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1、ComputerAnimationofAccretionofNeutronStarsWangKeiSo,HoYinLaw,HiuPanTangS.K.HTsangShiuTimSecondarySchoolAbstractIntheresearch,binarysystemsconsistingofneutronstarwerestudied.Afterreviewingthebasicknowledgeofneutronstars,wewroteacomputerprogramtoanimateandvisualizetheaccretionprocessonatwo-dim
2、ensionalplane.1.IntroductionAneutronstarcanexistinabinarystarsystem.Sincetheneutronstarhasaveryhighdensity,itsgravitationalattractiononitscompanionstarissostrong.Matterfromthecompanionstarislostbybeingattractedtotheneutronstar.Thisphenomenoniscalledaccretion.Duringaccretion,thenormalcompanio
3、nstarisdistortedbytheneutronstar’sgravityandthefluidmaterialonitisabsorbedbytheneutronstar.Beforeoftheenergyofthefluidmaterialisconvertedtoradiationenergyemittedfromtheneutronstar,thesematerialswilllooparoundtheneutronstartoformanaccretiondisc,untilmostofthematerialisabsorbedbythenormalcompa
4、nionstar.2.ModelofaBinarySystemContainingaNeutronStarandaRedGiantInordertomaketheanimationmoreconvincing,wehavemadereferencetothebinarystarsystem‘HerculesX-1’,whichwasobservedtocontainaneutronstaranditscompanionredgiant.Wehavemadeuseofitsdatainourcomputeranimation.Redgiantm1II1CenterofmassI0
5、Neutronstarm0Asshowninthefigure,thedistancesoftheneutronstarandredgiantfromthecentreofmasssatisfytheequationsI0+I1=Iandm0I0=m1I1.Hencetheyaregivenbymm10I=IandI=I.01m+mm+m0101ndFortheneutronstarandredgianttoexhibitcircularmotion,theirvelocitiesaregivenbyNewton’s2law,22GmmvGmmv010011=mand=m.20
6、21II0II1HenceGmIGmI1001v=andv=.0212IIChoosingthecentreofmassastheorigin,thepositionsareNeutronstar:(0,–I0).Redgiant:(0,I1).ThevelocitiesareNeutronstar:(v0,0).RedGiant:(–v1,0).3.Assumptionsandtheoryappliedonthemodelofaccretion1.Theredgiantismadeupofafluidofparticles.Thedensityofthefluiddecrea
7、sesfromitsinteriortothecore.Wefirstassumethetotalmassoftheredgiantisconcentratedatthecentreofmassoftheredgiant.Followingthisassumption,wenextassumethatthefluidparticlesonthesurface,whichareverylightwithrespecttothecentreoftheredgiant,havenointeract
