专业英语Astrophysics培训课件

Astrophysics&CosmologyNowweleaptothelargest–starsandgalaxies.Thesetwoextremerealms,elementaryparticlesandthecosmos,areamongthemostintriguing(引起兴趣的)andexcitingsubjectsinscience.

Useofthetechniquesandideasofphysicstostudytheheavensisoftenreferredtoasastrophysics.AtthebaseofourpresenttheoreticalunderstandingoftheuniverseisEinstein’sgeneraltheoryofrelativityanditstheoryofgravitation–stars星体galaxy[‘glksi]星系,银河cosmos[‘k

zm

s]宇宙astrophysics[str

’fIzIks]

天体物理学generaltheoryofrelativity广义相对论专业英语PhysicsEnglishforinthelarge-scalestructureoftheuniverse,gravityisthedominantforce.Generalrelativityservesalsoasthefoundationformoderncosmology,whichisthestudyoftheuniverseasawhole.Cosmologydealsespeciallywiththesearchforatheoreticalframeworktounderstandtheobserveduniverse,itsorigin,anditsfuture.cosmology[k

z’m

l

d

i]

宇宙学专业英语PhysicsEnglishplanet行星telescopic[telis’k

pik]用望远镜看的1

StarsandGalaxiesAccordingtotheancients,thestars,exceptforthefewthatseemedtomove(theplanets),werefixedonasphere.Theuniversewasneatlyself-contained,andweonEarthwereatornearitscenter.ButinthecenturiesfollowingGalileo’sfirsttelescopicobservationsoftheheavensin1610,ourviewoftheuniversehaschangeddramatically.专业英语PhysicsEnglishWenolongerplaceourselvesatthecenter,andweviewtheuniverseasvastlylarger.Thedistancesinvolvedaresogreatthatwespecifythemintermsofthedistancetraveled(inavacuum)bylightinoneyear:1light-year(ly)=9.47×1015m.Besideslight-year,inastrophysics,thefollowingdistanceunitsareoftenused:Astronomicalunit(AU)

ThisisthemeanradiusoftheEarth’sorbitaroundtheSun.1AU=1.50×1011m.light-year光年astronomical[

str

’n

mIk(

)l]unit(AU)天文单位专业英语PhysicsEnglishTheEarthisoneofmanyplanets

inorbitaroundtheSun.TheSun,planets,andotherobjectsinorbitaretogetherknownastheSolarSystem.Mostoftheplanetsmoveinnear-circularorbits.Manyhavesmallermoonsorbitingthem.Cometsaresmall,icyobjectsinhighlyellipticalorbitsaroundtheSun.Planets,moons,andcometsareonlyvisiblebecausetheyreflecttheSun’slight.SolarSystem太阳系moon卫星comet彗星专业英语PhysicsEnglishOnaclearmoonlessnight,thousandsofstarsofvaryingdegreesofbrightnesscanbeseen,aswellastheelongated(伸长的)cloudystripe(条纹)knownastheMilkyWay.ItwasGalileowhofirstobserved,about1610,thattheMilkyWayiscomprisedofcountlessindividualstars.AsectionoftheMilkyWayMilkyWay银河Acenturyandahalflater,ThomasWrightsuggestedthattheMilkyWaywasaflatdiscofstarsextendingtogreatdistancesinaplane,whichwecalltheGalaxy(Greekfor“milkyway”).OurGalaxyhasadiameterofalmost100,000light-yearsandathicknessofveryroughly2000light-years.Ithasabulging(凸出)centralnucleusandspiralarms.ThetotalmassofallthestarsinourGalaxyisabout3

1041kg.OurSun,whichseemstobejustanotherstar,islocatedmorethanhalfwayfromthecentertotheedge,about28,000lysfromthecenter.OurGalaxycontainsabout1011stars.Thesunorbitsthegalactic[g

‘l

ktik]centerapproximatelyonceevery200millionyears,soitsspeedisabout250km/srelativetothecenteroftheGalaxy.专业英语PhysicsEnglish100,000lysOurSunendviewintheplaneofthedisctopview,lookingdownonthedisc2000lys牛郎Altair[

l’t

]天鹰座

织女Vega[‘vi:g

]天琴座专业英语PhysicsEnglishWecanseestarsbothwithinandoutsidetheMilkyWaybytelescope,manyfaintcloudypatches（斑点）intheskywhichwereallreferredtoonceas“nebula”(Latinfor“clouds”).Afewofthese,suchasthoseintheconstellationsAndromedaandOrion,canactuallybediscernedwiththenakedeyeonaclearnight.ThisglobularstarclusterislocatedintheconstellationHercules[‘h

