2025/8/15xkong@1第六章

河外星系研究歷史星系分類

星系測(cè)量特殊星系：銀河系

星系團(tuán)

星系演化/~xkong/introast2025/8/15xkong@2LEARNINGGOALS

DescribetheoverallstructureoftheMilkyWayGalaxyandspecifyhowthevariousregionsdifferfromoneanother.DescribetheorbitalpathsofstarsindifferentregionsoftheGalaxyandexplainhowthesemotionsareaccountedforbyourunderstandingofhowtheGalaxyformed.Discusssomepossibleexplanationsfortheexistenceofthespiralarmsobservedinourownandmanyothergalaxies.DescribesomeofthephenomenaobservedatthecenterofourGalaxy.2025/8/15xkong@3本章內(nèi)容銀河系外貌銀河系結(jié)構(gòu)銀河系物質(zhì)銀河系形成銀河系中心2025/8/15xkong@4TheMilkyWay銀河系There’snoplacelikehome！2025/8/15xkong@52025/8/15xkong@6Whatdoesourgalaxylooklike?2025/8/15xkong@7TheMilkyWaygalaxyappearsinourskyasafaintbandoflight2025/8/15xkong@8DustygascloudsobscureourviewbecausetheyabsorbvisiblelightThisistheinterstellarmediumthatmakesnewstarsystems2025/8/15xkong@9Weseeourgalaxyedge-onPrimaryfeatures:disk,bulge,halo,globularclusters2025/8/15xkong@10IfwecouldviewtheMilkyWayfromabovethedisk,wewouldseeitsspiralarms2025/8/15xkong@11銀河系結(jié)構(gòu)～2×1011恒星、質(zhì)量~1012M⊙，直徑~30kpc具有旋渦結(jié)構(gòu)的盤狀星系。

主要成分：銀盤(disk)(旋臂spiralarm)、

核球(bulge)、

銀暈(halo)、銀冕(corona)2025/8/15xkong@122025/8/15xkong@13構(gòu)成：星族I恒星、氣體和塵埃

直徑：D~30kpc厚度：h~70-300pc銀河系的銀盤2025/8/15xkong@14銀河系的旋臂結(jié)構(gòu)2025/8/15xkong@15天鵝臂英仙臂獵戶臂人馬臂盾牌－南十字臂矩尺臂2025/8/15xkong@16核球(bulge)與銀心(Galacticcenter)銀心在人馬座方向核球呈橢球形，大小

約6×4kpc，恒星分布十分密集，數(shù)密度~1,600ly-3,是銀河系平均恒星密度的105倍2025/8/15xkong@17ThecenteroftheGalaxyinradiowaves2025/8/15xkong@18銀暈(Galactichalo)球狀星團(tuán)

年老的星族II恒星、以銀心為中心球狀分布，

在橢圓軌道上繞銀心旋轉(zhuǎn)（V~100kms-1），離銀心最遠(yuǎn)距離達(dá)100kpc熱氣體彌漫的X射線輻射表明在銀暈中存在大量的熱氣體暗物質(zhì):銀暈中的不可見物質(zhì)質(zhì)量遠(yuǎn)遠(yuǎn)超過(guò)銀河系可見物質(zhì)質(zhì)量2025/8/15xkong@19銀盤為pop.I恒星：年輕的、富金屬恒星(疏散星團(tuán))銀暈和核球中為星族II恒星：年老的、貧金屬恒星2025/8/15xkong@20Howdostarsorbitinourgalaxy?2025/8/15xkong@21Starsinthediskallorbitinthesamedirectionwithalittleup-and-downmotion2025/8/15xkong@22Orbitsofstarsinthebulgeandhalohaverandomorientations2025/8/15xkong@232025/8/15xkong@242025/8/15xkong@25ThoughtQuestionWhydoorbitsofbulgestarsbobupanddown(忽沉忽浮

)?A.They’restucktointerstellarmediumB.GravityofdiskstarspullstowarddiskC.Halostarsknockthembackintodisk

2025/8/15xkong@26ThoughtQuestionWhydoorbitsofbulgestarsbobupanddown(忽沉忽浮

)?A.They’restucktointerstellarmediumB.GravityofdiskstarspullstowarddiskC.Halostarsknockthembackintodisk

