很全面的资料-中子星与黑洞 Neutron Stars and Black Holes

NeutronStarsandBlackHolesTheprecedingchaptershavetracedthestoryofstarsfromtheirbirthascloudsofgasintheinterstellarmediumtotheirfinalcollapse.Thischapterfinishesthestorybydiscussingthekindsofobjectsthatremainafteramassivestardies.Howstrangeandwonderfulthatwehumanscantalkaboutplacesintheuniversewheregravityissostrongitbendsspace,slowstime,andcurveslightbackonitself!Tocarryonthesediscussions,astronomershavelearnedtousethelanguageofrelativity.Throughoutthischapter,rememberthatourgeneralizeddiscussionsaremadepossiblebyastronomersstudyinggeneralrelativityinallitsmathematicalsophistication.Thatis,ourunderstandingrestsonarichfoundationoftheory.Thischapterendsthestoryofindividualstars.Thenextthreechapters,however,extendthatstorytoincludethegiantcommunitiesinwhichstarslive—thegalaxies.GuidepostI.NeutronStarsA.TheoreticalPredictionofNeutronStarsB.TheDiscoveryofPulsarsC.AModelPulsarD.TheEvolutionofPulsarsE.BinaryPulsarsF.TheFastestPulsarsG.PulsarPlanetsII.BlackHolesA.EscapeVelocityB.SchwarzschildBlackHolesC.BlackHolesHaveNoHairD.ALeapintoaBlackHoleE.TheSearchforBlackHolesOutlineIII.CompactObjectswithDisksandJetsA.X-RayBurstersB.AccretionDiskObservationsC.JetsofEnergyfromCompactObjectsD.Gamma-RayBurstsOutline(continued)NeutronStarsThecentralcorewillcollapseintoacompactobjectof~afewMsun.AsupernovaexplosionofaM8Msunstarblowsawayitsouterlayers.FormationofNeutronStarsCompactobjectsmoremassivethantheChandrasekharLimit(1.4Msun)collapsefurther.Pressurebecomessohighthatelectronsandprotonscombinetoformstableneutronsthroughouttheobject:p+e-n+neNeutronStarPropertiesofNeutronStarsTypicalsize:R~10kmMass:M~1.4–3MsunDensity:r~1014g/cm3Pieceofneutronstarmatterofthesizeofasugarcubehasamassof~100milliontons!!!DiscoveryofPulsars=Collapsingstellarcorespinsuptoperiodsof~afewmilliseconds.Angularmomentumconservation=Rapidlypulsed(opticalandradio)emissionfromsomeobjectsinterpretedasspinperiodofneutronstarsMagneticfieldsareamplifieduptoB~109–1015G.(upto1012timestheaveragemagneticfieldofthesun)Pulsars/NeutronStarsWien’sdisplacementlaw,lmax=3,000,000nm/T[K]givesamaximumwavelengthoflmax=3nm,whichcorrespondstoX-rays.CasAinX-raysNeutronstarsurfacehasatemperatureof~1millionK.PulsarPeriodsOvertime,pulsarsloseenergyandangularmomentum=Pulsarrotationisgraduallyslowingdown.LighthouseModelofPulsarsAPulsar’smagneticfieldhasadipolestructure,justlikeEarth.Radiationisemittedmostlyalongthemagneticpoles.NeutronStar(SLIDESHOWMODEONLY)ImagesofPulsarsandOtherNeutronStarsThevelaPulsarmovingthroughinterstellarspaceTheCrabnebulaandpulsarTheCrabPulsarRemnantofasupernovaobservedinA.D.1054Pulsarwind+jetsTheCrabPulsar(2)VisualimageX-rayimageLightCurvesoftheCrabPulsarProperMotionofNeutronStarsSomeneutronstarsaremovingrapidlythroughinterstellarspace.ThismightbearesultofanisotropiesduringthesupernovaexplosionformingtheneutronstarBinaryPulsarsSomepulsarsformbinarieswithotherneutronstars(orblackholes).RadialvelocitiesresultingfromtheorbitalmotionlengthenthepulsarperiodwhenthepulsarismovingawayfromEarth...…andshortenthepulsarperiodwhenitisapproachingEarth.NeutronStarsinBinarySystems:X-rayBinariesExample:HerX-12Msun(F-type)starNeutronstarAccretiondiskmaterialheatstoseveralmillionK=X-rayemissionStareclipsesneutronstarandaccretiondiskperiodicallyOrbitalperiod=1.7daysPulsarPlanetsSomepulsarshaveplanetsorbitingaroundthem.Justlikeinbinarypulsars,thiscanbediscoveredthroughvariationsofthepulsarperiod.Astheplanetsorbitaroundthepulsar,theycauseittowobblearound,resultinginslightchangesoftheobservedpulsarperiod.BlackHolesJustlikewhitedwarfs(Chandrasekharlimit:1.4Msun),thereisamasslimitforneutronstars:Neutronstarscannotexistwithmasses3MsunWeknowofnomechanismtohaltthecollapseofacompactobjectwith3Msun.Itwillcollapseintoasinglepoint–asingularity:=ABlackHole!EscapeVelocityVelocityneededtoescapeEarth’sgravityfromthesurface:vesc≈11.6km/s.vescNow,gravitationalforcedecreaseswithdistance(~1/d2)=Startingouthighabovethesurface=lowerescapevelocity.vescvescIfyoucouldcompressEarthtoasmallerradius=higherescapevelocityfromthesurface.TheSchwarzschildRadius=Thereisalimitingradiuswheretheescapevelocityreachesthespeedoflight,c:Vesc=cRs=2GM____c2RsiscalledtheSchwarzschildRadius.G=Universalconst.ofgravityM=MassSchwarzschildRadiusandEventHorizonNoobjectcantravelfasterthanthespeedoflightWehavenowayoffindingoutwhat’shappeninginsidetheSchwarzschildradius.=nothing(notevenlight)canescapefrominsidetheSchwarzschildradius“Eventhorizon”SchwarzschildRadiusofBlackHole(SLIDESHOWMODEONLY)BlackHolesinSupernovaRemnantsSomesupernovaremnantswithnopulsar/neutronstarinthecentermaycontainblackholes.SchwarzschildRadii“BlackHolesHaveNoHair”Matterformingablackholeislosingalmostallofitsproperties.BlackHolesarecompletelydeterminedby3quantities:MassAngularMomentum(ElectricCharge)GeneralRelativityEffectsNearBlackHolesAnastronautdescendingdowntowardstheeventhorizonoftheBHwillbestretchedvertically(tidaleffects)andsqueezedlaterally.GeneralRelativityEffectsNearBlackHoles(2)TimedilationEventHorizonClocksstartingat12:00ateachp