Chapter 16
Compared to spiral galaxies, elliptical galaxies are A) redder and rounder. B) bluer and flattened. C) always much smaller. D) bluer and rounder. E) redder and flattened.
A
What is a quasar? A) the extremely bright center of a distant galaxy, thought to be powered by a supermassive black hole B) another name for very bright stars of spectral type O C) a star-like object that actually represents a bright patch of gas in the Milky Way D) a very large galaxy thought to be formed by the merger of several smaller galaxies, resulting in a quick burst of star formation E) the name given to the largest objects in the Kuiper Belt
A
Hubble's "constant" is constant in A) time. B) space. C) space and time. D) our Galaxy, but it is different in others.
B
What can be inferred about the distance traveled by the blob of plasma shown moving in this figure at almost the speed of light? A) It could only have moved a small fraction of a light year between 1991 and 1997. B) It moved several light years between 1991 and 1997. C) There is not enough information to tell anything about the distance traveled by the plasma.
B
What is the most accurate way to determine the distance to a very distant galaxy? A) Hubble's law B) Cepheid variables C) main-sequence fitting D) white dwarf supernova E) Stellar parallax
B
Which of the following is true about irregular galaxies? A) They are composed solely of old stars. B) They were more common when the universe was younger. C) They have significant spheroidal component. D) They have well defined spiral arms. E) They have reddish colors.
B
Which of the following types of galaxies appear reddest in color? A) irregulars B) lenticulars C) ellipticals D) spirals
C
Based on current estimates of the value of Hubble's constant, how old is the universe? A) more than 20 billion years old B) 4 to 8 billion years old C) 15 to 20 billion years old D) 12 to 15 billion years old E) 8 to 12 billion years old
D
What is Hubble's law? A) The faster a spiral galaxy's rotation speed, the less luminous it is. B) The recession velocity of a galaxy is inversely proportional to its distance. C) The faster a spiral galaxy's rotation speed, the more luminous it is. D) The recession velocity of a galaxy is directly proportional to its distance. E) The luminosity of the Cepheid variable star is directly proportional to its pulsation period.
D
What is the most accurate way to determine the distance to a nearby galaxy? A) stellar parallax B) main sequence fitting C) radar ranging D) Cepheid variables E) Hubble's law
D
What evidence supports the idea that a collision between two spiral galaxies might lead to the formation of a single elliptical galaxy? A) observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies B) observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies C) the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies D) observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy E) all of the above
E
A star that is known to be 10,000 times brighter than the sun has the same apparent brightness as a nearby G2 star. How many times further away is the bright star? A) The bright star is 10,000 times further away than the nearby G2 star. B) The bright star is 100 times further away than the nearby G2 star. C) The bright star is 10 times further away than the nearby G2 star. D) The bright star is actually a factor of 10 times closer than the nearby G2 star.
B
How was Edwin Hubble able to use his discovery of Cepheids in Andromeda to prove that the "spiral nebulae" were actually galaxies external to the Milky Way? A) There are no Cepheids in the Milky Way, so his discovery proved that Andromeda had to be in another galaxy. B) He measured the parallaxes of the Cepheids in Andromeda to determine their distances. He showed that Andromeda was far outside the Milky Way Galaxy. C) From the period-luminosity relation for Cepheids, he was able to determine the distance to Andromeda. He showed that it was far outside the Milky Way Galaxy. D) As a Cepheid is a type of luminous galaxy, Hubble's discovery of Cepheids in Andromeda proved that it was a separate galaxy from the Milky Way. E) He used main-sequence fitting to determine the distances to the Cepheids. He showed that Andromeda was far outside the Milky Way Galaxy.
C
The disk component of a spiral galaxy includes which of the following parts? A) bulge B) globular clusters C) spiral arms D) halo E) all of the above
C
Which of the following types of galaxies have a disk and spheroidal component but lack spiral arms? A) irregulars B) ellipticals C) lenticulars D) all of the above
C
If we represent the Milky Way Galaxy as the size of a grapefruit, the distance to the Andromeda Galaxy would be about A) 300 km. B) 3 m. C) 3 km. D) 3 cm. E) 30 m.