2025/8/15xkong@27Sun’sorbitalmotion(radiusandvelocity)tellsusmasswithinSun’sorbit:1.0x1011

MSun2025/8/15xkong@28OrbitalVelocityLawTheorbitalspeed(v)andradius(r)ofanobjectonacircularorbitaroundthegalaxytellsusthemass(Mr)withinthatorbit2025/8/15xkong@29Whathavewelearned?Whatdoesourgalaxylooklike?Ourgalaxyconsistsofadiskofstarsandgas,withabulgeofstarsatthecenterofthedisk,surroundedbyalargesphericalhaloHowdostarsorbitinourgalaxy?Starsinthediskorbitincirclesgoinginthesamedirectionwithalittleup-and-downmotionOrbitsofhaloandbulgestarshaverandomorientations2025/8/15xkong@30Howisgasrecycledinourgalaxy?Star-gas-starcycle:recyclesgasfromoldstarsintonewstarsystems2025/8/15xkong@31High-massstarshavestrongstellarwindsthatblowbubblesofhotgas2025/8/15xkong@32Lowermassstarsreturngastointerstellarspacethroughstellarwindsandplanetarynebulae

2025/8/15xkong@33X-raysfromhotgasinsupernovaremnantsrevealnewly-madeheavyelements2025/8/15xkong@34SupernovaremnantcoolsandbeginstoemitvisiblelightasitexpandsNewelementsmadebysupernovamixintointerstellarmedium2025/8/15xkong@35RadioemissioninsupernovaremnantsisfromparticlesacceleratedtonearlightspeedCosmicraysprobablycomefromsupernovae2025/8/15xkong@36MultiplesupernovaecreatehugehotbubblesthatcanblowoutofdiskGascloudscoolinginthehalocanrainbackdownondisk2025/8/15xkong@37MolecularcloudsinOrionComposition:MostlyH2About28%HeAbout1%COManyothermoleculesAtomichydrogengasformsashotgascools,allowingelectronstojoinwithprotonsMolecularcloudsformnext,aftergascoolsenoughtoallowtoatomstocombineintomolecules2025/8/15xkong@38Gravityformsstarsoutofthegasinmolecularclouds,completingthestar-gas-starcycleRadiationfromnewlyformedstarsiserodingthesestar-formingclouds2025/8/15xkong@39SummaryofGalacticRecyclingStarsmakenewelementsbyfusionDyingstarsexpelgasandnewelements,producinghotbubbles(~106K)Hotgascools,allowingatomichydrogencloudstoform(~100-10,000K)Furthercoolingpermitsmoleculestoform,makingmolecularclouds(~30K)Gravityformsnewstars(andplanets)inmolecularcloudsGasCools2025/8/15xkong@40ThoughtQuestionWherewillthegasbein1trillionyears(10^12)?A.BlownoutofgalaxyB.StillrecyclingjustlikenowC.Lockedintowhitedwarfsandlow-massstars

2025/8/15xkong@41ThoughtQuestionWherewillthegasbein1trillionyears(10^12)?A.BlownoutofgalaxyB.StillrecyclingjustlikenowC.Lockedintowhitedwarfsandlow-massstars

2025/8/15xkong@42Observestar-gas-starcycleoperatinginMW’sdiskusingmanydifferentwavelengthsoflight2025/8/15xkong@43InfraredlightrevealsstarswhosevisiblelightisblockedbygascloudsInfraredVisible2025/8/15xkong@44X-raysareobservedfromhotgasaboveandbelowtheMilkyWay’sdiskX-rays2025/8/15xkong@45Red:1-3keV

Green:3-5keV

Blue:5-8keVChandraX-raySurveyoftheGalacticCenter2025/8/15xkong@4621-cmradiowavesemittedbyatomichydrogenshowwheregashascooledandsettledintodiskRadio(21cm)2025/8/15xkong@47Radiowavesfromcarbonmonoxide(CO)showlocationsofmolecularcloudsRadio(CO)2025/8/15xkong@48Long-wavelengthinfraredemissionshowswhereyoungstarsareheatingdustgrains

