参考说明第13章

2TheH-RdiagramofastarclusterchangeswithStellarImagecredit:Brooks/ColeThomsonLearning34ExpansionintoaAfteralongtimeburninghydrogen,thestarcorebecomesmostlyheliumashes,surroundedbyhydrogenlayersEnergyproductionrateatthecorefallsnotenoughthermalpressuretoresistgravity5corecontractsandbecomehydrogenlayerssurroundingthecoreignitesnuclearfusionofhydrogenjustoutsidethecore,burningoutwardenergyproductionrateinouterlayersincreasestheouterlayers6thestarhasamuchlargersurfaceareabutitsdensityintheouterlayersisverylowAredgiant紅巨星alargebrightstarwithlowsurfacedensityandtemperature–ExampleBetelgeuseinOrion獵戶座內的參宿7 R~1000 8Thestarmovesright(lowertemperature)andup(brighter)intheH-Rdiagram9Thestarcorecontinuestoaccumulateheliummassofheliumcorethestar’scorecontinuestocontractbygravitationalforcetemperatureofthecorecontinuestoriseWhentemperatureofthecorereaches100millionK,nuclearreactionsofhelium(tripleprocesses)beginthreeheliumnucleifuseintoacarbonlargeincreaseinenergyproductionincoretemperaturecoreexpands;outerlayersbecomethestarmovesleft(hotter)acrosstheH-RFormassivestars,cyclesofnuclearfusionproduceheavierandheavierelementsuntilironNucleosynthesis(核合成)-originofheavyelementsintheCThestarmovesleftandrightacrosstheH-RdiagrammanyCThreemajorwaysofMassivestar→supergiant→Sun-likestar→redgiant;Core→whitedwarfReddwarf→whiteSun-likestars類太陽恆星0.4solarmass<massofthestar<4solarIntheredgiantphase,thestar’scoreishotenoughtofuseheliumintocarbon(triple-process)andthentooxygenlayersofheavyelementsuptocarbonandeCOThecoreisnothotenoughtofusecarbon,oxygenintoeCOBurningofhydrogenandheliumintheshellsreleaseslargeamountofenergythestarexpandsfurtherandlosesalargeamountofThesurfaceofagiantisheldbygravityalotofmassintheouterlayersispushedawaybystrongstellarwind(streamofhighenergyparticles)andradiationpressurePlanetarynebulae(行星狀星雲)areexpelledouterlayersofgiantstars,pushedoutbysuddenburstsofenergywhenfuelsareignited(e.g.heliumburning)Asmall,denseandhotcoreisrevealedatthenuclearreactionsextinguish,andluminositydropsSurfacetemperatureishighbutluminosityislowbecauseofitssmallsizeResidesonthelower-leftsideoftheH-Rdiagram–becomesaHotbutGasinthenebulaisionizedbyultravioletradiationfromthecentralhotstarLightisemittedwhenionsrecaptureelectrons,forminganemissionnebula Reddwarfs紅矮星<0.4solarsmall,coolandfaint,cannotformgiantsnotmassiveenough(thereforenothotenough)toburnheliumcontractslowlywhenfuelsareusedgettingsmaller,

movefromrighttoleftonH-RdiagrambecomewhiteLowmassburnshydrogenveryslowlyverylonglivesinthemainsequence(~100’sbillionyears)21Whitedwarf白矮星Sirius(天狼星) (HSTSiriusA~2solarSiriusB~1solarPropertiesofawhiteAstarinequilibrium,veryhot,small(~Earth-size),andithasaveryhighdensity(~1solarmass,1teaspoonofmatter~15tons)–SiriusBB星~1solarmass,0.76Earthsradius,surfacetemperature~32,500K,density~3106g/ccThegravityisresistedbyelectrondegeneracypressure電子簡併壓力whichispredictedbyquantummechanics(量子力學).2atlevel1,8atlevel2,WhynotallatlevelNotbecauseofrepulsionbetweenButdegeneracyExplainedbyquantumElectrondegeneracypressure:Whendensityisveryhigh,electronsarepressedtogether.Butquantummechanicspredictsthatelectronsdonotliketobesqueezedtogether;theyexertstrongoutwardpressuretoresist.Stronggravityonitssurface(~105 thatofEarth’s)Awhitedwarfradiatesenergybecomescoldanddarkafterbillionsofbecomesablackdwarf(黑矮星endswithaquiet::Apersonjustdied,bodystillwarm

AcoldcorpseItIttakestoolongforawhitedwarftocooldown.Thereforedwarfdoesnotexist(yet)inourChandrasekharlimit(陳德拉極限Themaximummassofawhitedwarfthattheelectrondegeneracypressurecansupport(1.4solarmasses).Thedegeneracypressurecannolongerresistgravitybeyondthislimit,i.e.,thestarwillfurtherMassofthestar>4solarcontinueburningofheavierandheavierelementsiron-themosttightlyboundedBindingenergycannotproduceanymoreenergybyfusinganinertironcoreisformedinwhichnoenergyisthestarcorecannotresistthecontractingforceofcollapses Notevenelectrondegeneracypressurecanstopthecorecontractsfasteranddensitygoeshigherandhigher.Whendensity~1014gcm-3,nucleons(neutronsandprotons)arepressedtogether,exertingstrongpressuretoresist,reactinglikeahardcore. innercorerebounds,buildinguppowerfulshockwaveswhichpropagateoutward,triggeringnuclearreactionsintheouterlayers.AnextremelyhighenergyexplosionresultsCompletedestructionofthestar’souterlayersinaveryshorttimeCrabNebula(蟹狀星雲)M1istheremnantofthesupernovain1054. Asmall,extremelydensecoreofneutronmattermayremainaftertheexplosionNeutronstar中子星Formoremassivestars(M>~25Msun)BlackExampleofSupernova1987A(~51kpcfrom(10daysafterexplosion)(beforeRingofgas(expelled~20000yrsbeforetheHSTimages(1994–2006)

Glowingofthering(duetotheheatingoftheoutgoingshockwave) Supernovaclassification(fromtheExplosivenuclearburningofawhitedwarf(duetotheaccretionoffromacompanioninabinary

TypeIb,Ic,IICollapseofmassivestars(aswehavediscussed)NeutronStar中子星Ifthemassofthecoreofadyingstaris>~1.4GravitywinsoverelectrondegeneracystellarcorecontinuestodensitygoesAtdensity~1012g/cm3 :thefollowingreactioncanoccurproton+electron→neutron+neutrinosmatterbecomesneutronIfthe