B
What is the major difference between an elliptical galaxy and a spiral galaxy? A) Elliptical galaxies are not as big as spiral galaxies. B) An elliptical galaxy lacks a disk component. C) A spiral galaxy contains mostly younger stars. D) A spiral galaxy has a spherical halo. E) There are no dwarf spiral galaxies, but there are dwarf ellipticals.
B
What two quantities did Edwin Hubble compare for a sample of galaxies to discover the expansion of the universe? A) age and distance B) velocity and distance C) luminosity and distance D) luminosity and temperature E) velocity and temperature
B
Dr. X believes that the Hubble constant is H0 = 20 km/s/Mly while Dr. Y believes it is H0 = 24km/s/Mly. Which statement below automatically follows? A) Dr. X believes that the universe is older than Dr. Y believes. B) Dr. X believes that the universe will someday stop expanding, while Dr. Y believes it will expand forever. C) Dr. X believes that the universe is expanding, but Dr. Y does not. D) Dr. X believes that the Andromeda Galaxy (a member of our Local Group) is moving away from us at a slower speed than Dr. Y believes. E) Dr. X believes that the universe has a much higher density than Dr. Y believes.
A
I observe a galaxy that is 100 million light years away. Which of the following do I see? A) the light from the galaxy as it was 100 million years ago, and it is redshifted B) the light from the galaxy as it is today, and it is redshifted C) the light from the galaxy as it is today, and it is blueshifted D) the light from the galaxy as it was 100 million years ago, and it is blueshifted E) Nothing: the galaxy lies beyond the cosmological horizon.
A
If an object doubles its luminosity in 10 hours, how large can the emitting source of light be? A) about 10 light-hours across B) about 10 parsecs across C) about 10 light-years across D) varies depending on how luminous the object is E) varies depending on how far away the object is
A
In the 1960s, Maarten Schmidt determined that quasars were very distant objects by A) determining their redshifts. B) determining their parallax angles. C) determining how luminous they were. D) discovering that they were embedded in distant galaxies. E) determining how small the source of light was from its luminosity variations.
A
Most active galactic nuclei are at large distances from us;relatively few nearby galaxies harbor active galactic nuclei . What does this imply? A) Active galactic nuclei tend to become less active as they age. B) Active galactic nuclei can form only at large distances from the Milky Way. C) The jets seen in many active galactic nuclei must cause them to move far away from us. D) Massive black holes existed only when the universe was young and no longer exist today.
A
Scale the Milky Way down to the size of a compact disc. Which of the following best describes the size, shape, and distance of the Andromeda Galaxy on the same scale? A) a compact disk a few meters away B) a grapefruit a few meters away C) a grapefruit about 1 kilometer away D) a compact disk about the length of a football field away E) a pecan nut about 1 centimeter away
A
What is a central dominant galaxy? A) a giant elliptical galaxy at the center of a dense cluster B) a giant spiral galaxy that exerts large tidal forces on other nearby galaxies C) a galaxy around which many other smaller galaxies orbit D) a hypothesized galaxy type that no longer exists but once dominated the structure of the universe E) a spiral galaxy from which many smaller galaxies form when it is stripped apart by tidal forces
A
What is the most accurate way to determine the distance to a nearby star? A) stellar parallax B) Hubble's law C) radar ranging D) Cepheid variables E) main-sequence fitting
A
Which types of galaxies have a clearly defined disk component? A) spirals and lenticulars B) spirals only C) ellipticals only D) irregulars only E) lenticulars only
A
Why can't we see past the cosmological horizon? A) Beyond the cosmological horizon, we are looking back to a time before the universe had formed. B) The cosmological horizon is infinitely far away, and we can't see to infinity. C) We do not have telescopes big enough. D) We do not have detectors sensitive enough. E) The universe extends only to this horizon.
A
Why do we believe that starburst galaxies represent a temporary stage in galaxy evolution? A) Such galaxies form stars at such a high rate that they would have consumed all their gas long ago if they had always been forming stars at this high rate. B) All starburst galaxies look like normal spiral galaxies, aside from the starbursts. C) We observe starbursts to last only a few years at a time. D) We don't see any nearby starburst galaxies.
