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∙t

∙e

Partofaserieson

Physicalcosmology

∙Universe

∙BigBang

∙Ageoftheuniverse

∙Chronologyoftheuniverse

Earlyuniverse[show]

Expandinguniverse[show]

Structureformation[show]

Futureofuniverse[show]

Components[hide]

∙Lambda-CDMmodel

∙Darkenergy

History[show]

Scientists[show]

Socialimpact[show]

∙

Astronomyportal

Category:

Physicalcosmology

Estimateddistributionofmatterandenergyintheuniverse,today（top）andwhenthe 

CMB 

wasreleased（bottom）

In 

astronomy 

and 

cosmology, 

darkmatter 

isatypeof 

matter 

hypothesizedtoaccountforalargepartofthetotal 

massinthe 

universe.Darkmattercannotbeseendirectlywithtelescopes;

evidentlyitneither 

emits 

norabsorbslightorother 

electromagneticradiation 

atanysignificantlevel.[1] 

Instead,itsexistenceandpropertiesareinferredfromitsgravitationaleffectsonvisiblematter,radiation,andthelarge-scalestructureoftheuniverse.AccordingtothePlanckmissionteam,andbasedonthe 

standardmodelofcosmology,thetotal 

mass–energy 

ofthe 

universe 

contains4.9%ordinarymatter,26.8%darkmatterand68.3% 

darkenergy.[2][3][4] 

Thus,darkmatterisestimatedtoconstitute84.5%ofthetotalmatterintheuniverseand26.8%ofthetotalcontentoftheuniverse.[5]

Darkmattercametotheattentionofastrophysicistsduetodiscrepanciesbetweenthemassoflargeastronomicalobjectsdeterminedfromtheirgravitationaleffectsandthemasscalculatedfromthe"

luminousmatter"

theycontain:

stars,gas,anddust.Itwasfirstpostulatedby 

JanOort 

in1932toaccountfortheorbitalvelocitiesofstarsinthe 

MilkyWay 

andby 

FritzZwicky 

in1933toaccountforevidenceof"

missingmass"

intheorbitalvelocitiesof 

galaxies 

in 

clusters.Subsequently,manyotherobservationshaveindicatedthepresenceofdarkmatterintheuniverse,includingtherotationalspeedsofgalaxies 

by 

VeraRubin,[6] 

inthe1960s–1970s, 

gravitationallensing 

ofbackgroundobjectsbygalaxyclusterssuchasthe 

BulletCluster,thetemperaturedistributionofhotgasingalaxiesandclustersofgalaxies,andmorerecentlythepatternofanisotropiesinthe 

cosmicmicrowavebackground.Accordingtoconsensusamongcosmologists,darkmatteriscomposedprimarilyofanotyetcharacterizedtypeof 

subatomicparticle.[7][8] 

Thesearchforthisparticle,byavarietyofmeans,isoneofthemajoreffortsin 

particlephysics 

today.[9]

Althoughtheexistenceofdarkmatterisgenerallyacceptedbythemainstreamscientificcommunity,thereisnogenerallyagreeddirectdetectionofit.Othertheories,including 

MOND 

TeVeS,aresomealternativetheoriesofgravityproposedtotrytoexplaintheanomaliesforwhichdarkmatterisintendedtoaccount.

Contents

[hide] 

∙1 

Overview

∙2 

Baryonicandnonbaryonicdarkmatter

∙3 

Observationalevidence

o3.1 

Galaxyrotationcurves

o3.2 

Velocitydispersionsofgalaxies

o3.3 

Galaxyclustersandgravitationallensing

o3.4 

Cosmicmicrowavebackground

o3.5 

Skysurveysandbaryonacousticoscillations

o3.6 

TypeIasupernovaedistancemeasurements

o3.7 

Lyman-alphaforest

o3.8 

Structureformation

∙4 

Historyofthesearchforitscomposition

o4.1 

Colddarkmatter

o4.2 

Warmdarkmatter

o4.3 

Hotdarkmatter

o4.4 

Mixeddarkmatter

∙5 

Detection

o5.1 

Directdetectionexperiments

o5.2 

Indirectdetectionexperiments

∙6 

Alternativetheories

o6.1 

Modifiedgravitylaws

∙7 

Popularculture

∙8 

Seealso

∙9 

References

∙10 

Furtherreading

∙11 

Externallinks

Overview[edit]

Darkmatter'

sexistenceisinferredfrom 

gravitational 

effectsonvisiblematterand 

ofbackgroundradiation,andwasoriginallyhypothesizedtoaccountfordiscrepanciesbetweencalculationsofthemassof 

galaxies,clustersofgalaxiesandtheentireuniversemadethrough 

dynamical 

generalrelativistic 

means,andcalculationsbasedonthemassofthevisible"

luminous"

mattertheseobjectscontain:

stars 

andthegasanddustofthe 

interstellarand 

intergalactic 

medium.[1]

Themostwidelyacceptedexplanationforthesephenomenaisthatdarkmatterexistsandthatitismostprobably[7]composedof 

weaklyinteractingmassiveparticles 

（WIMPs）thatinteractonlythroughgravityandthe 

weakforce.Alternativeexplanationshavebeenproposed,andthereisnotyetsufficientexperimentalevidencetodeterminewhichiscorrect.Manyexperimentstodetectproposeddarkmatterparticlesthroughnon-gravitationalmeansareunderway.[9]

