Testbank - The Cosmic Perspective

The Cosmic Perspective, 7e (Bennett et al.) Chapter 21 Galaxy Evolution

21.1 Multiple-Choice Questions 1) How do observations of distant galaxies help us learn about galaxy evolution !) "bservations at different distances show galaxies of different ages and therefore different stages of evolution. #) $e can observe the birth of galaxies. C) $e $e can observe the evolution of a single galaxy over ti%e. &) $e can observe two galaxies %erging and what the result is' helping us learn how %ergers affect evolution. () $e can see what our galaxy used to loo lie and therefore theori*e about the physical processes that led to its current appearance. !nswer+ ! 2) $hy are telescopes so%eti%es called ,ti%e %achines, !) because the author' H.. $ells' $ells' used the ter% to describe telescopes in a boo #) because so%e of the oldest telescopes are still in use today C) because observations of distant obects reveal the% as they were in the past &) because astrono%ers can use telescopes to see the Mily $ay $ay as it was when it was %uch younger () /t0s a ournalistic %isno%er+ you cannot travel into the past or the future. !nswer+ C ) / observe a galaxy that is 1 %illion light-years away+ what do / see !) the light fro% the galaxy as it is today' but it is blueshifted #) the light fro% the galaxy as it is today' but it is redshifted C) the light fro% the galaxy as it was 1 %illion years ago and it it blueshifted &) the light fro% the galaxy as it was 1 %illion years ago and it is redshifted () 3othing+ the galaxy lies beyond the cos%ological hori*on. !nswer+ & 4) $hich of the following gives the two %ain assu%ptions of theoretical %odels of galaxy evolution !) 5he beginning of the universe is %odeled after a supernova explosion' and all the ele%ents were produced in the proper 6uantities by the star. #) Hydrogen and heliu% filled all of space' and certain regions of the universe un iverse were slightly denser than others. C) Hydrogen and heliu% filled all of space' and all the universe was exactly the sa%e density. &) 5he universe has always been expanding' and denser areas contracted to for% the first stars. () 5he universe was co%posed originally only of hydrogen' and all the other ele%ents ca%e fro% stars. !nswer+ #

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Copyright 7 214 8earson (ducation' /nc.

9) $hich of the following processes slowed the collapse of protogalactic clouds !) the for%ation of the first generation of stars #) the conversion of gravitational potential energy into inetic and ther%al energy as the cloud collapsed C) the shoc waves fro% the exploding supernovae of the earliest stars &) the pull of gravity of the %ass of the cloud %aterial () the radiating away of ther%al energy !nswer+ C :) $hich of the following types of protogalactic clouds is %ost liely to for% an elliptical galaxy !) a very low-density cloud with very little angular %o%entu% #) a dense cloud with very little angular %o%entu% C) a low-density cloud with 6uite a bit of angular %o%entu% &) a dense cloud with 6uite a bit of angular %o%entu% () a very %assive cloud with any density and a lot of angular %o%entu% !nswer+ # ;) $hy is a dense cloud %ore liely to produce an elliptical galaxy than a spiral galaxy !) 5he higher density of gas has a stronger force of gravity' and therefore the cloud collapses %ore 6uicly. #) 5he force of gravity can pull the %aterial into a %ore spherical shape. C) 5he %ore fre6uent collisions between particles rando%i*e the particle orbits. &) 5he thicness of the dense cloud prevents a dis fro% for%ing. () 5he higher gas density for%s stars %ore efficiently' so all the gas is co nverted into stars before a dis can for%. !nswer+ ( <) $hat evidence supports the theory that elliptical galaxies co%e fro% denser clouds !) (lliptical galaxies are denser than spiral galaxies. #) (lliptical galaxies are generally larger than spiral galaxies. C) (lliptical galaxies at high redshifts lac young' blue stars. &) (lliptical galaxies have %ore gas than spiral galaxies. () (lliptical galaxies have denser stars than spiral galaxies. !nswer+ C =) /f we represent the Mily $ay alaxy as the si*e of a grapefruit >1-c% dia%eter)' the distance to the !ndro%eda alaxy would be about !) 1 c%. #)  %. C)  %. &) 1 %. () 1 %. !nswer+ #

