matter and energy within it -present volume of the universe -temperature of the gas within it -intensity of cosmic microwave background radiation
amount of matter and energy within it
The first pulsar was discovered by -Galileo Galilei in 1610. -Albert Einstein in 1905. -an English graduate student, Jocelyn Bell, in 1967. -the Astronomer Royal in Newton's time, Sir Edmund Halley, in 1606.
an English graduate student, Jocelyn Bell, in 1967.
Astronomy with a radio telescope was initiated by -Maroni in Europe. -the British Broadcasting Corporation in England. -the National Radio Astronomical Observatories of the United States, with the support of the National Science Foundation and the American Astronomical Society. -an amateur astronomer, Grote Reber, after Jansky had detected radio energy from the galaxy.
an amateur astronomer, Grote Reber, after Jansky had detected radio energy from the galaxy.
During which phase of a low-mass star's life does helium shell fusion occur? -asymptotic giant branch -main sequence -horizontal branch -first red-giant phase
asymptotic giant branch
The basic idea of Einstein's theory of General Relativity is that mass causes space to ___________. -bend. -evaporate. -expand. -rotate.
bend.
What is a primordial black hole? -black hole created during the formation of the solar system -black hole at the center of a galaxy -black hole not in orbit around a normal star -black hole created during the formation of the universe
black hole created during the formation of the universe
The specific characteristics that identify most quasars are -bright, starlike appearance and very high spectral blueshift, indicating that they are approaching the Sun very fast, and rapid intensity fluctuations, indicating small intrinsic size. -bright, starlike appearance with very high redshifts and hence very large distances, indicating very energetic sources. -that they look like elliptical galaxies but with high spectral redshifts. -spiral galaxy appearance and very high spectral blueshift, indicating that they are coming toward the Sun at high speed.
bright, starlike appearance with very high redshifts and hence very large distances, indicating very energetic sources.
How can astronomers determine the size of an emission region in a very distant and unresolvable source? - by using radio interferometry since this technique can resolve far greater detail than optical imaging -by measuring the redshift of its spectrum since the redshift will depend on the source size -by measuring the object's mass and using a reasonable value for the average density for matter to calculate its volume and hence its diameter -by measuring brightness variability since an object cannot vary more rapidly than the time taken for light to cross the source
by measuring brightness variability since an object cannot vary more rapidly than the time taken for light to cross the source
How was most of the helium in the universe created? -by nuclear reactions in the cores of stars and then thrown out into space by supernovae -by the collision of cosmic rays with hydrogen nuclei in interstellar gas clouds -by nuclear reactions during the first 3 minutes following the Big Bang -by high-energy processes during the collapse of pregalactic clouds during the formation of galaxies
by nuclear reactions during the first 3 minutes following the Big Bang
Which nuclear fusion cycle is the next one to begin after helium fusion ends in a massive star? -iron fusion -oxygen fusion -silicon fusion -carbon fusion
carbon fusion
When we measure the narrow line emissions of hydrogen at 21-cm radio wavelengths along a particular line of sight through the disk of the Milky Way Galaxy, we can tell the distances to different hydrogen clouds because -clouds at different distances have different Doppler shifts because of the rotation of the Galaxy -clouds that are farther away have smaller angular sizes. -absorption of extragalactic radiation at this wavelength is greater the farther away the absorber is from the Sun. -the emission is weaker from clouds that are farther away.
clouds at different distances have different Doppler shifts because of the rotation of the Galaxy
What is a rich cluster of galaxies? -cluster with a high metal content -cluster containing thousands of galaxies -cluster (like our Local Group) that contains at least two large galaxies -cluster with more spiral galaxies than ellipticals
cluster containing thousands of galaxies
What mechanism is believed to produce grand-design spiral galaxies? -satellite galaxies plunging through the disk of the nuclear spiral galaxy -density waves in the interstellar medium -self-propagating star formation, where star formation occurs in bursts -shock waves from explosive star formation in the nuclear bulge
density waves in the interstellar medium
When a high-energy gamma-ray photon collides with a nucleus, the gamma-ray photon -disappears, creating a particle-antiparticle pair. -disappears completely, leaving nothing behind. -produces a huge number of low-energy photons. -disappears, creating two negative electrons.
disappears, creating a particle-antiparticle pair.
