英语听力英语高级听力材料Supermassive Black Holes.docx

英语听力英语高级听力材料Supermassive Black Holes.docx

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英语听力英语高级听力材料SupermassiveBlackHoles

InMarch2000,twoastronomersmadeanextraordinarydiscovery,onethatissettooverturnourunderstandingofhowtheuniverseformed.

We'renevergoingtoseeatimelikethisinastronomyagain.

Really,theairisfilledwithnewdiscoveriesandnewideas.

Whattheydiscoveredwasaverysimplerelationship,arelationshipbetweenthegalaxyweliveinandthemostdestructiveforceintheuniverse,asupermassiveblackhole.Itsettheworldofcosmologyalight.

Peoplewerenotthatexcitedaboutsupermassiveblackholes.Thegeneralastronomerdidnotcarethatmuchaboutsupermassiveblackholes.Nowtheyhavetoand,nowthey'dbetter.

Theultimateaimofcosmologyistounderstandhowtheuniversewasformed.Oneofthemostimportantquestionsishowgalaxieswerecreated,becausewithoutthemwewouldn'texist.

Galaxiescontainalmostallofthestarsweseeintheuniverseand,maybetheplaceswhereallstarsintheuniversewillbecreated.Andstarsarewhatproduceoxygen,carbon,planets,everythingyouneedforlife.Andwithoutlifeyoudon'tgetastronomers.

Weseeourgalaxy,theMilkyWay,asabandofstarsinthesky.Infact,itisagiantrotatingdisc,200,000lightyearswide.Itcontainsover200billionstarslikeourownsun,circlingslowlyaroundthecenter.

Butwearejustonein125billiongalaxiesofdifferentshapesandsizesspinningthroughspace.Yetscientistshaven'tbeenabletoexplainhowasingleoneofthesegalaxieswascreated.

Galaxyformationisaverycomplicatedprocess,wethink,itinvolvesgravityanditinvolveslargeballsofgascolliding,itinvolvesthedynamicsofstarsanditinvolvesthechemistryofthegascomingtogether.

Allweknowisthatwhentheuniversewasyoung,therewerenostarsorplanets,justgreatswirlingcloudsofhydrogengas.Themysteryishoweachofthesecloudsturnedintothecomplexgalaxiesofstarsweseetoday.

Wejustdon'tknowhowtheydoit,howgalaxiesformedoutofthe,theionizedhotgasthat（'s）filledtheuniverseisstillphysicsthatwedonotreallyunderstandyet.

Exactlyhowgalaxieswerecreatedhastroubledtheworld'sleadingastronomersandphysicistsfordecades.ButinMarch2000,scientistsfoundevidenceforanextraordinaryanswer.

TheNukerteamisagroupofworldrespectedastronomers,buttheyarenotgalaxyexperts.Theyareexpertsinthemostviolentanddestructiveforcesknowntoscience---supermassiveblackholes.Untilrecently,supermassiveblackholesweremeretheory.Thesearegiantblackholesofapocalypticproportion.

Supermassiveblackholesareamilliontoabilliontimesthemassof,ofa,ofatypicalblackhole.

Theycouldfillawholesolarsystem.

Asupermassiveblackholeisquitesimplygravitygonemad.Anobjectofsuchconcentratedmatteritsgravitationalpullisinsatiable.Nothingcanescapeit,notevenlightitself.Anythingthatgetsclose-gas,starsandentiresolarsystemsaresuckedintooblivion.Itevendestroystheveryfabricoftheuniverse.Ifyouthinkoftheuniverseasaspace-timeweb,thegravityofordinarystarsandplanetscreatesadentinthisweb.Buttheimmensegravityofasupermassiveblackholeissodestructivethatitdistortsspacetimetobreakingpoint.

Attheheartofasupermassiveblackholeisoneofthemostmysteriousthingsinphysics-thesingularity（奇点）,apointwherespace,timeandallknownlawsofphysicsfallapart.

Whathappensatthecenterofthesingularityisacompletemystery.Andsolvingitisgoingtorequirenewphysicsthatwejustdon'thaverightnow.Somepeoplethinkyoucanfallthroughthesingularityandpopoutinanotherpartoftheuniverse.Thetheoriesforthesingularityare,someofthemarevery,veryradical.Wejustdon'tknow.

Supermassiveblackholesaresobizarrethatuntilrecentlymanyscientistsdoubtedtheyexistedatall.Theywereanextremeideadreamtuptoexplainaveryrareanddistanttypeofgalaxy:

activegalaxies.Theseareamongstthebrightestobjectsintheuniverse.Thesegalaxieshaveabrilliantburningcorewithvastjetsofenergyspurtingoutofthecenter.

oblivion:

destruction,extinction

space-time:

thefour-dimensionalcontinuuminwhichallobjectsarelocatedandalleventsoccur,viewedasasingleandcontinuousframeworkforexistence.Space-timeconsistsoflength,width,depth,andtime.

singularity:

Astrophysics.Apointinspace-timeatwhichgravitationalforcescausemattertohaveinfinitedensityandinfinitesimalvolume,andspaceandtimetobecomeinfinitelydistorted

anactivegalaxyisagalaxywhereasignificantfractionoftheenergyoutputisnotemittedbythenormalcomponentsofagalaxy:

stars,dustandinterstellargas.Thisenergy,dependingontheactivegalaxytype,canbeemittedacrossmostoftheelectromagneticspectrum,asinfrared,radiowaves,UltraViolet,X-rayandgammarays.