IR(dust)2025/8/15xkong@49Gammaraysshowwherecosmicraysfromsupernovaecollidewithatomicnucleiingasclouds2025/8/15xkong@50Wheredostarstendtoforminourgalaxy?2025/8/15xkong@51發(fā)射星云是受到附近熾熱的恒星激發(fā)而發(fā)光的，這些恒星所發(fā)出的紫外線會(huì)電離星云內(nèi)的氫氣(HⅡregions)，令它們發(fā)光

Ionizationnebulaearefoundaroundshort-livedhigh-massstars,signifyingactivestarformation2025/8/15xkong@52反射星云:靠反射和散射近旁的亮星的光而變得明亮可見的星云。Reflectionnebulae如果塵埃云附近的恒星不是足夠熱，星光電離周圍的星云

發(fā)射星云當(dāng)恒星足夠亮，反射、散射光將很強(qiáng)，使得塵埃云可見

反射星云反射星云是靠反射附近恒星的光線而發(fā)光的，呈藍(lán)色

2025/8/15xkong@53Disk:Ionizationnebulae,bluestars

starformationHalo:Noionizationnebulae,nobluestars

nostarformation2025/8/15xkong@54MuchofstarformationindiskhappensinspiralarmsWhirlpoolGalaxyIonizationNebulaeBlueStarsGasCloudsSpiralarmsarewavesofstarformation2025/8/15xkong@55SpiralarmsarewavesofstarformationGascloudsgetsqueezedastheymoveintospiralarmsSqueezingofcloudstriggersstarformationYoungstarsflowoutofspiralarms2025/8/15xkong@56Whathavewelearned?Howisgasrecycledinourgalaxy?Gasfromdyingstarsmixesnewelementsintotheinterstellarmediumwhichslowlycools,makingthemolecularcloudswherestarsformThosestarswilleventuallyreturnmuchoftheirmattertointerstellarspaceWheredostarstendtoforminourgalaxy?Activestar-formingregionscontainmolecularclouds,hotstars,andionizationnebulaeMuchofthestarformationinourgalaxyhappensinthespiralarms2025/8/15xkong@57TheHistoryoftheMilkyWay2025/8/15xkong@58HaloStars:0.02-0.2%heavyelements(O,Fe,…),onlyoldstarsDiskStars:2%heavyelements,starsofallages2025/8/15xkong@59HaloStars:0.02-0.2%heavyelements(O,Fe,…),onlyoldstarsDiskStars:2%heavyelements,starsofallagesHalostarsformedfirst,thenstoppedDiskstarsformedlater,keptforming2025/8/15xkong@60Howdidourgalaxyform?2025/8/15xkong@61Ourgalaxyprobablyformedfromagiantgascloud2025/8/15xkong@62Halostarsformedfirstasgravitycausedcloudtocontract2025/8/15xkong@63Remaininggassettledintospinningdisk2025/8/15xkong@64StarscontinuouslyformindiskasgalaxygrowsolderWarning:Thismodelisoversimplified2025/8/15xkong@65Detailedstudies:Halostarsformedinclumpsthatlatermerged2025/8/15xkong@66(a)銀河系可能形成于小星系的并合(b)早期銀河系形態(tài)不規(guī)則，恒星分布和運(yùn)動(dòng)應(yīng)該是隨機(jī)的(不并合時(shí))(c)下落的氣體和塵埃形成銀盤和，老恒星在銀暈(并合時(shí))(d)盤中新形成的恒星繞銀河系中心轉(zhuǎn)動(dòng)2025/8/15xkong@67Whathavewelearned?Whatcluestoourgalaxy’shistorydohalostarshold?Halostarsareallold,withasmallerproportionofheavyelementsthandiskstars,indicatingthatthehaloformedfirstHowdidourgalaxyform?Ourgalaxyformedfromahugecloudofgas,withthehalostarsformingfirstandthediskstarsforminglater,afterthegassettledintoaspinningdisk2025/8/15xkong@68Whatliesinthecenterofourgalaxy?2025/8/15xkong@69星系中心的射電輻射星系中心的紅外輻射2025/8/15xkong@70星系中心的射電輻射靠近中心的漩渦狀氣體2025/8/15xkong@71靠近中