天文学英文版PPT资料 (19)

UniverseEighthEditionRogerA.Freedman•WilliamJ.KaufmannIIICHAPTER24GalaxiesChapter24and26onlinequizzesdueThursday12/9SkipChapter27FinalExam–Monday12/13,5:30-7:30PMThefinalwillcoverchapters23,24and26only,sameformatasExams1-3LastHW!HowdidEdwinHubbleshowthatM31inAndromedaisadistantgalaxyandnotpartoftheMilkyWay?A.BymeasuringthedistancetoM31usingCepheidvariables.B.BymeasuringthedistancetoM31usingRRLyraevariables.C.BypreciselymeasuringtheparallaxofM31.D.ByobservinganovainM31.E.ByobservingasupernovainM31.Q24.7HowdidEdwinHubbleshowthatM31inAndromedaisadistantgalaxyandnotpartoftheMilkyWay?A.BymeasuringthedistancetoM31usingCepheidvariables.B.BymeasuringthedistancetoM31usingRRLyraevariables.C.BypreciselymeasuringtheparallaxofM31.D.ByobservinganovainM31.E.ByobservingasupernovainM31.A24.7WhichofthefollowingbestdescribestheHubblelawinitssimplestform?A.Therecessionalvelocityofagalaxyisproportionaltoitsdistancefromus.B.Therecessionalvelocityofagalaxyisinverselyproportionaltoitsdistancefromus.C.Thebrightnessofagalaxyisproportionaltoitsdistancefromus.D.Thebrightnessofagalaxyisinverselyproportionaltoitsdistancefromus.E.Thebrightnessofagalaxyisinverselyproportionaltoitscolor.Q24.10WhichofthefollowingbestdescribestheHubblelawinitssimplestform?A.Therecessionalvelocityofagalaxyisproportionaltoitsdistancefromus.B.Therecessionalvelocityofagalaxyisinverselyproportionaltoitsdistancefromus.C.Thebrightnessofagalaxyisproportionaltoitsdistancefromus.D.Thebrightnessofagalaxyisinverselyproportionaltoitsdistancefromus.E.Thebrightnessofagalaxyisinverselyproportionaltoitscolor.A24.10Inwhichofthefollowingtypesofgalaxieswouldyoubeleastlikelytofindanewly-formedstar?A.EllipticalB.SpiralC.IrregularD.Misleadingquestion—newly-formedstarscanbefoundinellipticals,spirals,andirregularsQ24.8Inwhichofthefollowingtypesofgalaxieswouldyoubeleastlikelytofindanewly-formedstar?A.EllipticalB.SpiralC.IrregularD.Misleadingquestion—newly-formedstarscanbefoundinellipticals,spirals,andirregularsA24.8KeyIdeasTheHubbleClassification:Galaxiescanbegroupedintofourmajorcategories:spirals,barredspirals,ellipticals,andirregulars.Thedisksofspiralandbarredspiralgalaxiesaresitesofactivestarformation.Ellipticalgalaxiesarenearlydevoidofinterstellargasanddust,andsostarformationisseverelyinhibited.Lenticulargalaxiesareintermediatebetweenspiralandellipticalgalaxies.Irregulargalaxieshaveill-defined,asymmetricalshapes.Theyareoftenfoundassociatedwithothergalaxies.KeyIdeasDistancetoGalaxies:Standardcandles,suchasCepheidvariablesandthemostluminoussupergiants,globularclusters,HIIregions,andsupernovaeinagalaxy,areusedinestimatingintergalacticdistances.TheTully-Fisherrelation,whichcorrelatesthewidthofthe21-cmlineofhydrogeninaspiralgalaxywithitsluminosity,canalsobeusedfordeterminingdistance.Amethodthatcanbeusedforellipticalgalaxiesisthefundamentalplane,whichrelatesthegalaxy’ssizetoitssurfacebrightnessdistributionandtothemotionsofitsstars.KeyIdeasTheHubbleLaw:ThereisasimplelinearrelationshipbetweenthedistancefromtheEarthtoaremotegalaxyandtheredshiftofthatgalaxy(whichisameasureofthespeedwithwhichitisrecedingfromus).ThisrelationshipistheHubblelaw,v=H0d.ThevalueoftheHubbleconstant,H0,isnotknownwithcertaintybutiscloseto73km/s/Mpc.KeyIdeasClustersandSuperclusters:Galaxiesaregroupedintoclustersratherthanbeingscatteredrandomlythroughouttheuniverse.Arichclustercontainshundredsoreventhousandsofgalaxies;apoorcluster,oftencalledagroup,maycontainonlyafewdozen.Aregularclusterhasanearlysphericalshapewithacentralconcentrationofgalaxies;inanirregularcluster,galaxiesaredistributedasymmetrically.KeyIdeasOurGalaxyisamemberofapoor,irregularclustercalledtheLocalGroup.Rich,regularclusterscontainmostlyellipticalandlenticulargalaxies;irregularclusterscontainspiral,barredspiral,andirregulargalaxiesalongwithellipticals.Giantellipticalgalaxiesareoftenfoundnearthecentersofrichclusters.KeyIdeasGalacticCollisionsandMergers:Whentwogalaxiescollide,theirstarspasseachother,buttheirinterstellarmediacollideviolently,eitherstrippingthegasanddustfromthegalaxiesortriggeringprolificstarformation.Thegravitationaleffectsduringagalacticcollisioncanthrowstarsoutoftheirgalaxiesintointergalacticspace.Galacticmergersmayoccur;alargegalaxyinarichclustermaytendtogrowsteadilythroughgalacticcannibalism,perhapsproducingintheprocessagiantellipticalgalaxy.KeyIdeasTheDark-MatterProblem:Theluminousmassofaclusterofgalaxiesisnotlargeenoughtoaccountfortheobservedmotionsofthegalaxies;alargeamountofunobservedmassmustalsobepresent.Thissituationiscalledthedark-matterproblem.Hotintergalacticgasesinrichclustersaccountforasmallpartoftheunobservedmass.ThesegasesaredetectedbytheirX-rayemission.Theremainingunobservedmassisprobablyintheformofdark-matterhalosthatsurroundthegalaxiesintheseclusters.Gravitationallensingofremotegalaxiesbyaforegroundclusterenablesastronomerstogleaninformationaboutthedistributionofdarkmatterintheforegroundcluster.KeyIdeasFormationandEvolutionofGalaxies:Observationsindicatethatgalaxiesarosefrommergersofseveralsmalle