1ASTR 1040 ASTR 1040 AccelAccelAstroAstro::Stars & GalaxiesStars & GalaxiesProf. Prof. JuriJuriToomreToomreTA: Nicholas NelsonTA: Nicholas NelsonLecture 22 Lecture 22 ThurThur31 March 201131 March 2011zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomreNGC 1232NGC 1232Spiral Spiral SbSbOn TodayOn Today’’s Radars Radar••Revisit Revisit SupermassiveSupermassiveBlack HoleBlack Holein Milky Wayin Milky Way••Edwin Hubble shows: Edwin Hubble shows: Andromeda is a distinct galaxy Andromeda is a distinct galaxy using using Cepheid Variable StarsCepheid Variable Stars••Today turn toToday turn toGalaxies (Chap 20) Galaxies (Chap 20) starting with Hubblestarting with Hubble’’s s scheme to classify spiral galaxies, scheme to classify spiral galaxies, ellipticalsellipticals, and irregulars , and irregulars ••Then look at the challenge of Then look at the challenge of measuring big distances measuring big distances to to figure out how far away things are in universe figure out how far away things are in universe ––leads to leads to HubbleHubble’’s law of expansions law of expansion••ReRe--read read 20.3 Hubble20.3 Hubble’’s Law (Measuring Cosmic Evolution)s Law (Measuring Cosmic Evolution)carefully carefully ••Next class on Next class on Tues April 5Tues April 5meets in Fiske Planetarium, to meets in Fiske Planetarium, to see see Birth of Stars and Planets Birth of Stars and Planets (review Chap 16 (review Chap 16 beforehand)beforehand)SgrSgrA*A*VLTVLTIR+AOIR+AOREVISITREVISITStar motionStar motionaround around black hole black hole at galacticat galacticcentercenterVLT: IR+AOVLT: IR+AOSgrSgrA*A*orbitsorbitsRotation velocity at galaxy centerRotation velocity at galaxy centerBlack holeBlack holestill less than 1/1000 of MW massstill less than 1/1000 of MW massSome of central mass Some of central mass is stars, joined by is stars, joined by 3.7 +/3.7 +/--0.2 million 0.2 million solar masssolar massBLACK HOLEBLACK HOLEBut further 20%But further 20%uncertainty fromuncertainty fromdistance determinationdistance determination2Sag A*Sag A*in Chandrain ChandraXX--ray viewray viewExhibitsExhibitsoutbursts,outbursts,but starvedbut starvedof fuel ?of fuel ?QuestionQuestion::Why no powerful jet and accretion Why no powerful jet and accretion disk near disk near MWMW’’sssupermassivesupermassiveblack hole?black hole?••Why not much Why not much emission in emission in XX--rays ? rays ? …….though .though other signs of other signs of activityactivity••AnswerAnswer: : maybe it hasmaybe it haseaten all it caneaten all it can––at least for at least for now ?now ?LargeLarge--scale structure in Milky Wayscale structure in Milky Way••We can observe the atomic hydrogen in We can observe the atomic hydrogen in interstellar gas in Milky Way with _______.interstellar gas in Milky Way with _______.••A.A.spacespace--based ultraviolet telescopesbased ultraviolet telescopes••B.B.xx--ray telescopesray telescopes••C.C.groundground--based visible light telescopes based visible light telescopes ••D.D.21 cm observations by radio telescopes21 cm observations by radio telescopesD.D.Measuring galactic distancesMeasuring galactic distancesEdwin HubbleEdwin Hubblemademadebreakthrough usingbreakthrough usingCepheid variables Cepheid variables to measure distanceto measure distanceFound AndromedaFound Andromedafar outsidefar outsideMilky WayMilky WayHuge step forward inHuge step forward inthinking about universethinking about universeNGC 4414NGC 4414HOW DID IT ALL BEGIN?HOW DID IT ALL BEGIN?Cepheid variableCepheid variablestarsstarsas distanceas distanceindicators:indicators:““standard candlestandard candle””Vital discovery byVital discovery byHenrietta Leavitt (1912)Henrietta Leavitt (1912)Cepheid starsCepheid starsin Hin H--R diagramR diagram••““Instability stripInstability strip””----region in Hregion in H--R diagram R diagram with large, bright starswith large, bright stars••Outer regions of star are Outer regions of star are unstable and tend to unstable and tend to pulsatepulsate••Star expands and Star expands and contractscontracts,,getting brighter getting brighter and fainterand fainterReminderReminder(Fig 15.14)(Fig 15.14)3Cepheid variable Cepheid variable starsstarsbrighter brighter CepheidsCepheidshave longer periodshave longer periodsPeriod Period --LuminosityLuminosityrelationrelationAndromedaAndromedafound to be far found to be far outsideoutsideMilky Way Milky Way ––another another ““island universeisland universe””: galaxy!: galaxy!••Edwin Hubble Edwin Hubble in 1924 in 1924 identified identified CepheidsCepheidsin in Andromeda (M31) Andromeda (M31) showed they were far showed they were far outside of Milky Way! outside of Milky Way! ••Now known Now known distancedistance: : 2.3 million 2.3 million lyly••His first big discovery His first big discovery (more to come) (more to come) ……Hubble using new Hubble using new 100100””Hooker telescopeHooker telescopeat Mt. Wilson (above LA)at Mt. Wilson (above LA)100100””Hooker telescope at Mt WilsonHooker telescope at Mt WilsonBegins new era in 1924 !Begins new era in 1924 !Edwin Hubble Edwin Hubble in 1924 in 1924 identified identified CepheidsCepheidsin in Andromeda (M31) Andromeda (M31) showed they were far showed they were far outside of Milky Way! outside of Milky Way! AndromedaAndromedafound to be far found to be far outsideoutsideMilky Way Milky Way ––another another ““island universeisland universe””: galaxy!: galaxy!Hubble (and Jeans) at new 100Hubble (and Jeans) at new 100””Hooker telescope on Mt. WilsonHooker telescope on Mt. WilsonAndromeda Andromeda ––M31 (M31 (SbSb))First galaxy shown First galaxy shown by Hubble (1924)by Hubble (1924)to be a distinctto be a distinct““island universeisland universe””2.5 million 2.5 million lylyaway 260,000 away 260,000 lylyin diameterin diameterNGC205NGC205M32M324Andromeda surprises with Spitzer in IRAndromeda surprises with Spitzer in IRM32M32NGC205NGC2053.6 microns (blue), 4.5 (green)3.6 microns (blue), 4.5 (green)8 microns (red)8 microns (red)M31M31M31: 11,000 image composite with SpitzerM31: 11,000 image composite with Spitzer1 1 Striking rings of dust and Striking rings of dust and starbirthstarbirth22Ring splits into two, forming hole on lower rightRing splits into two, forming hole on lower right3 3 Delicate