6河外星系-3.ppt

2020/6/13,xkong,1,第六章河外星系,研究历史星系分类星系测量特殊星系：银河系星系团星系演化,2020/6/13,xkong,2,LEARNINGGOALS,DescribetheoverallstructureoftheMilkyWayGalaxyandspecifyhowthevariousregionsdifferfromoneanother.DescribetheorbitalpathsofstarsindifferentregionsoftheGalaxyandexplainhowthesemotionsareaccountedforbyourunderstandingofhowtheGalaxyformed.Discusssomepossibleexplanationsfortheexistenceofthespiralarmsobservedinourownandmanyothergalaxies.DescribesomeofthephenomenaobservedatthecenterofourGalaxy.,2020/6/13,xkong,3,本章内容,银河系外貌银河系结构银河系物质银河系形成银河系中心,2020/6/13,xkong,4,TheMilkyWay银河系,Theresnoplacelikehome！,2020/6/13,xkong,5,2020/6/13,xkong,6,Whatdoesourgalaxylooklike?,2020/6/13,xkong,7,TheMilkyWaygalaxyappearsinourskyasafaintbandoflight,2020/6/13,xkong,8,DustygascloudsobscureourviewbecausetheyabsorbvisiblelightThisistheinterstellarmediumthatmakesnewstarsystems,2020/6/13,xkong,9,Weseeourgalaxyedge-onPrimaryfeatures:disk,bulge,halo,globularclusters,2020/6/13,xkong,10,IfwecouldviewtheMilkyWayfromabovethedisk,wewouldseeitsspiralarms,2020/6/13,xkong,11,银河系结构,21011恒星、质量1012M，直径30kpc具有旋涡结构的盘状星系。主要成分：银盘(disk)(旋臂spiralarm)、核球(bulge)、银晕(halo)、银冕(corona),2020/6/13,xkong,12,2020/6/13,xkong,13,构成：星族I恒星、气体和尘埃直径：D30kpc厚度：h70-300pc,银河系的银盘,2020/6/13,xkong,14,银河系的旋臂结构,2020/6/13,xkong,15,天鹅臂,英仙臂,猎户臂,人马臂,盾牌南十字臂,矩尺臂,2020/6/13,xkong,16,核球(bulge)与银心(Galacticcenter),银心在人马座方向核球呈椭球形，大小约64kpc，恒星分布十分密集，数密度1,600ly-3,是银河系平均恒星密度的105倍,2020/6/13,xkong,17,ThecenteroftheGalaxyinradiowaves,2020/6/13,xkong,18,银晕(Galactichalo),球状星团年老的星族II恒星、以银心为中心球状分布，在椭圆轨道上绕银心旋转（V100kms-1），离银心最远距离达100kpc热气体弥漫的X射线辐射表明在银晕中存在大量的热气体暗物质:银晕中的不可见物质质量远远超过银河系可见物质质量,2020/6/13,xkong,19,银盘为pop.I恒星：年轻的、富金属恒星(疏散星团)银晕和核球中为星族II恒星：年老的、贫金属恒星,2020/6/13,xkong,20,Howdostarsorbitinourgalaxy?,2020/6/13,xkong,21,Starsinthediskallorbitinthesamedirectionwithalittleup-and-downmotion,2020/6/13,xkong,22,Orbitsofstarsinthebulgeandhalohaverandomorientations,2020/6/13,xkong,23,2020/6/13,xkong,24,2020/6/13,xkong,25,ThoughtQuestion,Whydoorbitsofbulgestarsbobupanddown(忽沉忽浮)?A.TheyrestucktointerstellarmediumB.GravityofdiskstarspullstowarddiskC.Halostarsknockthembackintodisk,2020/6/13,xkong,26,ThoughtQuestion,Whydoorbitsofbulgestarsbobupanddown(忽沉忽浮)?A.TheyrestucktointerstellarmediumB.GravityofdiskstarspullstowarddiskC.Halostarsknockthembackintodisk,2020/6/13,xkong,27,Sunsorbitalmotion(radiusandvelocity)tellsusmasswithinSunsorbit:1.0 