:kjuli:z](武仙座).nebula星云Constellation[knst’lei

n]星座Andromeda[

n’dr

mid

]仙女座Orion[

‘rai

n]猎户座专业英语PhysicsEnglishOthersareglowingcloudsofgasordust,anditisforthesethatwenowmainlyreservethewordnebula.Mostfascinatingarethosethatbelongtoathirdcategory:theyoftenhavefairlyregularellipticalshapesandseemtobeagreatdistancebeyondourGalaxy.Theyappearellipticalbecauseweseethematanangle,andarefaintbecausetheyaresodistant.Atfirstitwasnotuniversallyacceptedthattheseobjectswereextragalactic–thatis,outsideourGalaxy.Theverylargetelescopesconstructedinthiscenturyrevealedthatindividualstarscouldberesolvedwithintheseextragalacticobjectsandthatmanycontainedspiralarms.extragalactic[,ekstr

g

‘l

ktik]银河系外的,天河外的专业英语SpiralgalaxyintheconstellationHydra长蛇座TheWhirlpoolgalaxyThegaseousnebula专业英语PhysicsEnglishEdwinHubble(1889-1953),whodidmuchofthisobservationalworkinthe1920susingthetelescope,wasalsoabletodemonstratethattheseobjectswereindeedextragalacticbecauseoftheirgreatdistances.Thesenebulaaregalaxiessimilartoours.Today,thelargesttelescopescanseeabout1011galaxies.Galaxiestendtobegroupedingalaxy

clusters,withanywherefromafewtomanythousandsofgalaxiesineachcluster.Furthermore,clustersthemselvesseemtobeorganizedintoevenlargeraggregates(集合体):clustersofclustersofgalaxies,orsuperclusters.Thegalaxiesnearestusareabout2millionlight-yearsaway.supercluster超星系团专业英语PhysicsEnglishBesidestheusualstars,clustersofstars,galaxies,andclustersandsuperclustersofgalaxies,theuniversecontainsanumberofotherinterestingobjects.Amongthesearestarsknownasredgiants,whitedwarfs,neutronstars,blackholesandsoon.redgiant红巨星whitedwarf白矮星neutronstar中子星blackhole黑洞专业英语PhysicsEnglish2BirthofastarStarsforminhugecloudsofgas(mainlyhydrogen)anddustcallednebulae(星云).Thesunformedinanebulaabout5109yearsago.Theprocesstookabout5107years.Gravitypulledmoreandmorenebularmatterintoaconcentratedclumpcalledaprotostar(原始星体).ThelossofGravitycausedariseincoretemperaturewhichtriggeredthefusion(聚变)ofhydrogenandthereleaseofenergy.Thermalactivitystoppedfurthergravitationalcollapse(引力坍缩).Thesunhadbecomeamainsequence（主星序）star.专业英语PhysicsEnglish3LifeanddeathofastarThesungetsmostofitsenergyfromtheproton-protonchain(质子—质子链),amulti-stagefusionprocesswhichconvertshydrogen-1intohelium-4.Hotter,moremassivestarsusetheCNOcycle.Thisalsochangeshydrogen-1intohelium-4,butinvolvescarbon,nitrogen(氮),andoxygennuclei.TheSunisabouthalfwaythroughitslifeonthemainsequence(about1010year).Hotter,moremassivestarsconsumehydrogenmorequicklyandhaveshortermainsequencelives.专业英语PhysicsEnglishWhenallitshydrogenhasbeenconvertedintohelium,theSunwilltakethepathshownontheH-Rdiagrambelow.1231.Thecorecollapses.Thesunbecomesaredgiant(红巨星)asitsouterlayersexpandandcool(andengulf(吞没)theEarth).Withthecoretemperaturerisingtoover108K,energyisreleasedbythefusionofheliumintocarbon.专业英语PhysicsEnglish专业英语PhysicsEnglish2.Afterfurtherchanges,theouterlayersexpandanddriftoffintospace.Thecoreandinnerlayers123becomeawhitedwarf(白矮星)whosecoreissodensethatthenormalatomicstructurebreaksdown.Theelectronsformadegenerateelectrongas(派生电子气体)whosepressurestopsfurthercollapse.3.Fusioncease.Thewhitedwarfcoolsandfadesforever.专业英语PhysicsEnglishNote:StarslessmassivethantheSunendupaswhitedwarfs,withoutgoingthroughthegiantstages.Massivestarsbecomegiantsorsupergiants,thenendupasneutronstars

