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1、DecipheringthenatureofdarkmatterBernardSadouletCenterforParticleAstrophysics,LawrenceBerkeleyNationalLaboratoryandPhysicsDepartment,UniversityofCalifornia,Berkeley,Berkeley,California94720[S0034-6861(99)05402-1]I.INTRODUCTIONdredsofgalaxiesthatconstituteri
2、chclustersareofteninexcessof1500km/s.SuchlargevaluesindicateevenThehistoryofphysicscanbeseenasthegradualdis-deeperpotentialwellsthanforgalaxies.Inmanyclusterscoveryofstructuresinvisibletothehumaneyeandthealargeamountofgasisdetectedthroughitsx-rayemis-instr
3、umentsofthetime.Thesestructuresareoftension,anditshightemperature('5keV)impliessimilarhintedat®rstbyindirectevidence,andnewinstrumen-darkmasses.Inthelastfewyears,athirdpieceofevi-tationhastobeinventedtofullyestablishtheirexis-dencehasbeengatheredthatalsopo
4、intstoaverylargetenceandtostudytheirproperties.Thesearchfortheamountofdarkmatterinclusters.Galaxyclustersgravi-darkmatterintheuniverserepresentsanarchetypaltationallylensthelightemittedbyquasarsand®eldgal-casestudyofsuchaprocess.Ittooknearly60yearsfromaxie
5、sinthebackground.Themappingofthemassdis-the®rstevidence(Zwicki,1933)forastronomerstotributionthroughthemanyarcletsseeninanumberofreachaconsensusthatthereisadarkcomponentwhichclustersindicatespotentialwellsqualitativelysimilartodominatesgravitybutcannotbese
6、en,asitneitheremitsthoseobservedwiththetwoothermethods.Thesedarknorabsorbslight.AsexplainedinSec.II,thedebatehasmatterdensityestimatesarecon®rmedbythecombina-nowshiftedtooneaboutitsnature,inparticulartionofmeasurementsofthegasmassfractioninclusterswhetherd
7、arkmatterismadeofordinarybaryonicmat-(typically20%)andestimatesofthebaryondensityterorwhethernewnonbaryoniccomponentsplayasig-fromprimordialnucleosynthesis(see,e.g.,Whiteetal.,ni®cantrole.Anumberofinnovativeattemptstodeci-1993).pherthisnaturehavebeenlaunch
8、ed.SectionIIIreviewsAtalargerscale,measurementsofvelocity¯owsandthesearchesforbaryonicformsofdarkmatterincludingcorrelationshintatevenlargeramountsofdarkmatter.theevidenceformassivehalocompactobjectsInthisvol
