1ASTR 1040 ASTR 1040 AccelAccelAstroAstro::Stars & GalaxiesStars & GalaxiesProf. Prof. JuriJuriToomreToomreTA: Nicholas NelsonTA: Nicholas NelsonLecture 24 Lecture 24 ThurThur7 Apr 20117 Apr 2011zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomreStefanStefan’’ssQuintetQuintetOn Galaxy Evolution LaneOn Galaxy Evolution Lane••Look at our local group of galaxiesLook at our local group of galaxies••Challenge of Challenge of measuring distances in universemeasuring distances in universe••Most striking:Most striking:many galaxies experience many galaxies experience collisionscollisionsthus becoming thus becoming ““interacting galaxiesinteracting galaxies””••Begin to discuss Begin to discuss active galaxies active galaxies andandquasarsquasars••ReRe--readread21.3 Quasars and active galactic nuclei21.3 Quasars and active galactic nucleiin detailin detailOur Our ““local grouplocal group””of galaxiesof galaxies3 spirals:3 spirals:Andromeda (M31)Andromeda (M31)Milky WayMilky WayTriangulumTriangulum(M33)(M33)2 irregulars:2 irregulars:LMCLMCSMCSMC16+ dwarfs16+ dwarfsBiggest is Biggest is AndromedaAndromeda((SbSb--M31)M31)••Andromeda is Andromeda is ~2.5 million light ~2.5 million light years away (or ~30 years away (or ~30 MW diameters), has MW diameters), has ~1.5 mass of MW ~1.5 mass of MW ••We see her as We see her as ““sheshe””was 2.5 million years was 2.5 million years ago, not as she is ago, not as she is today! today! ––this is this is lookbacklookbacktimetime••Oops! she may crash Oops! she may crash into MW in about 2 into MW in about 2 billion yearsbillion yearsTriangulumTriangulum(M33)(M33)••1/5 mass of MW, 1/5 mass of MW, spiral classified as spiral classified as ScSc••Several bright (pink) Several bright (pink) star forming regionsstar forming regionsLarge & Small Large & Small MagellanicMagellanicCloudsCloudsLMCLMCSMCSMC2LMC has 30 LMC has 30 DoradusDoradus, home , home of SN 1987Aof SN 1987ASN 1987a SN 1987a ––before and afterbefore and afterClicker Clicker ----reading on galaxiesreading on galaxies••How might you classify this galaxy?How might you classify this galaxy?••A.A.SaSa••B.B.SBbSBb••C.C.EE••D.D.SOSOB.B.Hubble: Hubble: nextnextshowed universe showed universe appeared to be appeared to be expandingexpanding!!••VestoVestoSlipherSlipher(1912) reported that most (1912) reported that most galaxies showed Doppler galaxies showed Doppler redshiftsredshifts••Edwin HubbleEdwin Hubble, using new 100, using new 100””telescope, telescope, started busily measuring galaxy started busily measuring galaxy redshiftsredshifts••HubbleHubble(1929) announced that (1929) announced that redshiftsredshiftsof of galaxiesgalaxiesappear to appear to increase with distanceincrease with distancefrom usfrom us••This was startling: suggests an This was startling: suggests an EXPANDING UNIVERSEEXPANDING UNIVERSE!!Hubble andHubble andrecession ofrecession ofgalaxiesgalaxies: : measuredmeasuredmany many redshiftsredshiftsFurther away,Further away,greater greater redshiftredshift!!Hubble Hubble guessedguessedtheir distancestheir distancesbybysize and brightnesssize and brightness----underestimatedunderestimatedby factor 10!by factor 10!““HubbleHubble’’s Laws Law””HubbleHubble’’s (1929) originals (1929) originalScatterScatterhere from here from randomrandomvelocitiesvelocitiesof nearby galaxies,of nearby galaxies,unreliable distance estimatesunreliable distance estimates3Best Best currentcurrentvalues forvalues forexpansionexpansionHHoo= = 7171+/+/--44km/km/s/Mpcs/MpcHubble (1929) plot extended only to 2 Hubble (1929) plot extended only to 2 MpcMpc, H, Hoowas ~500 !was ~500 !““HUBBLE CONSTANTHUBBLE CONSTANT””velocityvelocitydistancedistanceUniverse expandsUniverse expandslike raisin bread !like raisin bread !Balloon analogy for Balloon analogy for expanding universeexpanding universe••On an expanding On an expanding balloon, no galaxy balloon, no galaxy is at the is at the ““centercenter””of of expansion; no edgeexpansion; no edge••Expansion happens Expansion happens into a higher into a higher dimensiondimension(2(2--D D surface into a 3surface into a 3--D D space)space)••Is our 3Is our 3--D space D space expanding through expanding through a 4a 4ththdimension?dimension?Mapping the universe: need Mapping the universe: need distancesdistancesto galaxies!to galaxies!••Identify (and calibrate) properties of galaxies Identify (and calibrate) properties of galaxies that could serve as that could serve as ““STANDARD CANDLESSTANDARD CANDLES””----beyond direct measure by beyond direct measure by trigonometric parallaxtrigonometric parallax••1.1.Make some measure of an object which Make some measure of an object which identifies its identifies its luminosityluminosity(like (like periodperiodin Cepheid)in Cepheid)••2.2.Use this luminosity and measure apparent Use this luminosity and measure apparent brightness to brightness to infer distanceinfer distanceto itto itMainMain--Sequence FittingSequence Fitting••Start with cluster Start with cluster AA(upper)(upper)whose whose distance known via distance known via parallaxparallax••Compare with other Compare with other cluster cluster B B (lower)(lower)••Get Get distance to Bdistance to Bfrom brightness from brightness difference difference DISTANCEDISTANCEESTIMATE 1ESTIMATE 1AABBMM--S Fitting S Fitting ““pinned topinned to””nearby M45, nearby M45, Hyades Cluster,151 Hyades Cluster,151 lylyawayaway4Cepheid variable starsCepheid variable starsbrighter brighter CepheidsCepheidshave longer periodshave longer periodsPeriod Period --LuminosityLuminosityrelationrelationDISTANCEDISTANCEESTIMATE 2ESTIMATE 2CepheidsCepheidsvariables as variables as standard candlesstandard candles1. Measure 1. Measure periodperiodof variabilityof variability2. From period2. From period--luminosity luminosity relation, infer the relation, infer the luminosityluminosity3. Compare with 3. Compare with apparent apparent brightnessbrightnessand and thus determine thus determine distancedistanceCepheid variable in M100 (HST)Cepheid variable in M100 (HST)DISTANCEDISTANCEESTIMATE 2ESTIMATE 2Number of Number of FuzzierFuzzierDistance Distance EstimatorsEstimators••A.A.Apparent brightness of (resolved) red Apparent brightness of (resolved) red and