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Publié par | technische_universitat_munchen |
Publié le | 01 janvier 2010 |
Nombre de lectures | 17 |
Langue | English |
Poids de l'ouvrage | 4 Mo |
Extrait
TechnischeUniversita¨tMu¨nchen
PhysikDepartment
Max-Planck-Institutfu¨rAstrophysik
Relativisticsimulationsof
compactobjectmergers
fornucleonicmatterand
strangequarkmatter
AndreasOttmarBauswein
Vollsta¨ndigerAbdruckdervonderFakulta¨tfu¨rPhysikderTechnischeUniversita¨tMu¨nchen
zurErlangungdesakademischenGradeseines
DoktorsderNaturwissenschaften(Dr.rer.nat.)
genehmigtenDissertation.
Vorsitzender:Univ.-Prof.Dr.R.Kru¨cken
Pru¨ferderDissertation:
1.Priv.-Doz.Dr.H.-Th.Janka
2.Univ.-Prof.Dr.W.Weise
DieDissertationwurdeam25.11.2009beiderTechnischenUniversita¨tMu¨nchen
eingereichtunddurchdieFakulta¨tfu¨rPhysikam29.01.2010angenommen.
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3
Contents
1.Introduction7
1.1.Physicalcontext................................7
1.2.Observationalconsequences.........................9
1.2.1.Gravitational-wavesignals......................9
1.2.2.Gamma-raybursts..........................10
1.2.3.Nucleosynthesisaspects.......................11
1.2.4.Signaturesofstrangequarkmatter.................11
1.3.Modelingcompactstarmergers.......................12
1.4.Neutronstar-blackholemergers.......................14
1.5.Goalsandoutlineofthethesis........................15
1.6.Conventionsandnotations..........................16
2.Physicalmodelandnumericalimplementation17
2.1.Relativisticsmoothparticlehydrodynamicsandtheconformalatness
approximation.................................17
2.1.1.Initialdata..............................22
2.2.Simulatingneutronstar-blackholemergers.................22
2.2.1.Blackholesinnumericalrelativity..................23
2.2.2.Punctureblackholeintheconformalatnessapproach......25
2.2.3.Furtheraspectsofsimulatingblackholes..............29
3.Equationofstateofhigh-densitymatter33
3.1.Nuclearequationsofstate..........................33
3.2.Strangequarkmatterequationsofstate..................35
3.3.Thermodynamicalpropertiesandstellarstructure.............36
3.4.Somecommentsonstrangequarkmatter..................40
4.Simulations43
4.1.Generaloverview...............................43
4.2.Binarieswith1.2Mand1.35M.....................47
4.3.Binarieswith1.35Mand1.35M.....................50
4.4.Binarieswith1.8Mand1.8M......................52
4.5.Thermaleects................................52
5.Gravitationalwaves55
5.1.Characteristicfeatures............................55
5.2.Binaryparameterdependence........................59
5
oCtnnets5.3.Equationofstatedependenceandthermaleects.............64
5.4.Occurrenceofapromptcollapse.......................65
5.5.Gravitational-waveluminosity........................67
6.Massejectionofstrangestarmergers
73
7.Simulationsofmixedbinaries79
7.1.Head-oncollisions...............................79
7.2.Quasi-equilibriumorbits...........................83
7.3.Mergingcompactstar-blackholebinaries..................84
8.Summary,conclusionsandoutlook
59
A.Thermaleectsinneutronstarmergersimulations99
A.1.Temperaturephenomenology.........................99
A.2.Approximatetreatmentofthermaleects..................103
B.Mass-radiusrelationsofneutronstars
6
111
1.Introduction
1.1.Physicalcontext
Starsmoremassivethan8solarmassesendtheirhydrostaticevolutionwithasupernova
explosion.Theremnantsofsucheventsareeitherablackhole(BH)forthemostmassive
progenitorstarsoracompactstar,commonlyreferredtoasneutronstar(NS).Thetrue
natureofthelatterhasremainedamysterysincethediscoveryoftheseobjects.Besides
acompositionofmainlyneutrons,moreexoticphaseshavebeenproposedtooccurin
compactstars[59,66].Theremayevenbethepossibilitythattheseobjectsareinreality
quarkstars.Accordingtothestrangematterhypothesis[25,164]amixtureofup,down
andstrangequarksmayformthetrueandabsolutegroundstateofmatterandifthis
hypothesisweretrue,compactstarswouldbeso-calledstrangestars(SSs)consistingof
thishigh-densitystrangequarkmatterratherthanNSmatter[59,66].Itturnsoutthat
SSsareinmanywayssimilartoNSs,forexampleinthemassrangeandcompactness,
andthereforetheycanbeconsideredasanalternativetoNSsinaccordancewiththe
observedpropertiesofknowncompactstars[3,59,65,66,160].Throughoutthisthesis
thetermcompactstarreferstoeitheraNSoraSS.