What important role do Cepheid variables stars have in astronomy? -determination of stellar luminosities -determination of speeds of stars in galactic arms from the Doppler shift of their spectra -keeping of accurate time -distance measurements to distant galaxies
distance measurements to distant galaxies
If you were to pass inward through the event horizon of a black hole, you could -escape again provided that the black hole is spinning. -move outward within the black hole with a powerful rocket, thereby avoiding the singularity until your fuel ran out, but you could never escape back out through the event horizon. -do nothing to prevent yourself from falling directly into the singularity at the center. -avoid the singularity by going into orbit around it, but you could never move outward again from any particular orbit.
do nothing to prevent yourself from falling directly into the singularity at the center.
Which component of the Milky Way Galaxy accounts for interstellar extinction, the dimming of light from distant objects? -so-called hidden or missing matter since its absorbing properties render it invisible in the Galaxy -dust -cool hydrogen gas -molecules such as hydrogen and carbon monoxide, which are strong absorbers, in molecular clouds
dust
Massive black holes have been discovered in the cores of what kinds of galaxies? - spirals - giant ellipticals - giant ellipticals and spirals - dwarf ellipticals, giant ellipticals, and spirals
dwarf ellipticals, giant ellipticals, and spirals
Which of the following actions will a high-mass star (say, 25 times the mass of the Sun) not do at or near the end of its life? -eject its outer layers and become a white dwarf -emit copious amounts of neutrinos -eject its outer layers and become a neutron star -convert silicon into iron in its core
eject its layers and become a white dwarf
The cosmic background radiation is the -electromagnetic remnants of the explosion in which the universe was born. -radio noise from hot gas in rich clusters of galaxies. -faint glow along the elliptic, caused by sunlight scattering from dust particles. -result of the radioactive decay of heavier, unstable elements produced in supernova explosions.
electromagnetic remnants of the explosion in which the universe was born
The cosmic background radiation is the -electromagnetic remnants of the explosion in which the universe was born. -radio noise from hot gas in rich clusters of galaxies. -faint glow along the elliptic, caused by sunlight scattering from dust particles. -result of the radioactive decay of heavier, unstable elements produced in supernova explosions.
electromagnetic remnants of the explosion in which the universe was born.
In which category of galaxy do we find the largest galaxies in the universe? -irregular galaxies -lenticular galaxies -large spiral galaxies like the Milky Way -elliptical galaxies
elliptical galaxies
The escape velocity at the event horizon around a black hole is -equal to the speed of light. -just under the speed of light. -infinite. -much less than the speed of light.
equal to the speed of light
A planetary nebula is a(n) -expanding gas shell surrounding a hot, burned-out stellar core. -contracting spherical cloud of gas surrounding a newly formed star in which planets are forming. -nebula caused by the supernova explosion of a massive star. -disk-shaped nebula of dust and gas around a relatively young star, from which planets will eventually form.
expanding gas shell surrounding a hot, burned-out stellar core.
What kind of curvature (geometry of space) does the universe have if the universe is just on the boundary between being open and being closed? -spherical -parabolic -hyperbolic -flat
flat
How many fundamental forces are known in science at the present time under normal conditions? -six -five -three -four
four
The Milky Way Galaxy appears to have a spiral structure with - one "arm" wound around the nucleus four times. -four separate major arms. -three loosely wound arms. -two major arms wound twice around the nucleus.
four separate major arms.