x1011MSun,2020/6/13,xkong,28,OrbitalVelocityLaw,Theorbitalspeed(v)andradius(r)ofanobjectonacircularorbitaroundthegalaxytellsusthemass(Mr)withinthatorbit,2020/6/13,xkong,29,Whathavewelearned?,Whatdoesourgalaxylooklike?Ourgalaxyconsistsofadiskofstarsandgas,withabulgeofstarsatthecenterofthedisk,surroundedbyalargesphericalhaloHowdostarsorbitinourgalaxy?Starsinthediskorbitincirclesgoinginthesamedirectionwithalittleup-and-downmotionOrbitsofhaloandbulgestarshaverandomorientations,2020/6/13,xkong,30,Howisgasrecycledinourgalaxy?,Star-gas-starcycle:recyclesgasfromoldstarsintonewstarsystems,2020/6/13,xkong,31,High-massstarshavestrongstellarwindsthatblowbubblesofhotgas,2020/6/13,xkong,32,Lowermassstarsreturngastointerstellarspacethroughstellarwindsandplanetarynebulae,2020/6/13,xkong,33,X-raysfromhotgasinsupernovaremnantsrevealnewly-madeheavyelements,2020/6/13,xkong,34,SupernovaremnantcoolsandbeginstoemitvisiblelightasitexpandsNewelementsmadebysupernovamixintointerstellarmedium,2020/6/13,xkong,35,RadioemissioninsupernovaremnantsisfromparticlesacceleratedtonearlightspeedCosmicraysprobablycomefromsupernovae,2020/6/13,xkong,36,MultiplesupernovaecreatehugehotbubblesthatcanblowoutofdiskGascloudscoolinginthehalocanrainbackdownondisk,2020/6/13,xkong,37,MolecularcloudsinOrionComposition:MostlyH2About28%HeAbout1%COManyothermolecules,Atomichydrogengasformsashotgascools,allowingelectronstojoinwithprotonsMolecularcloudsformnext,aftergascoolsenoughtoallowtoatomstocombineintomolecules,2020/6/13,xkong,38,Gravityformsstarsoutofthegasinmolecularclouds,completingthestar-gas-starcycleRadiationfromnewlyformedstarsiserodingthesestar-formingclouds,2020/6/13,xkong,39,SummaryofGalacticRecycling,StarsmakenewelementsbyfusionDyingstarsexpelgasandnewelements,producinghotbubbles(106K)Hotgascools,allowingatomichydrogencloudstoform(100-10,000K)Furthercoolingpermitsmoleculestoform,makingmolecularclouds(30K)Gravityformsnewstars(andplanets)inmolecularclouds,GasCools,2020/6/13,xkong,40,ThoughtQuestion,Wherewillthegasbein1trillionyears(1012)?A.BlownoutofgalaxyB.StillrecyclingjustlikenowC.Lockedintowhitedwarfsandlow-massstars,2020/6/13,xkong,41,ThoughtQuestion,Wherewillthegasbein1trillionyears(1012)?A.BlownoutofgalaxyB.StillrecyclingjustlikenowC.Lockedintowhitedwarfsandlow-massstars,2020/6/13,xkong,42,Observestar-gas-starcycleoperatinginMWsdiskusingmanydifferentwavelengthsoflight,2020/6/13,xkong,43,Infraredlightrevealsstarswhosevisiblelightisblockedbygasclouds,Infrared,Visible,2020/6/13,xkong,44,X-raysareobservedfromhotgasaboveandbelowtheMilkyWaysdisk,X-rays,2020/6/13,xkong,45,Red:1-3keVGreen:3-5keVBlue:5-8keV,ChandraX-raySurveyoftheGalacticCenter,2020/6/13,xkong,46,21-cmradiowavesemittedbyatomichydrogenshowwheregashascooledandsettledintodisk,Radio(21cm),2020/6/13,xkong,47,Radiowavesfromcarbonmonoxide(CO)showlocationsofmolecularclouds,Radio(CO),2020/6/13,xkong,48,Long-wavelengthinfraredemissionshowswhereyoungstarsareheatingdustgrains,IR(dust),2020/6/13,xkong,49,Gammaraysshowwherecosmicraysfromsupernovaecollidewithatomicnucleiingasclouds,2020/6/13,xkong,50,Wheredostarstendtoforminourgalaxy?,2020/6/13,xkong,51,发射星云是受到附近炽热的恒星激发而发光的，这些恒星所发出的紫外线会电离星云内的氢气(Hregions)，令它们发光Ionizationnebulaearefoundaroundshort-livedhigh-massstars,signifyingactivestarformation,2020/6/13,xkong,52,反射星云:靠反射和散射近旁的亮星的光而变得明亮可见的星云。