A
Why is the Hyades Cluster important for building up a catalog of the true luminosities of main-sequence stars? A) It is close enough to us that the distance to its stars can be found by stellar parallax. B) It is an extremely bright star cluster. C) It's a cluster that has been photographed over many decades, so we know how the stars vary in brightness. D) It contains many Cepheid variable stars that can be used to determine its distance. E) It is an old globular cluster whose age we can determine very accurately by measuring its main-sequence turn-off point.
A
How do astronomers use the Hubble Constant (H0) to estimate the age of the universe? A) The age of the universe is about 600 million times H0. B) The inverse of H0 is the approximate age of the universe. C) They do not. The age of the universe is unknowable.
B
How do observations of galaxies at different distances help us learn about galaxy evolution A) We can observe galaxies at different distances merge, helping us learn how mergers affect evolution. B) Observations of different distances show galaxies of different ages and therefore different stages of evolution. C) We can see what our galaxy used to look like over time, helping us theorize about the physical processes that led to its current appearance. D) We can observe the evolution of a single galaxy over time. E) Observations of the most distant galaxies will allow us to observe the birth of galaxies.
B
How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced? A) by nuclear fusion near a central black hole B) by gravity, which converts the potential energy of matter falling toward a central black hole into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter C) by matter-antimatter annihilation near a central black hole D) by magnetic fields that trap and accelerate charged particles, which then radiate large amounts of energy E) by matter that has been converted to pure energy by interacting with the jets shot out by a central black hole
B
How many more stars does a starburst galaxy form, in one year, than the Milky Way? A) about a thousand B) about a hundred C) about ten D) a few E) about the same, but it does so for much longer
B
Suppose we observe a source of X-rays that varies substantially in brightness over a period of a few days. What can we conclude? A) We must be seeing the rapid orbit of two stars in a binary system. B) The X-ray source can be no more than a few light-days in diameter. C) The X-ray source must have a strong, rapidly varying magnetic field. D) The X-ray source must contain a black hole with an accretion disk. E) The X-ray source must be a quasar.
B
This figure shows the Cepheid period-luminosity relation. A Cepheid star with a period of 30 days has the same apparent brightness as a nearby G2 star. How many times further away is the Cepheid star? A) The Cepheid star is 10,000 times further away than the nearby G2 star. B) The Cepheid star is 100 times further away than the nearby G2 star. C) The Cepheid star is 10 times further away than the nearby G2 star. D) The Cepheid star is actually a factor of 10 times closer than the nearby G2 star.
B
What is a standard candle? A) a class of objects that we know all have exactly the same luminosity B) an object for which we are likely to know its true luminosity C) an object for which we can easily measure its apparent brightness D) any star for which we know its exact apparent brightness E) a unit of luminosity used by astronomers
B
What is the current limit to distances we can measure via parallax, until the results of the new Gaia mission become available? A) about 100,000 light years B) about 1000 light years C) about 100 light years D) about 10,000 light years
B
Which of the following is not a strong argument for the theory that some large elliptical galaxies formed as the result of galaxy collisions? A) Elliptical galaxies dominate the population in dense galaxy clusters. B) Galaxy collisions are common and most galaxies in the universe are elliptical. C) Computer simulations predict that the product of a galaxy collision is generally an elliptical galaxy. D) Some ellipticals have stars and gas that rotate opposite to the rest of the galaxy. E) Some elliptical galaxies are surrounded by shells of stars.
B
Why are Cepheid variables important? A) Cepheids variables are a type of irregular galaxy, much more common in the early universe. Therefore they help to understand how galaxies formed. B) Cepheids variables are pulsating stars whose pulsation periods are directly related to their true luminosities. Therefore they can be used as distance indicators. C) Cepheids variables are supermassive stars that are on the verge of becoming supernovae. Therefore they allow us to choose candidates to watch if we hope to observe a supernova. D) Cepheid variables are stars that vary in brightness because they harbor a black hole. Therefore, they provide direct evidence for black holes.