The jets of material moving away from a supermassive black hole are generated by high pressures and temperatures at the base of the accretion disk. What causes these high pressures and temperatures? -friction -radioactivity -helium fusion -hydrogen fusion
friction
How has the mass of the black hole candidate Cygnus X-1 been estimated? -from the observed size and estimated density of the object -from the periodic wobble it produces in the spectral lines of a normal companion star around which it orbits -from the periodic wobble in its own characteristic black-hole spectrum -from the gravitational redshift, where the more massive the object, the greater the redshift of its spectral lines
from the periodic wobble it produces in the spectral lines of a normal companion star around which it orbits
What is a barred spiral galaxy? -spiral galaxy with a straight bar instead of a nuclear bulge -galaxy with a bar extending across the entire diameter and the arms starting at various positions along the bar -galaxy with a bar through the nuclear bulge and the spiral arms starting from the ends of the bar -galaxy in which the arms form straight bars instead of curved lines
galaxy with a bar through the nuclear bulge and the spiral arms starting from the ends of the bar
What is a lenticular (or S0) galaxy? -spiral galaxy with fuzzy and poorly formed spiral arms -galaxy with a central bulge and a disk like a spiral galaxy, but with no spiral arms -galaxy with a smooth brightness profile and lacking the central bulge and disk of a spiral galaxy -galaxy with a lot of gas and dust and no particular structure
galaxy with a central bulge and a disk like a spiral galaxy, but with no spiral arms
What is an SBc galaxy? -galaxy with a small nuclear bulge and loosely wound arms starting from the ends of a straight bar through the nuclear bulge -galaxy with a large nuclear bulge and tightly wound arms starting from the ends of a straight bar through the nuclear bulge -galaxy with a moderate nuclear bulge, moderately wound arms, and a bright core -galaxy with a small nuclear bulge and loosely wound arms coming from the center of the nuclear bulge
galaxy with a small nuclear bulge and loosely wound arms starting from the ends of a straight bar through the nuclear bulge
What is an E3 galaxy? -galaxy with a smooth light distribution and a moderately elliptical shape, having a pronounced disk and central bulge -galaxy with an irregular light distribution and a very elongated shape -galaxy with a smooth light distribution and a moderately elongated elliptical shape without a disk or central bulge -galaxy with a smooth light distribution and a very elongated elliptical shape without a disk or central bulge
galaxy with a smooth light distribution and a moderately elongated elliptical shape without a disk or central bulge
What is an elliptical galaxy? -spiral galaxy seen from an angle, giving it an elliptical profile -galaxy with an elliptical halo when observed at radio wavelengths -spiral galaxy with an elliptically shaped nuclear bulge and the spiral arms starting from the ends of the ellipse -galaxy with an elliptical outline and a smooth distribution of brightness but no apparent structure
galaxy with an elliptical outline and a smooth distribution of brightness but no apparent structure
The escape velocity of matter from the center of a black hole is -about half the speed of light. -quite small. -always exactly equal to the speed of light. -greater than the speed of light.
greater than the speed of light.
Seyfert galaxies are a distinct class of galaxies because they -are very close to the Milky Way and appear to be gravitationally bound to it. -have very bright, very hot starlike central cores with variable energy output. -are completely devoid of structure, appearing to be amorphous spheres of gas and dust. -are in the constellation of Seyfert in Earth's southern hemisphere sky.
have very bright, very hot starlike central cores with variable energy output.
Which of the following processes is not involved in the supernova explosion of a massive star? -passage of a shock wave through the star's envelope -helium flash in the star's core -collapse of the star's core -photodisintegration of nuclei by gamma rays
helium flash in the star's core
What kind of curvature (geometry of space) does the universe have if the universe is open? -parabolic -hyperbolic -flat -spherical
hyperbolic
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 asteroid belt -in elliptical galaxies since they are composed of old stars and do not exist in young systems like spiral galaxies -in the Milky Way disk, moving in a circular orbit around the galactic center
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 -only at the galactic center. -everywhere. -in the disk and spiral arms. -in the globular clusters in the galactic halo.
in the disk and spiral arms
Where is the solar system located in the Milky Way Galaxy? - in the galactic halo - The solar system is not in a galaxy but in the intergalactic space between galaxies. -in the galactic nucleus -in the galactic disk
in the galactic disk
What is the range of the gravitational force (the maximum distance over which it acts)? -infinity -10^21 m, or roughly the size of the Milky Way Galaxy -10^13 m, or roughly the size of the solar system -10^26 m, or roughly the distance to the farthest quasars
infinity
Where are bright, young O and B stars most likely to be found in the Milky Way Galaxy? -inside spiral arms -in the outermost regions of the disk, where much of the "dark matter" is located -in globular clusters -between spiral arms, where there is less absorbing material
inside spiral arms
At which of the following locations will Newton's laws of motion be inadequate in describing precisely the motions of objects? - inside an artillery shell as it accelerates inside the gun barrel - in the Space Shuttle, moving around Earth at a speed of about 8 km/sec -at the center of Earth -inside the orbit of Mercury
inside the orbit of mercury
What atomic transition occurs in the atoms of hydrogen gas in the spiral arms of the Milky Way Galaxy to produce the 21-cm radio emission? -change in rotation of the hydrogen molecule about an axis perpendicular to the molecular axis -transition from n 2 level to n 1 level in atomic hydrogen -inversion of the electron spin relative to the proton spin, from parallel to antiparallel -change in the vibrational state of the H atoms in the hydrogen molecule
inversion of the electron spin relative to the proton spin, from parallel to antiparallel
The Magellanic Clouds as seen from the southern hemisphere are examples of what type of objects? -irregular galaxies -spiral galaxies -planetary nebulae -supernova remnants
irregular galaxies
According to the Hubble classification scheme, an E6 galaxy -is rounder looking than an E2 galaxy. -has a shorter central bar in its disk than an E2 galaxy. -has more tightly wound spiral arms than an E2 galaxy. -is more elongated than an E2 galaxy.