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1) $hy should galaxy collisions have been %ore co%%on in the past than they are today !) alaxies were %ore active in the past and therefore would have collided with each other %ore fre6uently. #) alaxies were %uch bigger in the past since they had not contracted co%pletely. C) alaxies were closer together in the past bec ause the universe was s%aller. &) alaxies attracted each other %ore strongly in the past because they were %ore %assive? they had not yet turned %ost of their %ass into stars and light. () alaxy collisions shouldn0t have been %ore co%%on in the past than they are now. !nswer+ C 11) $hat evidence supports the idea that a collision between two spiral galaxies %ight lead to the creation of a single elliptical galaxy !) observations of so%e elliptical galaxies surrounded by shells of stars that probably for%ed fro% stars stripped out of s%aller galaxies #) the fact that elliptical galaxies do%inate the galaxy populations at the cores of dense clusters of galaxies C) observations of so%e elliptical galaxies with stars and gas clouds in their cores that orbit differently fro% the other stars in the galaxy &) observations of giant elliptical galaxies at the center of d ense clusters that %ay have grown by consu%ing other galaxies () all of the above !nswer+ ( 12) $hich of the following is not a strong argu%ent for the theory that so%e large elliptical galaxies for%ed as the result of galaxy collisions !) (lliptical galaxies do%inate the population in dense galaxy clusters. #) @o%e ellipticals have stars and gas that rotate o pposite to the rest of the galaxy. C) @o%e elliptical galaxies are surrounded by shells of stars. &) Co%puter si%ulations predict that the product of a g alaxy collision is generally an elliptical galaxy. () alaxy collisions are co%%on and %ost galaxies in the universe are elliptical. !nswer+ ( 1) $hat is a central dominant galaxy !) a galaxy around which %any other s%aller galaxies orbit #) a giant spiral galaxy that exerts large tidal forces on o ther nearby galaxies C) a spiral galaxy fro% which %any s%aller galaxies for% when it is stripped apart by tidal forces &) a giant elliptical galaxy at the center of a dense cluster () a hypothesi*ed galaxy type that no longer exists but once do%inated the structure of the universe !nswer+ &

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14) How %any %ore stars does a starburst galaxy for%' in one year' than the Mily $ay !) a few #) about ten C) about a hundred &) about a thousand () about the sa%e' but it does so for %uch longer !nswer+ C 19) $hy do we believe that starburst galaxies represent a te%porary stage in galaxy evolution !) $e observe starbursts to last only a few years at a ti%e. #) @uch galaxies produce so %uch light that they would have consu%ed all their gas long ago if they had always been for%ing stars at this high rate. C) $e don0t see any nearby starburst galaxies. &) !ll starburst galaxies loo lie nor%al spiral galaxies' aside fro% the starbursts. !nswer+ # 1:) @tarburst galaxies produce %ost of their light in the wavelength range of !) A rays. #) the ultraviolet. C) the visible. &) the infrared. () all wavelengths. !nswer+ & 1;) $hat evidence suggests that s%all galaxies in our Bocal roup have undergone two or %ore starbursts in the past !) $e observe several s%all galaxies currently undergoing %assive star for%ation. #) $e see s%all galaxies in which %any stars have one age and %any others have another age that is billions of years older. C) $e see evidence that s%all galaxies in our Bocal roup have experienced several collisions in the past. &) $e see evidence that several s%all galaxies were shot o ut of larger galaxies in our Bocal roup during an age of starburst activity. () $e do not have any evidence that galaxies in our Bocal roup were once starburst galaxies. !nswer+ # 1<) /n the 1=:s' Maarten @ch%idt deter%ined that 6uasars were very distant obects by !) deter%ining how lu%inous they were. #) deter%ining how s%all the source of light was fro% its variations in lu%inosity. C) discovering that they were e%bedded in distant galaxies. &) deter%ining their redshifts. () deter%ining their parallax angles. !nswer+ &