B
Approximately how many stars does a dwarf elliptical galaxy have? A) 10 billion B) less than a million C) less than a billion D) 1 trillion E) 100 billion
C
Based on counting the number of galaxies in a small patch of the sky and multiplying by the number of such patches needed to cover the entire sky, the total number of galaxies in the observable universe is estimated to be approximately A) 10 billion. B) 100 million. C) 100 billion. D) 1 trillion. E) 1 billion.
C
How did Edwin Hubble measure the distance to the Andromeda Galaxy? A) He applied main-sequence fitting to star clusters in Andromeda. B) He measured its redshift and applied Hubble's Law. C) He applied the period-luminosity relation to Cepheid variables in Andromeda. D) He detected white dwarf supernovae in Andromeda. E) He measured its parallax.
C
Most large galaxies in the universe are A) abnormal. B) irregular C) spiral or lenticular. D) elliptical
C
Recall that Hubble's law is written v = H0d, where v is the recession velocity of a galaxy located a distance d away from us, and H0 is Hubble's constant. Suppose H0 = 20 km/s/Mly. How fast would a galaxy 1000 Mly distant be receding from us? A) 50 km/s B) 0.20 times the speed of light C) 20,000 km/s D) 20 km/s E) 20 Mly/s
C
This figure shows Hubble's law. If a galaxy is observed to be moving away from us at 30,000 km/s, how far away is it? A) about 5000 million light-years C) about 1400 million light-years B) about 30,000 light-years D) about 900 million light-years
C
This figure shows the Cepheid period-luminosity relation. What is the approximate luminosity of a Cepheid star that varies in brightness on a 10 day cycle? A) about 1000 times the luminosity of the sun B) about 30,000 times the luminosity of the sun C) about 3000 times the luminosity of the sun D) about 10,000 times the luminosity of the sun
C
Where are the X-rays produced that are emitted by quasars and other active galactic nuclei? A) in fast-moving jets of electrons that are ejected from the active galactic nucleus B) in an ionization nebulae of interstellar gas surrounding the accretion disk C) in the hot gas in an accretion disk around a central black hole D) in dust grains in molecular clouds that encircle the active galactic nucleus E) all of the above
C
Which of the following cannot be true of the very first stars formed in the universe? A) Some may have formed singly, in isolation from one another. B) Some may have formed in large clusters. C) Some may have had rocky planets around them. D) Some may have all exploded as supernovae by now. E) Some may still exist in the Milky Way today.
C
Which of the following is a consequence of Hubble's Law? A) The closer a galaxy is to us, the faster it moves away from us. B) More distant galaxies appear younger. C) The more distant a galaxy is from us, the faster it moves away from us. D) The Big Bang E) All galaxies are moving away from us equally fast.
C
Which of the following is not a good reason why white-dwarf supernovae are good standard candles for distance measurements? A) All white-dwarf supernovae involve the explosion of stars of nearly the same mass. B) White-dwarf supernovae are so bright that they can be detected even in very distant galaxies. C) White-dwarf supernovae occur only among young and extremely bright stars. D) White-dwarf supernovae are common enough that we detect several every year. E) All white-dwarf supernovae have similar light curves, which makes them easy to distinguish from massive-star supernovae.
C
Which of the following processes slowed the collapse of protogalactic clouds? A) the pull of gravity of the mass of the cloud material B) the radiating away of thermal energy C) the shock waves from the exploding supernovae of the earliest stars D) the formation of the first generation of stars E) the conversion of gravitational potential energy into kinetic and thermal energy as the cloud collapsed
C
Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy? A) a very low-density cloud with very little angular momentum B) a low-density cloud with quite a bit of angular momentum C) a dense cloud with very little angular momentum D) a very massive cloud with any density and a lot of angular momentum E) a dense cloud with quite a bit of angular momentum
C
Which of these statements about Hubble's classification scheme for galaxies is false? A) Low numbered elliptical galaxies are rounder than high numbered elliptical galaxies. B) It includes two broad types of spiral galaxies. C) It represents an evolutionary sequence for galaxies (e.g., type SBa galaxies slowly turn into type SBb). D) Sc galaxies have smaller bulges and more dusty gas than Sa galaxies.
C
How does a lenticular galaxy differ from a normal spiral galaxy? A) It is flatter in shape. B) It has no bulge. C) It has an elongated bulge resembling a bar more than a sphere. D) It has no spiral arms. E) It has no gas or dust.