is more elongated than an E2 galaxy
The discovery of the peculiar galaxy Cygnus A was a surprise to astronomers because -it was so bright at optical wavelengths that no one expected it to be a galaxy. -it was first discovered at X-ray wavelengths and detected at optical and radio wavelengths only some time later. -it was very faint at visible wavelengths but extremely bright at radio wavelengths. -the redshift of its radio wavelength signal was as high as anything measured up to that time.
it was very faint at visible wavelengths but extremely bright at radio wavelengths.
What is the Great Attractor? -large collection of mass about 50 Mpc from Earth in the direction of the Hydra-Centaurus supercluster toward which the Local Group of galaxies is being drawn -immense black hole thought to be at the center of the universe and a remnant of the cosmic singularity -immense black hole somewhere in the universe from the accretion disk of which the cosmic 3-K background radiation is believed to be emitted -supermassive black hole at the center of the Milky Way Galaxy
large collection of mass about 50 Mpc from Earth in the direction of the Hydra-Centaurus supercluster toward which the Local Group of galaxies is being drawn
In terms of the evolutionary life of a star, at what stage is the Crab Nebula? -beginning- nebula in which stars are forming -late- it is the remnant of a star explosion or supernova -middle-age- main-sequence star, relatively near the Sun -black hole- very late stage of evolution
late, it is the remnant of a star explosion or supernova
Consider a group of stars with masses up to 8 times the mass of the Sun. Stars of which masses will end up as pure helium? -less than 0.4 solar masses -all stars 0.4 to 8 solar masses -0.4 to 2 solar masses only -2 to 8 solar masses only
less than 0.4 solar masses
The Milky Way Galaxy is a(n) -isolated galaxy, not a member of any cluster. -member of a small cluster of galaxies. -member of a large, irregular cluster of thousands of galaxies. -member of a large, regular cluster of thousands of galaxies.
member of a small cluster of galaxies
Interstellar matter obscures our view of the disk of the Milky Way Galaxy -very little at any wavelength. -more or less equally at all wavelengths, from radio waves to light waves. -more at optical wavelengths and less or not at all at infrared and radio wavelengths. -most at radio wavelengths, where hydrogen absorbs radio waves efficiently, and least at optical wavelengths.
more at optical wavelengths and less or not at all at infrared and radio wavelengths.
Suppose you are aboard a spaceship that is passing Earth at 80% of the speed of light. You see a clock on Earth tick off 5 seconds. How much time elapses on your own clock while this is happening? -5 seconds—the same as on the ship's clock -more than 5 seconds if you are approaching Earth and less than 5 seconds if you are moving away from Earth -less than 5 seconds -more than 5 seconds
more than 5 seconds
The highest recession velocities that have recently been detected for quasars are -almost half the speed of light. -more than 90% of the speed of light. -3000 km/s, or about 1% of the speed of light. -about 10% of the speed of light.
more than 90% of the speed of light.
All quasars appear to be - relatively close, very bright objects. - moving away from Earth at very high speeds. - very distant, intrinsically faint objects. - moving toward Earth at very high speeds.
moving away from Earth at very high speeds.
Astronomers initially had difficulty identifying the emission lines in quasar spectra at optical wavelengths because -the emission lines were found to be created from elements that do not exist on Earth. -the emission lines were from ionized atoms that had not been seen before. -no one expected to see the pattern of spectral lines characteristic of UV hydrogen spectra in the visible region. -the emission lines were smeared out by the extremely high speed of the quasars, making them hard to measure.
no one expected to see the pattern of spectral lines characteristic of UV hydrogen spectra in the visible region.