or

blackholes.supergiantstar超巨星neutronstar中子星blackhole黑洞专业英语PhysicsEnglish4MorestellarobjectsSupernova(超新星)

Whenamassivestarentersitsgiantphase,itscorebecomessohotthatcarbonisfusedintoheavierelements.Ifthestarexceedsabout8solar(Sun’s)masses,ironisproduced.Asthisisatthetopofthebindingenergy(结合能)curve,fusionnolongersuppliesenergy.Thecorecollapses,causingashockwave(冲击波)whichblowsawaythestar’souterlayersinahugeexplosioncalledasupernova[,sju:p

’n

uv

].Forafewdays,asupernovaismillionsoftimesbrighterthanastar.Elementsejectedfromasupernova

eventually“seed”thenebulae(星云)inwhichnewstars(恒星)andplanets(行星)willform.专业英语PhysicsEnglishNeutronstars(中子星)

Ifthecoreofasupernova(超新星)exceedsabout1.4solarmasses,thedegenerateelectrongas(派生电子气体)cannotresistgravitationalcollapse(引力坍缩).Electronsandprotonsarepushedtogethertoformneutrons.Theresultisaneutronstar--essentiallyagiantnucleusabout10-30kmacross.Pulsars[‘pls:](脉冲星)Theseemitradio,light,orX-raypulsesatupto500timespersecond.Theyarebelievedtoberapidlyspinningneutronstars.Pulsarsaredetectedbecausethestarsendsouttwonarrowradiationbeamswhichrotatewithit,ratherlikethebeamsoflightfromalighthouse(灯塔).专业英语PhysicsEnglishPulsarsneutronstarmagneticaxisradiationspinaxisThisshowshowradiopulsarsradiatetheirradiowaves

专业英语PhysicsEnglishBlackholesIfthecoreofasupernovaexceedsabout2.5solarmasses,eventheneutronsformedcannotresistgravitationalcollapse.Thecoreshrinks(收缩)tobecomeablackholefromwhichnoparticlesorradiationcanescape.thegalaxyNGC4261theblackhole专业英语PhysicsEnglishBinarystars

(双子星)Thesearetwostarswhichrotateaboutacommoncenterofmass.Iftheyareclose,gravitymaypullmaterialfromonetotheother.Ifoneisaneutronstarorblackhole,materialfallingintoitwillgiveoffX-rays.Quasars

(类星体)ThesehaveredshiftswhichsuggestthattheyarethemostdistantobjectsintheUniverse.Iftheyreallyaredistant,theyradiateasmuchenergyassomegalaxies,buthaveonlythevolumeofasolarsystem.Eachmaybetheactivecenterofagalaxywherenebularmattersurroundsasupermassive(特大质量的)blackhole.vvoidgalaxies5ThestructureoftheUniverseThestudyoftheUniverse,itsorigins,andevolutioniscalledcosmology(宇宙学).TheUniversecontainsbillionsofgalaxies.Theiraverageseparationis~106light-years.Together,theyformanetworkoflong,clumpy(丛,簇)

filaments(细丝)withhuge

voidsspaces

inbetween.Despitetheirlocal

irregularities,thegalaxiesare,ona

largescale,evenly(均匀地)distributed

inalldirections.Themotionofgalaxies

indicatesthattheyaresurroundedby

massiveamountofthinly-spread,

invisiblematerial.Thisiscalleddarkmatter

(暗物质).