D
Suppose that we look at a photograph of many galaxies. Assuming that all galaxies formed at about the same time, which galaxy in the picture is the youngest? A) the one that is closest to us B) the one that is reddest in color C) the one that is bluest in color D) the one that is farthest away E) the one that appears smallest in size
D
Which of the following gives the two main assumptions of theoretical models of galaxy evolution? A) The universe was composed originally only of hydrogen, and all the other elements came from stars. B) The beginning of the universe is modeled after a supernova explosion, and all elements were produced by this exploding star. C) Hydrogen and helium filled all of space, and the entire universe had exactly the same density everywhere. D) Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others. E) The universe has always been expanding, and denser areas contracted to form the first stars.
D
Which of the following is not a piece of evidence supporting the conclusion that active galactic nuclei are powered by accretion disks around massive black holes? A) Radio observations sometimes show long jets of material that can extend millions of light-years out from the galactic center. B) Observed radiation from the galactic center can vary significantly in brightness in times as short as a few days. C) Spectral lines from the galactic center indicate that clouds of gas are orbiting a central object at very high speed. D) Infrared observations show that many stars are forming near the centers of active galaxies. E) The total amount of radiation coming from the galactic center can, in some cases, exceed 100 times the total luminosity of the Milky Way Galaxy.
D
Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy? A) The higher density of gas has a stronger force of gravity, and therefore the cloud collapses more quickly. B) The thickness of the dense cloud prevents a disk from forming. C) The more frequent collisions between particles randomize the particle orbits. D) The higher gas density forms stars more efficiently, so all the gas is converted into stars before a disk can form. E) The force of gravity can pull the material into a more spherical shape.
D
In this picture, we are seeing light from the circled elliptical galaxy (HUDF-JD2) from when the universe was only about 800 million years old. The spiral galaxy below it is much closer. Why does HUDF-JD2 appear a deep red, compared to the whitish color of the nearby spiral? A) Thick dust from active star formation blocks all the blue light, only letting red light escape. B) At such a large distance, all the light emitted by it is very redshifted. C) Even at this young age, the galaxy contains few high mass blue stars. D) AandB E) B and C
E
What makes white-dwarf supernovae very good standard candles for distance measurements? A) They are very bright, so they can be used to determine the distances to galaxies billions of light-years away. B) They should all have approximately the same luminosity. C) We have had several occur close to us in the Milky Way, so we have been able to determine their luminosities very accurately. D) They occur so frequently that we can use them to measure the distances to virtually all galaxies. E) both A and B
E
Which of the following is evidence for supermassive black holes in active galaxies? A) quasars emitting approximately equal power at all wavelengths from infrared to gamma rays B) the very high speeds of gas orbiting around the galactic nucleus C) the discovery of powerful jets coming from a compact core D) rapid changes in the luminosity of the galaxy nucleus E) all of the above
E
Which of the following is not true of quasars? A) Some quasars can change their brightness on the timescale of hours. B) Quasars were more common in the past. C) Some quasars are more than a thousand times more luminous than the Milky Way. D) The light produced by quasars comes from an accretion disk surrounding a supermassive black hole. E) Quasars are powered by the intense production of large numbers of stars that can only be sustained for a relatively short time.
E
Which types of galaxies have a clearly defined spheroidal component? A) ellipticals only B) irregulars only C) lenticulars only D) spirals only E) all but irregulars
E
Why do elliptical galaxies appear yellow or red? A) They contain no hot, young blue stars B) They contain only massive-stars that have progressed to the red-giant stage C) They have very little dust or cool gas, and thus have little ongoing star formation D) AandB E) A and C
E
Why should galaxy collisions have been more common in the past than they are today? A) Galaxies were more active in the past and therefore would have collided with each other more frequently. B) Galaxies attracted each other more strongly in the past because they were more massive; they had not yet turned most of their mass into stars and light. C) Galaxies were much bigger in the past because they had not contracted completely. D) Galaxy collisions shouldn't have been more common in the past than they are now. E) Galaxies were closer together in the past because the universe was smaller.
E