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1=) $hat is a quasar  !) a starlie obect that actually represents a bright patch of gas in the Mily $ay #) a very large galaxy thought to be for%ed by the %erger of several s%aller galaxies' typically found in the center of a galaxy cluster C) a speciali*ed astrono%ical instru%ent for observing distant stars &) the extre%ely bright center of a distant galax y' thought to be powered by a %assive blac hole () another na%e for very bright stars of spectral type " !nswer+ & 2) $hich of the following is not true of 6uasars !) @o%e 6uasars are %ore than a thousand ti%es %ore lu%inous than the Mily $ay. #) Quasars were %ore co%%on in the past. C) Quasars are powered by the energy radiated by %atter falling into a central blac hole. &) Quasars are powered by the intense production of large nu%bers of stars that can only be sustained for a relatively short ti%e. () @o%e 6uasars can change their brightness every few hours. !nswer+ & 21) $hich of the following is evidence for super%assive blac holes in active galaxies !) the discovery of powerful ets co%ing fro% a c o%pact core #) rapid changes in the lu%inosity of the galaxy nucleus C) 6uasars e%it approxi%ately e6ual power at all wa velengths fro% infrared to ga%%a rays &) very high speed orbital %otions around galactic nuclei () all of the above !nswer+ ( 22) 5he %ost active galactic nuclei are usually found at large distances fro% us? relatively few nearby galaxies have active galactic nuclei. $hat does this i%ply !) Massive blac holes existed only when the universe was young and no longer exist today. #) !ctive galactic nuclei tend to beco%e less active as they age. C) !ctive galactic nuclei can for% only at large distances fro% the Mily $ay. &) 5he ets seen in %any active galactic nuclei %ust cause the% to %ove far away fro% us. !nswer+ # 2) $hat is a galactic wind  !) a et of ioni*ed particles shot out of a starburst galaxy #) hot gas erupting into intergalactic space fro% a large superbubble C) the heat >infrared radiation) e%itted by dust grains in the large %olecular clouds of starburst galaxies &) the cooler gas pushed out of a starburst galaxy by the intense radiation pressure () a wind created by the expansion of the universe that can %ove galaxies around !nswer+ #

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24) /f an obect doubles its lu%inosity in 1 hours' how large can the e%itting source of light be !) about 1 light-years across #) about 1 parsecs across C) about 1 light-hours across &) varies depending on how lu%inous the obect is () varies depending on how far away the obect is !nswer+ C 29) @uppose we observe a source of A rays that varies substantially in brightness over a period of a few days. $hat can we conclude !) 5he A-ray source is a 6uasar. #) 5he A-ray source contains a blac hole with an accretion dis. C) 5he A-ray source is no %ore than a few light-days in dia%eter. &) 5he A-ray source %ust have a strong' rapidly v arying %agnetic field. () $e are seeing the rapid orbit of two stars in a binary syste%. !nswer+ C 2:) $hich of the following is not a piece of evidence supporting the conclusion that active galactic nuclei are powered by accretion diss around %assive blac holes !) "bserved radiation fro% the galactic center varies significantly in brightness in ti%es as short as a few days. #) /nfrared observations show that %any stars are for%ing near the cen ters of active galaxies. C) adio observations so%eti%es show long ets of %aterial extending %illions of light-years out fro% the galactic center. &) 5he total a%ount of radiation co%ing fro% the galactic center is' in so%e cases' co%parable to the a%ount of radiation put out by 1 billion or %ore ordinary stars. () @pectral lines fro% the galactic center indicate that clouds of gas are orbiting a central obect at very high speed. !nswer+ # 2;) How is the energy that powers radio galaxies' 6uasars' and other active galactic nuc lei produced !) by nuclear fusion near a central blac hole #) by %agnetic fields that trap and accelerate charged particles' which then radiate high a%ounts of energy C) by %atter that has been converted to pure energy being shot out as ets by a central blac hole &) by gravity' which converts potential energy of %atter falling toward a central blac hole into inetic energy' which is then converted to ther%al energy by collisions a%ong the particles of %atter () by %atter-anti%atter annihilation near a central blac hole !nswer+ &

