ASTR 1120ASTR 1120General Astronomy:General Astronomy:Stars & GalaxiesStars & Galaxies!NNOUNCEMENTS!NNOUNCEMENTSHOMEWORK # 6 due Tue. Nov.3How Did Our Galaxy Form?How Did Our Galaxy Form?REVIEWOur galaxy probably formed from a giant gas cloudOur galaxy probably formed from a giant gas cloudREVIEWHalo stars formed first as gravity caused cloud to contractHalo stars formed first as gravity caused cloud to contractREVIEWStars continuously form in disk as galaxy grows older -Stars continuously form in disk as galaxy grows older - stars remain in disk plane stars remain in disk planeREVIEWDetailed studies: Halo stars formed in clumps that laterDetailed studies: Halo stars formed in clumps that latermergedmergedREVIEWGalactic Creation SummaryGalactic Creation Summary••What clues to our galaxyWhat clues to our galaxy’’s history dos history dohalo stars hold?halo stars hold?– Halo stars are all old, with a smallerproportion of heavy elements than diskstars, indicating that the halo formed first••How did our galaxy form?How did our galaxy form?– Our galaxy formed from a few hugeclouds of gas, with the halo stars formingfirst and the disk stars forming later, afterthe gas settled into a spinning diskREVIEWMeasuringMeasuring MassMass Using Using Orbital VelocitiesOrbital Velocitiessolar systemsolar systemRotation curve: orbital speedRotation curve: orbital speedvsvs..distance from the centerdistance from the center! v2=GMrrExpectation for the Milky WayExpectation for the Milky Way• There are a lot of starsin the center but alsosome outside• Rotation curve shouldincrease at first andthen fall although moreslowly than for solarsystemReality for the Milky WayReality for the Milky Way••Rotation curve is flatRotation curve is flator even rising!or even rising!••Most of the mass ofMost of the mass ofthe galaxy is outsidethe galaxy is outsidethe solar circle!the solar circle!••But few stars, littleBut few stars, littlegas theregas there……••DARK MATTERDARK MATTER ! ! probably in largeprobably in largehalo -- outweighshalo -- outweighsstars+gas by factorstars+gas by factor of 3 to 10 of 3 to 10Role of dark matter on rotation profileRole of dark matter on rotation profileDARK MATTERDARK MATTERDark matter halo for galaxiesDark matter halo for galaxies••Dark matter extendsDark matter extendsbeyond visible part ofbeyond visible part ofthe galaxythe galaxy -- mass is-- mass is~10x~10x stars and gas!stars and gas!••Probably not normalProbably not normalmass that we know ofmass that we know of(protons, neutrons,(protons, neutrons,electrons).electrons).••Most likely subatomicMost likely subatomicparticles, as yetparticles, as yetunidentifiedunidentified (weakly(weaklyinteracting massiveinteracting massiveparticles particles –– WIMPsWIMPs?)?)Journey to theJourney to the CenterCenterof the Galaxyof the Galaxy~.1 lySgr A*Infrared light from centerInfrared light from centerRadio emission from centerRadio emission from center1000 ly of the MW centerRadio emission from centerRadio emission from centerSwirling gas near centerSwirling gas near centerSwirling gas near centerSwirling gas near centerOrbiting stars near centerOrbiting stars near center1 Light-yearA Case for a A Case for a Supermassive Supermassive BlackBlackHole at the Galactic CenterHole at the Galactic Center• Doppler shiftmeasurementsof spiraling stars andgas suggest 3million MSun blackhole• Still too far out toexclude otherpossibilities…We need to be able to see closer in to reallyproveprove there is a supermasive black hole!Distance from Sgr A* (pc)Enclosed mass (Mo)Genzel 1996For Best Results: Use the WorldFor Best Results: Use the World’’ssLARGEST Infrared TelescopeLARGEST Infrared TelescopeThe Keck Telescopes on the Big Island of HawaiiStars appear to beorbiting somethingmassive butinvisible … aablack holeblack hole!Orbits of starsindicate a mass ofabout 3-4 million4 millionMMsun sun withinwithin 600600RRSchwarzchildSchwarzchildWe Know Exactly Where Sgr A*We Know Exactly Where Sgr A*Is and How Much it Weighs, butIs and How Much it Weighs, butWhat Does it What Does it ‘‘LOOKLOOK’’ Like? Like?X-ray flaresX-ray flaresfrom from Sgr Sgr A*A*suggest thatsuggest thattidal forces oftidal forces ofthe suspectedthe suspectedblack holeblack holeoccasionally occasionally teartearapart chunks ofapart chunks ofmattermatter about to about tofall infall inInfrared ObservationsInfrared Observations ShowedShowedthe Samethe Same TypesTypes of Flaresof FlaresState of AffairsState of Affairs atat the Galacticthe GalacticCenterCenter• Stellar orbits have made our Galaxy one of thebest proofs of supermassive black holes at thecenter of most galaxies.– Millions to billions of times the mass of our Sun.Must be created by something entirely differentthan a massive star supernova.• Flares are often observed in X-rays and IR– Observations of occasional flares are interpreted asthe result of occasional “swallowing” of a gas clumpor a star by the giant black hole.SUMMARY/Questions?SUMMARY/Questions?• What components make upour Galaxy?– Disk: mostly flat orbits,population I stars– Bulge & Halo: spheroidal orbits,Population II stars• How did our Galaxy form?– Several VERY massive cloudscolliding• What goes on in the Galaxy?– Star-Gas-Star recycling• What is most of the Galaxymass made of?– Dark Matter• What lives at the MW Center?– Sgr A*: Supermassive Black HoleChapter 20: GalaxiesChapter 20: GalaxiesAnd the Foundation of Modern CosmologyAnd the Foundation of Modern CosmologyWhat Are The Three MajorWhat Are The Three MajorTypes of Galaxies?Types of Galaxies?HubbleUltraDeepFieldHubbleUltraDeepFieldHubbleUltraDeepFieldSpiral GalaxyHubbleUltraDeepFieldSpiral GalaxyElliptical GalaxyHubbleUltraDeepFieldElliptical GalaxySpiral GalaxyHubbleUltraDeepFieldSpiral GalaxyElliptical GalaxyElliptical GalaxyIrregular GalaxiesHubbleUltraDeepFieldSpiral GalaxyElliptical GalaxyElliptical GalaxySpiralsSpirals~80% of galaxies~80% of galaxies••DisksDisks (with spiral(with spiralarms)arms) ++••SpheroidsSpheroids(bulges+halos)(bulges+halos)NGC 4414NGC 4414M100M100centercenterM101M101Barred SpiralBarred Spiralgalaxiesgalaxies•• Spiral arms emergeSpiral arms emerge from from central barcentral barNGC 1300NGC 1300NGC 1365NGC 1365HST: Center of barred spiral NGC 1365HST: Center of barred spiral NGC 1365IR viewIR