ASTR 1120ASTR 1120General Astronomy:General Astronomy:Stars & GalaxiesStars & Galaxies!NNOUNCEMENTS• Homework #7 due today, by 5pm• Homework #8 due next Tue, Nov. 17, by 5pm• Midterm #3 on Thu, Nov.19• EXTRA OBSERVING NIGHTEXTRA OBSERVING NIGHT - THU 12th, from 8:30pm (20 students every 1/2 hr)Andromeda found to be far Andromeda found to be far outsideoutside Milky Way! Milky Way!••Edwin HubbleEdwin Hubble in 1924in 1924identifiedidentified CepheidsCepheids ininAndromeda (M33) Andromeda (M33) !!showed they were showed they were farfaroutsideoutside of Milky Way! of Milky Way!––““Island UniversesIsland Universes””••His first big discovery!His first big discovery!••But then he turned hisBut then he turned hisattention to attention to OTHEROTHERgalaxiesgalaxiesHubble using new Hubble using new 100100”” Hooker telescope Hooker telescopeat Mt. Wilson (above LA)at Mt. Wilson (above LA)REVIEWREVIEWv = Ho ! dVelocity ofRecession(Doppler Shift)Hubble’sConstantDistance(km/sec)(km/sec/Mpc)(Mpc)““HubbleHubble’’s Laws Law””velocityvelocitydistancedistanceREVIEWREVIEWBalloon analogy forBalloon analogy forexpanding universeexpanding universe••Each dot on theEach dot on the balloon can beballoon can bethought of as athought of as agalaxy.galaxy. As the balloonAs the balloonexpands, galaxiesexpands, galaxiesmove farther awaymove farther awayfrom each otherfrom each otherREVIEWREVIEWChapter 21: Galaxy EvolutionChapter 21: Galaxy Evolution• Observing galaxies at different redshifts(lookback times)!!• Allows us to assemble a sequence ofgalaxies showing birth and evolution!!• Check via computer models of gas,gravity and star formationThe Hubble Deep FieldThe Hubble Deep FieldSomegalaxiesveryyoung,when theUniversewas abouta tenth ofits currentage!Making of a Making of a spiral galaxyspiral galaxy••Start with a fairlyStart with a fairlyuniform cloud ofuniform cloud ofhydrogenhydrogen••Gravitational collapseGravitational collapseformsforms protogalacticprotogalacticcloudsclouds••First stars are born inFirst stars are born inthisthis spheroid spheroid (such(suchstars are billions ofstars are billions ofyears old years old !! ““fossilfossilrecordrecord””))REVIEWSmall variant in spiral making Small variant in spiral making ……••SeveralSeveral smallersmallerprotogalacticprotogalacticcloudsclouds maymayhave merged tohave merged toform a singleform a singlelarge galaxylarge galaxy••May explainMay explainvariations invariations inmetallicities metallicities ininthe halo starsthe halo starsREVIEWForming a Forming a diskdiskwith spiralwith spiral••As more materialAs more materialcollapses,collapses, angularangularmomentummomentum spins itspins itinto a diskinto a disk••Stars now formedStars now formedin in dense spiraldense spiralarmsarms –– disk starsdisk starsare younger!are younger!Angular momentum of protogalactic cloudimportant in spiral galaxy formationREVIEWMaking Making ellipticalsellipticals1.1.Higher density:Higher density: muchmuchfaster star formationfaster star formationuses up all the gasuses up all the gas––Nothing left to make aNothing left to make adiskdiskoror2.2.Lower spinLower spin––Gas used up beforeGas used up beforeangular momentum tookangular momentum tookoverover••Now we see a Now we see a spheresphereof old starsof old starsOr perhaps a different scenarioOr perhaps a different scenario……..••Spiral galaxy collisionsSpiral galaxy collisionsdestroy disks,destroy disks, leaveleavebehind behind ellipticalelliptical••Burst of star formationBurst of star formationuses up all the gasuses up all the gas••Leftovers:Leftovers: train wrecktrain wreck••EllipticalsEllipticals more commonmore commonin dense galaxy clustersin dense galaxy clusters(centers of clusters(centers of clusterscontaincontain central dominantcentral dominantgalaxiesgalaxies))NGC 4038/39 AntennaeNGC 4038/39 AntennaeWhy are Why are collisions betweencollisions betweengalaxiesgalaxies more likely than more likely thanbetween stars within a galaxy?between stars within a galaxy?A.A.Galaxies are much larger than starsGalaxies are much larger than starsB.B.Galaxies travel through space much fasterGalaxies travel through space much fasterthan starsthan starsC.C.Relative to their sizes, galaxies are closerRelative to their sizes, galaxies are closertogether than starstogether than starsD.D.Galaxies have higher Galaxies have higher redshifts redshifts than starsthan starsClicker QuestionClicker QuestionWhy are Why are collisions betweencollisions betweengalaxiesgalaxies more likely than more likely thanbetween stars within a galaxy?between stars within a galaxy?A.A.Galaxies are much larger than starsGalaxies are much larger than starsB.B.Galaxies travel through space much fasterGalaxies travel through space much fasterthan starsthan starsC.C.Relative to their sizes, galaxies are closerRelative to their sizes, galaxies are closertogether than starstogether than starsD.D.Galaxies have higher Galaxies have higher redshifts redshifts than starsthan starsClicker QuestionClicker QuestionColliding galaxies Colliding galaxies –– ““The AntennaeThe Antennae””HST detail: NGC 4038/39HST detail: NGC 4038/39Colliding Galaxies:Colliding Galaxies: NGC 4676NGC 4676““MiceMice”” with HST Advanced Camera for Surveys with HST Advanced Camera for SurveysStephanStephan’’s Quintet in HST details Quintet in HST detailMany Many interactinginteractinggalaxygalaxy systems systemsA mature example:A mature example:Elliptical shapeElliptical shape but with dust lanes? but with dust lanes?It may happen to us in future!It may happen to us in future!Andromeda (M31) in futureAndromeda (M31) in futureMessages From Messages From Galaxy InteractionsGalaxy Interactions1.1.In In dense clustersdense clusters,, galaxy collisionsgalaxy collisions (grazing(grazingor even head-on) must have beenor even head-on) must have been commoncommon2.2.WithWith successive passages,successive passages, spiral galaxiesspiral galaxiescan can tumble togethertumble together to form a to form a big ellipticalbig elliptical3.3.Vastly Vastly increased star birthincreased star birth from shocking from shockingthe gas and dustthe gas and dust (starburst galaxies;(starburst galaxies;coming up next!)coming up next!)4.4.Start Start rapid feedingrapid feeding of of supermassive supermassive blackblackholehole