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2<) $here are the A rays produced that are e%itted by 6uasars and other active galactic nuclei !) in hot gas in an accretion dis around a central blac hole #) in ioni*ation nebulae of interstellar gas that surround the accretion dis C) in dust grains in %olecular clouds that encircle the active galactic nucleus &) in fast-%oving electrons that et fro% the active galactic nu cleus () all of the above !nswer+ ! 2=) How do we now that there are intergalactic clouds between a distant 6uasar and us !) $e see hydrogen e%ission lines at redshifts s%aller than that of the 6uasar. #) $e see hydrogen absorption lines at redshifts s%aller than that of the 6uasar. C) $e see hydrogen e%ission lines at redshifts greater than that of the 6uasar. &) $e see hydrogen absorption lines at redshifts greater than that of the 6uasar. () $e see that the e%ission lines fro% the 6uasar are lessened b y intervening gas and dust. !nswer+ # ) $hat are the typical features seen in 6uasar absorption lines of intergalactic clouds !) 5he hydrogen line is wider and lines fro% he avy ele%ents are weaer at higher redshifts. #) 5he hydrogen line is narrower and lines fro% heav y ele%ents are weaer at higher redshifts. C) 5he hydrogen line is wider and lines fro% heav y ele%ents are stronger at higher redshifts. &) 5he hydrogen line is narrower and lines fro% heav y ele%ents are stronger at higher redshifts. () ! few wea absorption lines are always seen at higher redshift than the 6uasar. !nswer+ ! 1) $hich of the following cannot be true of the very first stars for%ed in the Dniverse !) 5hey %ay have all exploded as supernovae by now. #) 5hey %ay have for%ed in large clusters. C) 5hey %ay have for%ed singly' in isolation. &) @o%e %ay still exist in the Mily $ay today. () 5hey %ay have had rocy planets around the%. !nswer+ ( 2) !ll of the following are true. $hich of these gives evidence that 6uasars were %ore co%%on in the early stages of the universe !) 5hey are %ore co%%on at very great distances. #) 5hey are very bright. C) 5hey are active galactic nuclei. &) $e don0t see the% in every galaxy. !nswer+ !

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21.2 5rueEFalse Questions 1) alaxies at very large distances fro% the Mily $ay often loo distorted. !nswer+ 5D( 2) ! protogalactic cloud with slow star for%ation is %ore liely to for% a spiral galaxy than an elliptical galaxy. !nswer+ 5D( ) ! protogalactic cloud with very little angular %o%entu% is %ore liely to for% an elliptical galaxy than a spiral galaxy. !nswer+ 5D( 4) alaxy collisions were %ore co%%on in the past. !nswer+ 5D( 9) alaxy %ergers tae hundreds of %illions of years to co%plete. !nswer+ 5D( :) 5he collision of two spiral galaxies will liely result in a single giant spiral galaxy. !nswer+ F!B@( ;) @o%e galaxies in the Bocal roup stopped for%ing stars for several billion years but then started again. !nswer+ 5D( <) @tarburst galaxies produce %ost of their light in the infrared. !nswer+ 5D( =) Quasars radiate %ost of their energy as radio e%ission. !nswer+ F!B@( 1) "bservations of 6uasar absorption lines show that intergalactic clouds were %ore co%%on in the past. !nswer+ 5D(