Theoreticalconsiderationscannotexcludethestrangematterhypothesisandthusthe
existenceofSSsbecauseofuncertaintiesontheequationofstate(EoS)ofhigh-density
matterandthephenomenonofquarkconnement[59,66,159,160].Also,theEoSof
ordinaryNSmatterabovenuclearsaturationdensity,2.71014g/cm3,isuncertain
becauseofmanydicultiesintreatingthenuclearmany-bodyproblem[66,89,159].
Furthermore,severalnuclearparameters,whichareusedintheoreticaldescriptions,are
notwellmeasured.Theseobservationaldataaredeterminedatdensitieswhichare
accessiblebylaboratoryexperiments,butathigherdensitiesrelevantforNSstheycan
onlybeextrapolated.Becauseofthisignoranceofthenatureofthetruehigh-density
EoSmanydierentEoSswereproposed,employingdierentmicrophysicalmodelsand
adoptingvariousexperimentaldata.
Toconstraintheuncertaintiesofthephysicsofcompactstars,astronomicalobserva-
tionsprovideauniquepossibilityandopenthefantasticavenuetostudynuclearand
particlephysicsatcelestialobjectsasaninterplaybetweenvariouseldsofresearch.
Somemassesofcompactstarsareknownverywellbytimingthearrivalofradiosignals
ofpulsarsasmembersinbinarysystems[150].Allotherstellarpropertiesareratherun-
certain,includingradiusmeasurements.Thisisunfortunate,becauseforinstanceonly
onewelldeterminedpointofthemass-radiusrelation,whichisentirelygivenbythe
EoS,wouldputtightconstraintsontheEoSandwouldeventuallyalsodecidewhether
SSsexist[66,89].
7
1.nItroudtcoinFigure1.1.:Cumulativeshiftoftheperiastrondemonstratingtheorbitaldecayofthe
binarypulsar1913+16duetotheemissionofGWs.InNewtoniangravitynosucheect
ispredicted(horizontalsolidline).Figuretakenfrom[161].
Thisthesisisintendedtoexploretheastrophysicalconsequencesofdierenthigh-
densityEoSsinthecontextofcompactstarmergersincludingmodelsthatdescribe
absolutelystablestrangequarkmatter.Inparticular,itisexaminedifthemergersof
SSscouldyieldobservationalsignaturesthatallowonetodistinguishthemfromcolliding
.sSNAtthetimeofwritingthisthesisabouttenbinariescomposedoftwocompactstarsare
knowninourgalaxy(seethecompilationin[117,150]),amongthemthefamousHulse-
Taylorpulsar[161].Theobservationofthisbinaryprovedforthersttimeindirectly
theexistenceofgravitationalwaves(GWs)(seeFig.1.1),whichwerepredictedby
Einsteinalreadyin1918[44]butarestillwaitingfortheirdirectdetection[33].The
orbitalparametersinthedoublecompactstarsystemscanbemeasuredveryprecisely
byradiotelescopes,anditisfoundthattheorbitsofthesebinariesdecayinaway
8
12..Osbreavtoianlocsnqeeucnsepredictedbygeneralrelativity[86,95].ThisisduetotheemissionofGWs,whichcarry
awayenergyandangularmomentum.Thedecreaseoftheorbitalseparationonatime
scaleofabout100-1000Myrs