What is it that is actually located at the event horizon of a black hole? - magnetic field of immense strength -sphere of photons -infinitely dense concentration of mass -nothing specific
nothing specific
Harlow Shapley first located the center of the Milky Way Galaxy in 1917 by -measuring the positions of supernova explosions throughout the Galaxy. -measuring redshifts of stars in the galactic plane and disk. -observing the distribution of hydrogen gas, measured by 21-cm radio emission. -observing the distribution of globular clusters in the galactic halo.
observing the distribution of globular clusters in the galactic halo
Variations in the output of quasars within a few hours are an indication that -these objects are actually binary systems in which we see mutual eclipses. -of the relatively small size of the emitting regions. -of obscuring gas and dust clouds moving in front of them from our point of view. -of the rapid rotation of the sources.
of the relatively small size of the emitting regions
Which two parameters of star motion in the Milky Way are represented by its rotation curve? -star position above or below the galactic plane as a function of distance from the galactic center -orbital speed of the stars as a function of their individual masses -orbital speed as a function of star distance from the galactic center -orbital period of the stars as a function of their distance from the galactic center
orbital speed as a function of star distance from the galactic center
Quasars -peaked in number about 2 billion years after the Big Bang.. -increase in number as redshift increases, a relationship that persists to the highest redshifts we can measure. -are more common in nearby clusters of galaxies and less common in distant clusters of galaxies. -are rare in the Local Group, with only one or two examples.
peaked in number about 2 billion years after the Big Bang..
The significant feature of a Cepheid variable is that there is a relationship between two intrinsic parameters, one of which can be easily measured, while knowledge of the other parameter is required. These parameters are - amplitude of brightness variation and luminosity. -period of brightness variation and luminosity. -variation of spectral color and distance to the star. -period of brightness variation and spectral color
period of brightness variation and luminosity.
A singularity is a(n) - place where the escape velocity exactly equals the speed of light. -place of infinite density inside a black hole, where a large mass occupies zero volume. -entry point in the event horizon of a black hole through which material is allowed to pass unhindered. -place just outside the event horizon of a rotating black hole where it is impossible to remain at rest.
place of infinite density inside a black hole, where a large mass occupies zero volume.
Cerenkov radiation that was used to detect neutrinos from supernova SN 1987A was produced by -positive electrons (positrons) traveling faster than the speed of light in water. -electrons and antielectrons (positrons) colliding and annihilating. -neutrons ejected from nuclei by the neutrinos. -nuclear fusion produced in the detector by neutrinos.
positive electrons (positrons) traveling faster than the speed of light in water
An elliptical galaxy typically contains which of the following kinds of stars? -stars of all ages from young, metal-rich stars to old, metal-poor stars -stars of all ages, but all metal-poor -primarily old, metal-poor stars -primarily young, metal-rich stars
primarily old, metal-poor stars
"It is starlike in appearance, showing very high redshift and an energy output of at least 100 galaxies from a small region about 1 ly across." These characteristics describe which of the following astronomical objects? -red supergiant star -supernova explosion in a neighboring galaxy -quasar -center of the Milky Way Galaxy
quasar
The X-ray source Cygnus X-1 is a black hole candidate located in a binary star system. The X-ray source is believed to occupy a volume smaller than Earth. This size is deduced from -the shortness of Cygnus X-1's orbital period. -Cygnus X-1's apparent magnitude and distance. -Cygnus X-1's luminosity and spectral class. -rapid flickering in the X-ray brightness of Cygnus X-1.
rapid flickering in the X-ray brightness of Cygnus X-1
What observational fact convinces astronomers that the source of energy in a typical quasar is physically very small? -starlike appearance of quasars in the Earth's sky -rapid variation in the energy output of the source -extreme distance of all quasars -narrowness of the emission lines in the spectra of quasars
rapid variation in the energy output of the source
A pulsar is a(n) -object at the center of each galaxy, supplying energy from its rapid rotation. -pulsating star, in which size, temperature, and light intensity vary regularly. -binary star in which matter from one star is falling onto the second star. -rapidly rotating neutron star, emitting beams of radio energy and sometimes X ray and visible energy.
rapidly rotating neutron star, emitting beams of radio energy and sometimes X ray and visible energy.
Which type of dwarf is largest? -All are about the same size. -red dwarf -brown dwarf -white dwarf
red dwarf
Quasars in our universe are -relatively common. Over 10,000 have been identified so far. -rare. Only about 10 have been positively identified as such by their properties. -relatively rare. Only about 500 have been detected so far. -extremely common. At least 1 million have been catalogued so far.
relatively common. Over 10,000 have been identified so far.