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21. @hort !nswer Questions 1) ive exa%ples de%onstrating the role of ,nature, and ,nurture, in galaxy evolution. !nswer+ alaxies co%e in a wide variety of shapes and si*es. 8rotogalactic clouds that had low angular %o%entu% %ay have for%ed spheroidal stellar syste%s >elliptical galaxies)' while clouds with higher angular %o%entu% would have collapsed to a %ore dislie for% >spiral galaxies). @uch differences in the initial conditions is an exa%ple o f the role of nature in galaxy evolution. !n exa%ple of nurture is a collision between two spiral galaxies that rando%i*es the ordered stellar orbits' co%presses the gas and causes it to rapidly for% stars' eventually producing a gas-free' elliptical galaxy. 2) #riefly explain why starburst galaxies appear fairly ordinary when they are observed in visible light but extraordinary when they are observed in infrared light. !nswer+ @tarburst galaxies are filled with star-for%ing %olecular clouds' which contain dust grains that absorb %ost of the visible light produced by the young stars. 5his radiation heats the dust grains to very high te%peratures' and they re-e%it all the absorbed energy as infrared light. ) (xplain why galaxy interactions are far %ore co%%on than star-star interactions. !nswer+ alaxies are %uch closer together' relative to their si*e' than stars are. /f the @un were %ade the si*e of a grapefruit' the nearest star would be on the other side of the continent. However' if the Mily $ay >or any other galaxy) were %ade the si*e of a grapefruit' there would liely be another galaxy within a few feet of it. 5hus' galaxy interactions are far %ore co %%on than star-star interactions and %ust be taen into account when considering galaxy evolution. 4) $hy do spiral galaxy %ergers often trigger starbursts !nswer+ 5he dusty %olecular clouds in spiral galaxies collide during a %erger. 5he collision transfers angular %o%entu% fro% the inner%ost gas clouds to the outer p arts of the galaxies' which allows the inner clouds to %igrate toward a co%%on center. Huge a%ounts of dense clouds co%e together' resulting in a %assive burst of star for%ation. 9) How does a starburst end $hat %ight happen to the galaxy afterwards !nswer+ ! starburst %ight end by si%ply using up all the available gas to for% stars or it %ay end by the co%bined effect of %any supernovae driving a wind that blows all the gas out of the galaxy. 5he galaxy will then age' with old stars dying but no new stars for%ing until enough gas has accu%ulated' either fro% the re%nants of old stars or by gas falling bac into the galaxy. 5he halt in star for%ation can be billions of years. :) ive several observations supporting the idea that the high redshifts of 6uasars really do i%ply great distances. !nswer+ >a) $e see %any 6uasars with high redshifts' but none with blueshifts. >b) /%ages show that 6uasars are e%bedded in the centers of extre%ely distant galaxies. >c) @o%e 6uasars have been observed to be %e%bers of distant galaxy clusters. >d) $e see absorption lines produced by intergalactic gas between the 6uasar and us. >e) $e have observed a progression of other active galaxies' with those farther away being %ore active and closer ones being less active.

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;) How are the ets produced by radio galaxies si%ilar to those fro% protostars !nswer+ Gets in radio galaxies and in protostars %ay be generated by the sa%e physical %echanis%s. 5hey both probably are %eans for the syste%s to shed angular %o%entu%. 5hey both probably coexist with a dis structure. <) How do ets produced by radio galaxies differ fro% those of protostars !nswer+ Gets in radio galaxies differ fro% those in protostars in si*e and energy output. 5he centers of radio galaxies are thought to be blac holes' while the protostellar dis is orbiting a physical star with an actual surface. =) #riefly explain how we thin 6uasars produce so %uch energy. !nswer+ 5he energy is produced in the accretion dis around a super%assive blac hole. 1) $hat infor%ation about protogalactic gas clouds is contained in 6uasar absorption lines !nswer+ Quasar absorption lines show the presence of %assive clouds of neutral hydrogen between us and the 6uasar. 5he hydrogen absorption line is generally wider for higher redshifts' indicating that the %ost distant clouds are %ore %assive than the older' closer clouds' which have' presu%ably' converted so%e of their gas to stars. 5he absorption lines of heavier ele%ents are stronger' however' at lower redshift' suggesting that the older' closer galaxies have enriched their interstellar %ediu% %ore than the %ore distant' younger obects. 11) Process of Science+ $hat evidence do scientists have that super%assive blac h oles exist !nswer+ "bservations of orbiting stars and gas clouds in galaxies show that they are orbiting extre%ely %assive >tens of %illions of solar %asses) obects that are invisible. 12) Process of Science: (xplain how we can use telescopes as ti%e %achines to directly test theories of galaxy for%ation. !nswer+ 5elescopes see obects as they were when the light left the%. For distant obects' this ,loobac ti%e, can be billions of years and we can literally see galaxies in the process of for%ation. /n this way' we can directly test theories for how they for%. 1) Process of Science: /n the discovery of 6uasars' the radio source C2; was found to have strong e%ission lines at wavelengths that did not correspond to any nown ele%ent on (arth. @uppose a scientist postulated that they had discovered a new ele%ent that only existed in these powerful radio sources. How would you test this !nswer+ ou would expect to see the sa%e lines in other galaxies or radio sources lie C2;. >5his is not seen I instead' a si%ilar pattern of lines is seen b ut shifted in wavelength.)