Thisferociousheartofbrillianthotgasiscalledaquasar.Scientiststhoughtthiswhirlingmassmightbecausedbyagiantblackholesuckingupgasandstars,literallyfeedingonthecenterofagalaxy.

Theideaisthatthequasarsthatweseethatlooksobrightarenottheblackhole,thesupermassiveblackhole.Theyarethegasthat'sjustabouttofallintothesupermassiveblackhole,that'sgoingaroundit,shiningverybrightlyjustbeforeitdisappearsdownintotheblackhole.

Agiantblackholewouldhaveagravitationalpullsooverwhelming,itwouldhurlgasandstarsarounditatalmostthespeedoflight.Theviolentclashingwouldheatthegasuptooveramilliondegrees.

Thegasrubsagainstitselfessentiallyandgetsextremelyhot,andextremelyhotgasshinesverybrightly.

Inreality,althoughaquasarburnsbrightly,itisactuallyimpossibletoseeifthere'sablackholeinthemiddle.Paradoxically,theblackholeismadeinvisiblebythefactthatitswallowslight.Soforyears,noonecouldbecertainifsupermassiveblackholesreallydidexistattheheartofthesestrangeactivegalaxies.TheNukershavespentthelasttwodecadeshuntingfortheseelusivemonsters.Thefirstproblemtheyfacedwastoprovethatsupermassiveblackholesexistedatall.Whattheyweretodiscoverwouldbestrangerthanmostpeoplecouldhaveimagined.OneofthefirstoftheNukerstotrytofindonewasAlanDressler.In1983hecametothePalomarTelescopeinCaliforniaconvincedthathe'dfoundawaytoprovethatsupermassiveblackholesexist.

Youcan'tseeablackholedirectly.That'swhatmakesitablackhole.Sowhatyouarelookingforisevidenceofitsgravity.Youareeverlookingathowitpullsonthestarsthatarecomingnearby.

Dresslerknewthatalthoughablackholeisinvisible,itsimmensegravitywouldhurlstarsarounditatover500,000kilometersanhour.

quasar:

类星体Astronomyamassiveandextremelyremotecelestialobjectwhichemitslargeamountsofenergyandtypicallyshowsastarlikeimage

Bymeasuringhowfastthesestarsweremoving,hecouldproveiftherereallywasablackholeatthecenterofanactivegalaxy.

IpickedagalaxynearbywhichiscalledNGC1068,anactivegalaxy,whichmeantthatitprobablyhadasupermassiveblackholeinit,atleast,that'swhatwewantedtoprove.

TobecertainthatthestarsweremovingunnaturallyfastinNGC1068,Dresslarwantedtocomparethemwithstarsinanormalgalaxywithoutablackhole.Starscirclingaroundaweakcenterofgravitywouldmoveathalfthespeed.Soforthiscomparison,hechosetheveryordinarygalaxynextdoortous,Andromeda（仙女座）,withaquiet,inactivecenterlikeourown.

Tomeasurethespeedofthestarsinthesetwoverydifferentgalaxies,Dresslarusedaninstrumentcalledaspectroscope.Thislooksatthechangingpatternoflightcomingfromstarsastheyrotatearoundthegalaxycore.Thespectroscopeshowsthecenterofthegalaxyasawhitebandandthemovementofstarsaroundthecoreistracedbyadark,verticalline.Ifthestarsofthegalaxy'scenterarecirclingslowly,thenthedarkbandwouldshowhardlyanychange,butiftheyaretravelingatgreatspeed,whizzingtowardsandawayfromuseithersideofasupermassiveblackhole,thenthedarkbandshouldshowasuddenshiftacrossthecenterofthegalaxy.

Iwouldexpecttoseesomeratherrapidchangeinthisdarklinesothatthere'dbeaverybigchangeinthespeedfromonesideofthegalaxytotheother,verysuddenly,rightoverthecenterandthatwouldshowthatthestarsweremovingveryrapidlyinthecenterofthegalaxybecauseoftheinfluenceofthegreatmassinthecenter,thesupermassiveblackhole.

Overthenextafewnights,DresslarmeasuredthespeedofthestarsinNGC1068andinAndromeda.

spectroscope:

anapparatusforproducingandrecordingspectraforexamination

whiz:

movequicklythroughtheairwithawhistlingorwhooshingsound

Whentheresultscamedownfromthetelescopehesawsomethingthatwascompletelyunexpected.Thepicturefromtheactivegalaxywherehehopedtofindablackholewasunreadable.NGC1068wasjusttoofarawayforthetelescopetogetaclearpicture.ThesurprisecamefromAndromeda,thequiet,normalgalaxyrightnexttous.

IwasastonishedwhenIfoundwhatIwaslookingfor,butnotwhereIwaslookingforit.Thisjoginthisdarkbandshowsthatononesidethestarsaremovingveryrapidlyawayfromusat150kilometersasecondwhichis500,000kilometersanhour.

Dresslerthoughttherecouldonlybeonethingthatwouldcausethestarstomovethisfast:

asupermassiveblackholeandhewasn'talone.FellowNukerJohnKormendyhadfoundexactlythesamething.

ThemomentIcouldseethatwiggle,soIknewessentiallyinstantlythattherewasaverygoodchancethiswouldbeasupermassive