What is the famous Virgo cluster of galaxies? - nearest cluster beyond the Local Group containing about three dozen galaxies - cluster of unknown type centered on a quasar near the edge of the visible universe -rich, irregular cluster of over 1000 galaxies -rich, regular cluster of thousands of galaxies
rich, irregular cluster of over 1000 galaxies
Suppose you are in a spaceship traveling toward Earth at 95% of the speed of light. Compared with when your ship was at rest on Mars, what length do you measure for your spaceship? -longer -shorter -same -You cannot tell; your life processes have slowed down too much for you to measure the length.
same
In the Hubble classification scheme for spiral galaxies, the tightness of the winding of the spiral arms appears to be related directly to the - overall intrinsic size of the galaxy, or the diameter across the spiral arms. -its individual stars. -size of the central bulge of the galaxy. -age of the galaxy, as determined from the age of its individual stars.
size of the central bulge of the galaxy.
Spiral galaxies are classified in terms of increasing tightness of their spiral arms as types Sa, Sb, and Sc. However, many spiral galaxies are aligned edge-on to Earth and their spiral arms cannot be seen. Which other parameter that is directly related to spiral arm tightness can be easily seen edge-on and can therefore be used to provide this classification? -overall spectral color - overall intrinsic brightness of the galaxy, or its absolute magnitude -size of the nuclear bulge -overall diameter of the galaxy
size of the nuclear bulge
If you stay on Earth while a friend races off in a rocket at a speed close to the speed of light, then according to special relativity you will see a clock on the rocket appear to tick more slowly than the one on your wall. If your friend looks back at your clock, then according to the same theory the friend will see your clock appear to tick - faster or slower than the clock on the rocket, depending on the direction of travel of the rocket compared with Earth. -slower than the clock on the rocket. -faster than the clock on the rocket. -at the same speed as the clock on the rocket.
slower than the clock on the rocket.
What kind of curvature (geometry of space) does the universe have if the universe is closed? -flat -hyperbolic -spherical -parabolic
spherical
What is a galactic halo? -system of satellite galaxies surrounding the Milky Way Galaxy -large disk of stars and molecular clouds extending outward from a nuclear bulge -spherical distribution of stars and globular clusters centered on a nuclear bulge -system of arcs and other gas clouds surrounding a galactic nucleus
spherical distribution of stars and globular clusters centered on a nuclear bulge
Pulsating X-ray sources are believed to be -the same as regular (optical) pulsars but observed in X rays. -spinning neutron stars in binary systems, emitting X rays because of mass transfer onto the neutron star from its normal companion. -white dwarf stars with intense magnetic fields; the X rays are generated by flares like those on the Sun but much stronger. -black holes in binary systems, with an accretion disk around the black hole emitting X rays.
spinning neutron stars in binary systems, emitting X rays because of mass transfer onto the neutron star from its normal companion.
The Milky Way is an example of which type of galaxy? -irregular -spiral -elliptical -lenticular, S0 type
spiral
The Andromeda Galaxy (M31) is best described as a(n) -extension of the Milky Way. -gaseous nebula extending for 6° across the Earth's sky. -spiral collection of stars, dust, and gas 200,000 ly across. -vortex surrounding a black hole.
spiral collection of stars, dust, and gas 200,000 ly across.
What is photodisintegration? -splitting apart of atomic nuclei by gamma rays -destruction of a star by the pressure of the radiation inside it -ejection of a neutron or proton from an atomic nucleus, accompanied by the emission of a gamma ray -heating and ejection of mass from the surface of a normal star by the radiation from an orbiting neutron star
splitting apart of atomic nuclei by gamma rays
The four physical forces at work in the universe are gravitational, electromagnetic, strong nuclear, and weak nuclear forces. Which two of these are very short-ranged, extending over distances of only about 10^-15 m? -strong nuclear and electromagnetic forces -strong and weak nuclear forces -gravitational and electromagnetic forces -electromagnetic and weak nuclear forces
strong and weak nuclear forces
What type of object has been proposed to explain the tremendous activity detected at the center of the Milky Way Galaxy? -supermassive black hole -supernova explosion -rapidly rotating neutron star -giant molecular cloud
supermassive black hole
The diameter of a typical neutron star of 1 solar mass is predicted to be approximately -that of Earth, 12,800 km. -1 km. -that of an average city, a few kilometers. -that of the Sun.
that of an average city, a few kilometers.