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21.4 Mastering !strono%y eading Qui* 1) 5elescopes being planned for the study of the earliest stages in galactic lives will be opti%i*ed for observations in !) visible light. #) infrared light. C) radio waves. &) A rays. !nswer+ # 2) $hich of the following is an i%portant starting assu%ption in %odels of galaxy for%ation !) alaxies for% first' then blac holes. #) !ll galaxies start out as spiral galaxies. C) #lac holes for% first' seeding the for%ation of galaxies. &) @o%e regions in the universe start out den ser than others. !nswer+ & ) !ccording to observations' what type of galaxy was %uch %ore co%%on when the universe was 2 billion years old than it is today !) elliptical galaxies #) spiral galaxies C) irregular galaxies &) $e can0t say' because we are living at a ti%e when the u niverse is 14 billion years old' not 2 billion years. !nswer+ C 4) Collisions between galaxies typically unfold over a period of !) several days. #) several %onths. C) thousands of years. &) hundreds of %illions of years. !nswer+ & 9) $hy are collisions between galaxies %ore liely than collisions between stars within a galaxy !) elative to their si*es' galaxies are closer together than stars. #) alaxies are %uch larger than stars. C) alaxies travel through space %uch faster than stars. &) alaxies have higher redshifts than stars. !nswer+ !

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:) Current understanding holds that a galaxy0s type >spiral' elliptical' or irregular) !) is always deter%ined by the angular %o%entu% of the protogalactic cloud that for%ed it. #) %ay either be the result of conditions in the protogalactic cloud that for%ed it or the result of later interactions with other galaxies. C) is deter%ined by whether the galaxy is located in a cluster where collisions are liely or outside a cluster where collisions are less liely. &) %ay either be a result of the %ass of the protogalactic cloud that for%ed it or the result of the heavy ele%ent abundance in that cloud. !nswer+ # ;) $hich of the following features is not a feature of central dominant galaxies !) 5hey0re found in clusters of galaxies. #) 5hey are often spiral galaxies. C) 5hey often have %ultiple galactic nuclei nea r their centers. &) 5hey are thought to for% by the %erger of several s%aller galaxies. !nswer+ # <) 5he distinguishing feature of a starburst galaxy is !) the presence of an unusually large nu%ber of binary star syste%s containing A-ray bursters. #) a very large lu%inosity co%pared to the total lu%inosity of the Mily $ay. C) strong radio e%ission fro% ,lobes, of %aterial well outside the visible boundaries of the galaxy. &) a rate of star for%ation that %ay be 1 or %ore ti%es greater than that in the Mily $ay. !nswer+ & =) 5he unusually bright centers found in so%e galaxies are called !) active galactic nuclei. #) halos. C) super%assive blac holes. &) starbursts. !nswer+ ! 1) !ccording to current understanding' what is a quasar  !) an active galactic nucleus that is particularly bright #) a very large galaxy thought to be for%ed by the %erger of several s%aller galaxies' typically found in the center of a galaxy cluster C) any obect with an extre%ely large redshift is called a 6uasar &) a galaxy with an unusually high rate of star for%ation !nswer+ ! 11) $hich of the following pheno%ena is probably not related to the presence of a super%assive blac hole !) 6uasars #) the radio e%ission fro% radio galaxies C) the huge ets seen e%erging fro% the centers of so%e galaxies &) the large si*es of central do%inant galaxies !nswer+ & 12


12) 5he %ass of a super%assive blac hole though t to power a typical bright active galactic nucleus is roughly !)  solar %asses. #) 1 solar %asses. C) 1 trillion solar %asses. &) 1 billion solar %asses. !nswer+ & 1) !ccording to the theory that active galactic nuclei are powered by super%assive blac holes' the high lu%inosity of an active galactic nucleus pri%arily consists of !) light e%itted by hot gas in an accretion dis that swirls around the blac hole. #) intense radiation e%itted by the blac hole itself. C) the co%bined light of thousands of young' high-%ass stars that orbit the blac hole. &) radio waves e%itted fro% radio lobes found on either side of the galaxy we see in visible light. !nswer+ ! 14) !ccording to the theory that active galactic nuclei are powered by super%assive blac holes' the energy released as light co%es fro% !) nuclear fusion in the accretion dis surrounding the blac hole. #) gravitational potential energy released by %atter that is falling toward the blac hole. C) %atter-anti%atter annihilation occurring ust outside the event hori*on of the blac hole. &) ets e%erging fro% the accretion dis. !nswer+ # 19) /ntergalactic hydrogen clouds are easiest to study by looing at !) 21 c% radio e%ission. #) radio e%ission fro% %olecular hydrogen. C) A-ray e%ission. &) absorption lines in 6uasar spectra. !nswer+ & 1:) Hubble @pace 5elescope observations have shown that when the %ass of the central blac hole is very large' then !) the %ass of the halo and dis of the host galaxy is also very large. #) the host galaxy is eventually co%pletely consu%ed by the blac hole. C) the galaxy is always a spiral galaxy. &) the %ass of the bulge of the host galaxy is also very large. !nswer+ &