Accordingtoobservationsofstructureslargerthan 

starsystems,aswellas 

BigBang 

cosmologyinterpretedundertheFriedmannequations 

andthe 

Friedmann–Lemaî

tre–Robertson–Walkermetric,darkmatteraccountsfor26.8%ofthe 

mass-energy 

contentofthe 

observableuniverse.Incomparison,ordinary（baryonic）matteraccountsforonly4.9%ofthemass-energycontentoftheobservableuniverse,withtheremainderbeingattributableto 

darkenergy.[4] 

Fromthesefigures,matteraccountsfor31.7%ofthemass-energycontentoftheuniverse,and84.5%ofthematterisdarkmatter.[5]

Darkmatterplaysacentralroleinstate-of-the-artmodelingofcosmic 

structureformation 

Galaxyformationandevolution 

andhasmeasurableeffectsonthe 

anisotropies 

observedinthe 

cosmicmicrowavebackground.Alltheselinesofevidencesuggestthatgalaxies,clustersofgalaxies,andtheuniverseasawholecontainfarmorematterthanthatwhichinteractswithelectromagneticradiation.[10]

Importantasdarkmatteristhoughttobeinthecosmos,directevidenceofitsexistenceandaconcreteunderstandingofitsnaturehaveremainedelusive.Thoughthetheoryofdarkmatterremainsthemostwidelyacceptedtheorytoexplaintheanomaliesinobservedgalacticrotation,somealternativetheoreticalapproacheshavebeendevelopedwhichbroadlyfallintothecategoriesofmodifiedgravitationallawsandquantumgravitationallaws.[11]

Baryonicandnonbaryonicdarkmatter[edit]

Fermi-LAT 

observationsofdwarfgalaxiesprovidenewinsightsondarkmatter.

Therearethreeseparatelinesofevidencethatthemajorityofdarkmatterisnotmadeofbaryons,ordinarymatterincludingprotons,electronsandatoms:

∙Thetheoryof 

BigBangnucleosynthesis,whichveryaccuratelypredictstheobserved 

abundanceofthechemicalelements,[12] 

predictsthatbaryonicmatteraccountsforaround4–5percentofcriticaldensityoftheUniverse.Incontrast,evidencefrom 

large-scalestructure 

andotherobservationsindicatesthatthetotalmatterdensityissubstantiallyhigherthanthis.

∙Largeastronomicalsearchesforgravitational 

microlensing,includingtheMACHO,EROSandOGLEprojects,haveshownthatonlyasmallfractionofthedarkmatterintheMilkyWaycanbehidingindarkcompactobjects;

theexcludedrangecoversobjectsabovehalftheEarth'

smassupto30solarmasses,excludingnearlyalltheplausiblecandidates.

∙Detailedanalysisofthesmallirregularities（anisotropies）inthe 

cosmicmicrowavebackground 

observedbyWMAP 

Planck 

showsthataroundfive-sixthsofthetotalmatterisinaformwhichdoesnotinteractsignificantlywithordinarymatterorphotons.

Asmallproportionofdarkmattermaybe 

baryonicdarkmatter:

astronomicalbodies,suchas 

massivecompacthaloobjects,thatarecomposedofordinarymatterbutwhichemitlittleornoelectromagneticradiation.StudyofnucleosynthesisintheBigBangproducesanupperboundontheamountofbaryonicmatterintheuniverse,[13]whichindicatesthatthevastmajorityofdarkmatterintheuniversecannotbe 

baryons,andthusdoesnotform 

atoms.Italsocannotinteractwithordinarymattervia 

electromagneticforces;

inparticular,darkmatterparticlesdonotcarryany 

electriccharge.

Candidatesfornonbaryonicdarkmatterarehypotheticalparticlessuchas 

axions,or 

supersymmetric 

particles;

neutrinoscanonlyformasmallfractionofthedarkmatter,duetolimitsfrom 

andhigh-redshiftgalaxies.Unlikebaryonicdarkmatter,nonbaryonicdarkmatterdoesnotcontributetotheformationofthe 

elements 

intheearlyuniverse（"

BigBangnucleosynthesis"

）[7] 

andsoitspresenceisrevealedonlyviaitsgravitationalattraction.Inaddition,iftheparticlesofwhichitiscomposedaresupersymmetric,theycanundergo 

annihilation 

interactionswiththemselves,possiblyresultinginobservableby-productssuchas 

gammarays 

andneutrinos（"

indirectdetection"

）.[14]

Nonbaryonicdarkmatterisclassifiedintermsofthemassoftheparticle（s）thatisassumedtomakeitup,and/orthetypicalvelocitydispersionofthoseparticles（sincemoremassiveparticlesmovemoreslowly）.Therearethreeprominenthypothesesonnonbaryonicdarkmatter,called 

colddarkmatter 

（CDM）, 

warmdarkmatter 

（WDM）,and 

hotdarkmatter 

（HDM）;

somecombinationoftheseisalsopossible.Themostwidelydiscussedmodelsfornonbaryonicdarkmatterarebasedonthecolddarkmatterhypothesis,andthecorrespondingparticleismostcommonlyassumedtobea 

weaklyinteractingmassiveparticle 

（WIMP）.Hotdarkmattermayinclude（massive）neutrinos,butobservationsimplythatonlyasmallfracti