The great breakthrough in understanding the nature of pulsars was - the realization that pulsars were found only in the galactic plane. -the connection between pulsars and variable stars. -the discovery of a pulsar in the middle of the Crab Nebula. -the discovery that all pulsars have periods which are multiples of a universal pulsar period.
the discovery of a pulsar in the middle of the Crab Nebula
The farther away a galaxy is, the more its light is redshifted, as observed from Earth. This relationship between redshift and distance is caused by -the gravitational redshift. Photons leaving a more distant galaxy have traveled farther through the galaxy's gravitational field, so they have lost more energy and are more redshifted. -the Doppler shift of light leaving a moving object. More distant galaxies are moving faster through space, so their light is more strongly Doppler-shifted (redshifted). -energy losses. The universe does not really expand; photons simply lose energy (wavelength lengthens) as they travel. Photons from more distant galaxies have traveled farther and so are more redshifted. -the expansion of space itself, which stretches the wavelength of the photon. The longer the time the photon has traveled, the more space has expanded and therefore the more the photon has been redshifted.
the expansion of space itself, which stretches the wavelength of the photon. The longer the time the photon has traveled, the more space has expanded and therefore the more the photon has been redshifted.
The fact that quasars can be detected from distances from which even the biggest and most luminous galaxies cannot be seen means that -they must be in directions where intergalactic absorption by dark matter is minimum, allowing us to see them. -they must be in directions where gravitational focusing by the masses of nearer galaxies makes them visible from Earth. -they must be far more luminous than the brightest galaxies. -their spectra have not been as redshifted by their motion as those of galaxies and hence they can still be seen.
they must be far more luminous than the brightest galaxies.
What does a spiral galaxy look like when seen edge-on? -thick, straight line of light with a central light bulge -thick line curved into a spiral shape -circular, with no evidence of spiral arms since they are hidden by dust and gas -thick, straight line with constant thickness
thick, straight line of light with a central light bulge
What mechanism appears to produce the double radio sources seen in intergalactic space? -two black holes orbiting around a small but massive galactic nucleus -radio-bright galaxy with a dark absorbing disk edge-on to Earth, splitting the source into two as seen from Earth -two oppositely directed jets of matter, ejected from a small source -two radio galaxies orbiting each other much like two binary stars
two oppositely directed jets of matter, ejected from a small source
In 2004 astronomers made a significant discovery which enabled them to test some of the predictions of general relativity. What was this discovery? -two neutron stars collided with each other -a neutron star with a mass more than a hundred times the mass of the Sun -a pulsar which was not precessing and, in fact, which aimed its radiation beam directly at Earth -two pulsars in orbit around each other
two pulsars in orbit around each other
Which of the following properties can never be known about a black hole? -type of material inside it -total amount of matter (the mass) inside it -angular momentum (spin) -net electric charge
type of material inside it
A quasar is now thought to be a -very luminous object at a very large distance from the Sun. -distant but very luminous and active star in the Milky Way Galaxy. -long-lived supernova explosion. -nearby star, ejected with great violence and velocity from the center of a galaxy.
very luminous object at a very large distance from the Sun.
The major surprise about Cygnus A, one of the first three sources of strong radio emission detected by Grote Reber in the late 1930s, when examined with large optical telescopes, was that it -had no corresponding optical counterpart at all. -was at the center of the Milky Way Galaxy. -was a very bright supernova remnant. -was a very distant object that was relatively faint at optical wavelengths yet extremely luminous at radio wavelengths.
was a very distant object that was relatively faint at optical wavelengths yet extremely luminous at radio wavelengths.
The famous Curtis-Shapley debate in 1920 concerned which fundamental astronomical question in astronomy? -whether all stars were like the Sun or fundamentally different -whether the Sun was at the center of the Milky Way Galaxy -whether the spiral "nebulae" were part of the Milky Way Galaxy or more distant, separate entities -whether the universe was expanding outward in all directions
whether the spiral "nebulae" were part of the Milky Way Galaxy or more distant, separate entities
When mass transfer in a binary system involves mass transferred to a white dwarf, the result is a nova. When the mass is transferred to a neutron star, the result is a(n) -soft gamma-ray repeater. -X-ray burster. -black hole. -magnetar.
x-ray burster