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1;) 5he best evidence for the existence of super%assive blac holes is !) very high orbital velocities in a very co%pact region. #) evidence for et velocities that approach the speed of light. C) large 6uantities of high-energy e%ission such as A-rays and ga%%a rays' and radio e%ission fro% relativistic electrons. &) huge dar regions in the centers of galaxies' where blac holes have been sucing in the galaxy fro% the inside out. !nswer+ ! 21.9 Mastering !strono%y Concept Qui* 1) $e can study how galaxies evolve because !) galaxies are transparent to visible light. #) we are really s%art astrono%ers. C) we can watch as they interact in real ti%e. &) the farther away we loo' the further bac in ti%e we see. !nswer+ & 2) $hich of the following state%ents is not an assu%ption used in %odels of galaxy for%ation !) 5he universe started out filled almost unifor%ly with hydrogen and heliu%. #) @o%e regions in the universe were slightly %ore dense than others. C) 5he universe is expanding. &) as contracted to for% the diss of galaxies be fore any stars were born. !nswer+ C ) "ne possible explanation for a galaxy0s type invoes the angular %o%entu% of the protogalactic cloud fro% which it for%ed. @uppose a galaxy for%s fro% a protogalactic cloud with a lot of angular %o%entu%. !ssu%ing its type has not changed due to other interactions' we0d expect this galaxy to be !) an irregular galaxy. #) an elliptical galaxy. C) a spiral galaxy. &) a torn and incoherent galaxy. !nswer+ C 4) 5wo ways in which the starting conditions in a protogalactic cloud %ight cause it to beco%e an elliptical >rather than spiral) galaxy are if the cloud begins with either !) relatively little angular %o%entu% or relatively high density. #) relatively high angular %o%entu% or relatively low density. C) relatively high %ass and a relatively low abundance of heavy ele%ents. &) relatively low %ass and a relatively high abu ndance of heavy ele%ents. !nswer+ !

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9) $hich of the following pheno%ena are not thought to be results of collisions or other interactions between galaxies !) 5he presence of very large' central do%inant galaxies in clusters of galaxies. #) 5he fact that elliptical galaxies are %ore co%%on in clusters of galaxies than outside clusters. C) @tarbursts. &) 5he fact that spiral galaxies have both dis and halo co%ponents. !nswer+ & :) /f the !ndro%eda alaxy collided with the Mily $ay' what would %ost liely happen to (arth !) 5he @un and all its planets would be crushed by collisions with stars and planets fro% the !ndro%eda alaxy. #) 3othing. C) 5he @un would not be disturbed' but the solar syste% would be ripped apa rt. &) 5he @un will turn into a red giant and explode. !nswer+ # ;) /nteractions a%ong galaxies also are thought to influence a galaxy0s type in at least so%e cases. $hich of the following does not support the idea that interactions can shape galaxies !) the fact that %ore distant galaxies have larger redshifts #) co%puter %odeling of collisions between galaxies C) the fact that galaxies with distorted appearances are %ore co%%on at great distances than nearby &) the presence of features such as ,tails, extending out of galaxies' bridges between galaxies' and rings of stars around galaxies !nswer+ ! <) $hich characteristic is not generally true of a starburst galaxy !) 5he observed features that cause us to classify it as a ,starburst, %ust be only te%porary pheno%ena in the galaxy0s history. #) /ts rate of star for%ation is %any ti%es higher than the rate of star for%ation in the Mily $ay. C) @upernovae occur so fre6uently that their effects co%bine to drive a galactic wind that blows %aterial into intergalactic space. &) 5he observed features of the starburst are thought to be caused by the presence of a super%assive blac hole in the galaxy0s center. !nswer+ & =) $hy should galaxy collisions have been %ore co%%on in the past than they are today !) alaxies were closer together in the past be cause the universe was s%aller. #) alaxies were %ore active in the past and therefore would have collided with each other %ore fre6uently. C) alaxies were %uch bigger in the past since they had not contracted co%pletely. &) alaxies attracted each other %ore strongly in the past because they were %ore %assive? they had not yet turned %ost of their %ass into stars. !nswer+ ! 15