Itsnatureisnotyetknown.专业英语PhysicsEnglish6Hubble’slaw(哈勃定律)MeasurementsofDopplerredshiftsindicatethat,ingeneral,thegalaxiesarereceding(后退)fromeachother.Thefurtherawaythegalaxy,thegreaterisitsredshiftand,therefore,thegreateritsrecessionvelocity.AccordingtoHubble’slaw,thedistancedofagalaxyanditsrecessionvelocity[vi’l

siti]varelinkedbythisequation:400800120002468approximatedistance/Mpcrecessionvelocity/104kms-1(2)专业英语PhysicsEnglishH0iscalledtheHubbleconstant.Largedistancesaredifficulttoestimateaccurately,sothevalueofH0hasahighuncertainty.However,itisthoughttolieintherange50-100kms-1Mpc-1.Itsvalueisimportantforseveralreasons:Itenablesthedistancesofthemostremotegalaxiestobe

estimatedfromtheirredshifts.TheageoftheUniversecanbeestimatedfromit(H0hasdimensionsof1/time).ThefateoftheUniversedependsonit.专业英语PhysicsEnglish7TheexpandingUniverseThemostgenerallyacceptedexplanationofgalacticredshiftsisthattheUniverseisexpanding.Atzerotime,allitsmatterandenergywastogetherinahighlyconcentratedstate.EstimatingtheageoftheUniverseIfagalaxyisdfromourown,andhasasteadyrecessionvelocity

v,thenseparationofthegalaxiesmusthaveoccurredatatimed/vago.ThisrepresentstheapproximateageoftheUniverse.Fromequation(2)d/v=1/H0,so:TheageoftheUniverse1/H0专业英语PhysicsEnglishThisgivesanageintherange1-2

1010years(10-20billionyears).Note:Theabovecalculationassumesconstantv.Inreality,visthoughttohaveincreasedwithtime.Thisgivesareducedageestimate.Olber’sparadox(奥伯斯佯谬)

Inthe17thcentury,itwaspointedoutthat,ifthestarscontinuedouttoinfinity,thenightskyshouldbewhite,notdark–becauselightmustbecomingfromeverypossibledirectioninthesky.Thisbecameknownas

Olber’sparadox[‘prdks].Tworeasonsforthedarknightskyhavebeensuggested:InanexpandingUniverse,red-shiftedwavelengthsmeanreducedphotonenergies(光子能),sotheintensityofthelightfromdistantstarsisreduced.ThereisalimittoourobservableUniverse.If,say,theUniverseis15billionyearsold,thenwehaveyettoreceivelightfromstarsmorethan15billionlight-yearsaway.Soeverythingbeyondthatdistancelooksdark.Thecosmologicalprinciple(宇宙学原理)

Thissaysthat,apartfromsmall-scaleirregularities,theUniverseshouldappearthesamefromallpointswithinit(i.e.thedistributionofgalaxiesandtheirrecessionvelocitiesshouldappearthesamefromallpoints).专业英语PhysicsEnglish8Thehotbigbangtheory(热大爆炸理论)Accordingtothistheory,sometimescalledthestandardmodel,theUniverse(andtime)beganabout10-20billionyearsagowhenasingle,hot“superatom”eruptedinaburstofenergycalledthebigbang(宇宙大爆炸).Asexpansionandcoolingtookplace,particlesandantiparticlesformed.Furthercoolingmeantthatcombinationswerepossible,sonucleiandthenatomsformed–andeventuallygalaxies.专业英语PhysicsEnglishFundamentalforcesIntheinstantafterthebigbang,thefundamentalforcesexistedasonesuperforce(超力).Butwithin10-11s,theyhadseparatedfromeachother.Cosmicbackground(宇宙本底)Thereisasteadybackgroundradiation(背景辐射,本底辐射)whichcomesfromeverydirectioninspace.Itpeaksinthemicrowaveregion,andcorrespondstotheradiationfromablackbodyat2.7K.Itisthoughttobethered-shiftedremnant(残迹)ofradiationfromthebigbang.Itspresenceispredictedbythebigbangtheory.专业英语PhysicsEnglishInflation(膨胀)Thestandardmodelcannotsatisfactorilyexplainwhy,onalargescale,theUniverseanditsmicrowavebackgroundradiationaresouniform.Mathematically,itispossibletoovercomethisdifficultybyassumingthattheearlyUniversewentthroughabriefperiodofveryrapidinflation(胀大),whenitsvolumeincreasedbyafactor1050.9ThefateoftheUniverseGravityisslowingtheexpansionoftheUniverse.ThefateoftheUniversedependsonhowitsaveragedensitycompareswithacertaincriticaldensity(临界密度):Iftheexpansionreachesamaximum,andi