Most Population III Supernovae are Duds

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arXiv:0808.3282v1 [astro-ph] 25 Aug 2008MOSTPOPULATIONIIISUPERNOVAEAREDUDSRobertL.KuruczHarvard-SmithsonianCenterforAstrophysics

August22,2008

0MOSTPOPULATIONIIISUPERNOVAEAREDUDSRobertL.KuruczHarvard-SmithsonianCenterforAstrophysics60GardenSt,Cambridge,MA02138

AbstractOnePopulationIIIdudsupernovaproducesenoughoxygentoenable107solarmassesofprimordialgastobindintoMdwarfs.ThisispossiblebecauseradiationfromotherPopulationIIIstarsimplodesthemixtureofoxygenejectaandprimordialgasintoaglobularcluster.Modelatmospherecalculationsforoxygendwarfsshowthatwaterblocksmostoftheinfraredflux.Thefluxisredistributedintothevisibletoproduceanunfamiliar,distinctiveenergydistribution.Onemilliondudsupernovaeinalargeprotogalaxyaresufficienttoproducethe“darkmatter”halo.

Subjectheadings:supernovae—darkmatter

IntroductionMostofthephysicsandliteratureonPopulationIIIstarformationandonPopulationIIIsupernovaearespeculative,asisthispaper.Thegoalofsupernovamodellingisalwaystoproducesupernovaexplosionsandproducts.Methodsandphysicsthatdonotworktoproduceanexplosiononthecomputerarenotinteresting,arenotfunded,anddonotproducejobs.Howcanweeverdiscoverhowtomakeduds,orthatdudsevenexist?HereImakepredictionsaboutdudsupernovaeandabout“darkmatter”.

PopulationIIIstars,dudsupernovae,supernovae,oxygendwarfsInprestellartimessmallperturbationscoolbyradiatinginHD,LiH,andotherlightmoleculesandstarttocollapse.Iftheperturbationsaretoomassiveorhavetoomuchangularmomentum,theycannotsuccessfullycollapsetoformastar.Atsomethresholdofmassorangularmomentum,asmallperturbation(>1000M⊙)cancollapsebysomehowejectingenoughmassandangularmomentumtoproduceaPopulationIIIstarof,say,200M⊙thatisrapidlyrotatingandoblate.Asitevolves,thestarcontinuestoloseasignificantfractionofitsmassandangularmomentumthrougharadiatively-drivenwindfromthelooselyboundmassattheequator.Thestarproducesahugeprolate“Stromgrensphere”.Thecoreofthestarisrapidlyrotating,oblate,andhotterandfasterburningatthe

1polesandalongtheaxisthanintheequatorialplane.Thereisastrongmeridionalcirculationthatmixesinfreshfuel.Thestarradiatesabout1051ergs/M⊙overitslifetimethatisonlyontheorderof105years.Itburnstoanoxygencore,butthen,becauseoftherapidrotation,theoblateness,andtherapidevolution,thestarcannotstablycollapse.Itfliesapartintheattempt.Itexplodeswith,say,10−3oftheenergyofasupernovaandproducesejectathatmoveatonly103kms−1insteadof3×104kms−1.Itisadudthatproduces,say,25M⊙ofoxygen,unburneddregsoflighterelements,noheavierelements,andnoremnant.Theejectamixwiththepreviouslylostmassandwiththesurroundingprimordialgas,butmuchmoreslowlythanwouldasupernovaremnant.Largerperturbationsproduce(several)smallerPopulationIIIstarswithlessangularmomentum.Oneofthesestars,with150to100M⊙,evolvesmoreslowlyandstablythanamoremassivestar.Itislessrapidlyrotatingandlessoblate.Itlosesasignificantfractionofitsmassandangularmomentumthrougharadiatively-drivenwindattheequator.Itproducesaprolate“Stromgrensphere”.Thestarradiatesabout1051ergs/M⊙overitslifetimethatisontheorderof106to107years.Itmayalsobeadud,butitlikelyproducesasupernovawithironoralphaelements,orboth,andleavesbehindablackhole.WhenradiationfromaPopulationIIIstarhitsanoxygenblobfromadudsupernova,itcompressesthegasandthegasradiatesinOHandH2Otocoolrapidly.Ultravioletradiationfromthestarisdown-convertedtovisible-,infrared-,andradio-lineradiationthatcannotbeabsorbedbytheprimordialgassurroundingtheoxygenblobbutisstronglyabsorbedwithintheblob(andbyotherblobs).Anyotherelementspresentfromthedudexplosionaddtothemolecularmixandincreasethelineopacity.Theilluminatedblobsurfaceformsawalloflowmassoxygen-dwarfstars.Theprocessrepeatsforminglayersofstars.Radiatively-drivenimplosionsaredescribedinKurucz(2000).Starsformedinthiswayhavenotyetevolvedofftheirmainsequenceatthepresenttime.IhavecomputedATLAS12(Kurucz1995;2005)modelatmospheresforoxygendwarfswithTeff3500Kand3000K;logg=5;forfractionalabundancesbynumberH=.911,He=.089,logLi=-10,logO=-4,-5,-6.ThepinchofLiaddsafewelectrons.Figure1showsthetemperature-RosselandopticaldepthrelationscomparedtothoseforPopulationIandextremePopulationIIMdwarfsofthesameTeffandgravity.Notethatthesearephotosphericmodelswithnotemperatureminimumandnochromosphere.ThetemperaturedistributionsareradicallydifferentfromthoseofPopulationIandPopulationIIstars.Figures2through7showtheenergydistributionsforthesemodels.Strongwaterabsorptionintheinfraredoftheoxygendwarfsforcesthestarstoradiateinthevisibletomaintainenergybalance.OxygendwarfshaveanearlyfeaturelessspectruminthevisibleexceptforHαwhichwouldbeaffectedbyachromosphere.Iftheparentdudsupernovahadsomecarbon,theoxygendwarfdaughtersbindthecarboninCOwhichproducesadditionalabsorptionintheinfrared.Lettherebe,say,106dudsupernovaeperlargeprotogalaxy.Theprotogalaxiesbecomefullofoxygenblobs.Lettherebe,say,106PopulationIIIstarssmaller