1) ! 6uasar0s spectru% is hugely redshifted. $hat do %ost astrono%ers thin this large redshift tells us about the 6uasar !) the co%position of the 6uasar #) the distance to the 6uasar C) the si*e of the 6uasar0s central' super%assive blac hole &) the type of host galaxy in which the 6uasar resides !nswer+ # 11) ! few decades ago' there was great controversy a%ong astrono%ers over the 6uestion of 6uasar distances' with so%e arguing that 6uasars are %uch nearer than application of Hubble0s law would see% to i%ply. $hy do nearly all astrono%ers now agree that 6uasars really are 6uite far away !) $e now have i%ages and spectra that show 6uasars to be e%bedded at the centers of distant galaxies and within distant galaxy clusters. #) !ll 6uasars have large redshifts. C) 3ow that we can explain bright 6uasar e%ission with power due to the presence of super%assive blac holes' there is no reason to doubt that 6uasars are far away. &) 3o one could thin of a way to explain 6uasar speeds if they are nearby' so we concluded they %ust be far away. !nswer+ ! 12) Most active galactic nuclei are found at large distances fro% us' with relatively few nearby. $hat does this i%ply !) @uper%assive blac holes existed only when the universe was young' and no longer exist today. #) !ctive galactic nuclei can for% only at large distances fro% the Mily $ay. C) !ctive galactic nuclei exist tend to beco%e less active as they age. &) 5he ets seen in %any active galactic nuclei %ust cause the% to %ove far away fro% us. !nswer+ C 1) @uppose we observe a source of A rays that varies substantially in brightness over a period of a few days. $hat can we conclude !) 5he A-ray source is a 6uasar. #) 5he A-ray source contains a blac hole with an accretion dis. C) 5he A-ray source is no %ore than a few light-days in dia%eter. &) 5he A-ray source %ust have a strong' rapidly v arying %agnetic field. !nswer+ C

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14) !ll of the following observations are real. $hich one does not support the theory that active galactic nuclei are powered by accretion diss around %assive blac holes !) A-ray e%ission fro% active galactic nuclei can vary significantly in ti%es as short as a few days. #) 5he total lu%inosity of an active galactic nucleus can be as high as about 1 billion ti%es that of the @un. C) @pectra of active galactic nuclei show that clouds of gas are orbiting a central obect at very high speed. &) 5he %ost lu%inous active galactic nuclei have huge redshifts. !nswer+ & 19) Central blac holes can be very efficient for converting the %ass-energy of infalling %atter to ther%al energy in the accretion dis. oughly what percentage of the %ass-energy can be converted to other for%s of energy as %atter falls into a blac hole !) .;J #) 1J - 4J C) 1 - 4J &) 1J !nswer+ C 1:) 5he observed relationship between the %asses of central blac holes and the bulge %asses of galaxies i%plies that !) the blac hole will eventually suc in the rest of the galaxy. #) galaxy for%ation and super%assive blac hole for%ation %ust be related so%ehow. C) the biggest galaxies have the %ost lu%inous 6uasars. &) 6uasars were %ore co%%on 1 billion years ago than they are today. !nswer+ # 1;) Quasar spectra often show %any absorption lines that a ll appear to be due to the sa%e electron transition >such as level 1 to level 2 in hydrogen) but that fall at different wavelengths in the spectru%. $hy do we thin this is the case !) $e are seeing absorption lines fro% clouds of gas that lie be tween us and the 6uasar' and therefore each cloud has a different redshift. #) Quasars are rotating rapidly' and this rotation produces spectral lines with a wide variety of &oppler shifts. C) 5he lines fall at different wavelengths because they are produced by different che%ical ele%ents. &) 3o one nowsIit re%ains perhaps the greatest %ystery about 6uasars. !nswer+ !

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Testbank - The Cosmic Perspective

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