Reflectionnebulae如果尘埃云附近的恒星不是足够热，星光电离周围的星云发射星云当恒星足够亮，反射、散射光将很强，使得尘埃云可见反射星云反射星云是靠反射附近恒星的光线而发光的，呈蓝色,2020/6/13,xkong,53,Disk:Ionizationnebulae,bluestarsstarformation,Halo:Noionizationnebulae,nobluestarsnostarformation,2020/6/13,xkong,54,Muchofstarformationindiskhappensinspiralarms,WhirlpoolGalaxy,IonizationNebulaeBlueStarsGasClouds,Spiralarmsarewavesofstarformation,2020/6/13,xkong,55,SpiralarmsarewavesofstarformationGascloudsgetsqueezedastheymoveintospiralarmsSqueezingofcloudstriggersstarformationYoungstarsflowoutofspiralarms,2020/6/13,xkong,56,Whathavewelearned?,Howisgasrecycledinourgalaxy?Gasfromdyingstarsmixesnewelementsintotheinterstellarmediumwhichslowlycools,makingthemolecularcloudswherestarsformThosestarswilleventuallyreturnmuchoftheirmattertointerstellarspaceWheredostarstendtoforminourgalaxy?Activestar-formingregionscontainmolecularclouds,hotstars,andionizationnebulaeMuchofthestarformationinourgalaxyhappensinthespiralarms,2020/6/13,xkong,57,TheHistoryoftheMilkyWay,2020/6/13,xkong,58,HaloStars:0.02-0.2%heavyelements(O,Fe,),onlyoldstars,DiskStars:2%heavyelements,starsofallages,2020/6/13,xkong,59,HaloStars:0.02-0.2%heavyelements(O,Fe,),onlyoldstars,DiskStars:2%heavyelements,starsofallages,Halostarsformedfirst,thenstopped,Diskstarsformedlater,keptforming,2020/6/13,xkong,60,Howdidourgalaxyform?,2020/6/13,xkong,61,Ourgalaxyprobablyformedfromagiantgascloud,2020/6/13,xkong,62,Halostarsformedfirstasgravitycausedcloudtocontract,2020/6/13,xkong,63,Remaininggassettledintospinningdisk,2020/6/13,xkong,64,Starscontinuouslyformindiskasgalaxygrowsolder,Warning:Thismodelisoversimplified,2020/6/13,xkong,65,Detailedstudies:Halostarsformedinclumpsthatlatermerged,2020/6/13,xkong,66,(a)银河系可能形成于小星系的并合(b)早期银河系形态不规则，恒星分布和运动应该是随机的(不并合时)(c)下落的气体和尘埃形成银盘和，老恒星在银晕(并合时)(d)盘中新形成的恒星绕银河系中心转动,2020/6/13,xkong,67,Whathavewelearned?,Whatcluestoourgalaxyshistorydohalostarshold?Halostarsareallold,withasmallerproportionofheavyelementsthandiskstars,indicatingthatthehaloformedfirstHowdidourgalaxyform?Ourgalaxyformedfromahugecloudofgas,withthehalostarsformingfirstandthediskstarsforminglater,afterthegassettledintoaspinningdisk,2020/6/13,xkong,68,Whatliesinthecenterofourgalaxy?,2020/6/13,xkong,69,星系中心的射电辐射,星系中心的红外辐射,2020/6/13,xkong,70,星系中心的射电辐射,靠近中心的漩涡状气体,2020/6/13,xko