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ASTR 1040 ASTR 1040 AccelAccel AstroAstro:: Stars & GalaxiesStars & Galaxies

Prof. Prof. JuriJuri ToomreToomre TA: Nicholas NelsonTA: Nicholas Nelson

Lecture 22 Lecture 22 ThurThur 31 March 201131 March 2011zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomre

NGC 1232NGC 1232Spiral Spiral SbSb

On TodayOn Today’’s Radars Radar

•• Revisit Revisit SupermassiveSupermassive Black HoleBlack Hole in 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 to Galaxies (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 5 meets 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)

SgrSgr A*A*

VLTVLTIR+AOIR+AO

REVISITREVISIT

Star motionStar motionaround around black hole black hole at galacticat galacticcentercenter

VLT: IR+AOVLT: IR+AO

SgrSgr A*A*orbitsorbits

Rotation velocity at galaxy centerRotation velocity at galaxy center

Black holeBlack hole still less than 1/1000 of MW massstill less than 1/1000 of MW mass

Some 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 HOLE

But further 20%But further 20%uncertainty fromuncertainty fromdistance determinationdistance determination

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Sag A*Sag A*in Chandrain ChandraXX--ray viewray view

ExhibitsExhibitsoutbursts,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’’ss supermassivesupermassive black 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 telescopes

D.D.

Measuring galactic distancesMeasuring galactic distances

Edwin HubbleEdwin Hubble mademadebreakthrough usingbreakthrough usingCepheid variables Cepheid variables to measure distanceto measure distance

Found AndromedaFound Andromedafar outsidefar outside Milky WayMilky Way

Huge step forward inHuge step forward inthinking about universethinking about universe NGC 4414NGC 4414

HOW DID IT ALL BEGIN?HOW DID IT ALL BEGIN?

Cepheid variableCepheid variablestarsstars as distanceas distanceindicators:indicators:““standard candlestandard candle””

Vital discovery byVital discovery byHenrietta Leavitt (1912)Henrietta Leavitt (1912)

Cepheid starsCepheid stars in 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)

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Cepheid variable Cepheid variable starsstars

brighter brighter CepheidsCepheidshave longer periodshave longer periods

Period Period --LuminosityLuminosityrelationrelation

AndromedaAndromeda found to be far found to be far outsideoutside Milky Way Milky Way –– another another ““island universeisland universe”” : galaxy!: galaxy!

•• Edwin Hubble Edwin Hubble in 1924 in 1924 identified identified CepheidsCepheids in 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 Wilson

Begins new era in 1924 !Begins new era in 1924 !

Edwin Hubble Edwin Hubble in 1924 in 1924 identified identified CepheidsCepheids in in Andromeda (M31) Andromeda (M31) showed they were far showed they were far outside of Milky Way! outside of Milky Way!

AndromedaAndromeda found to be far found to be far outsideoutside Milky 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. Wilson

Andromeda 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 lyly away 260,000 away 260,000 lyly in diameterin diameter

NGC205NGC205

M32M32

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Andromeda surprises with Spitzer in IRAndromeda surprises with Spitzer in IR

M32M32

NGC205NGC205

3.6 microns (blue), 4.5 (green)3.6 microns (blue), 4.5 (green) 8 microns (red)8 microns (red)

M31M31

M31: 11,000 image composite with SpitzerM31: 11,000 image composite with Spitzer

1 1 Striking rings of dust and Striking rings of dust and starbirthstarbirth22 Ring splits into two, forming hole on lower rightRing splits into two, forming hole on lower right3 3 Delicate tracings of spiral arms into very centerDelicate tracings of spiral arms into very center

M31: Forensic evidence of galactic collisionM31: Forensic evidence of galactic collision

M32 plunged through disk on polar axis ~210 My ago ??M32 plunged through disk on polar axis ~210 My ago ??

M31: Beautiful neighbor in UV and IRM31: Beautiful neighbor in UV and IR

GALEX:GALEX: FarFar--UV (blue) UV (blue) –– young hot massive stars young hot massive stars NearNear--UV (green) UV (green) –– relatively older starsrelatively older stars

SPITZER:SPITZER: 24 micron IR (red) 24 micron IR (red) –– cool, dusty star formingcool, dusty star forming

M31 M31 from from WISEWISE + M32 (below) + M110 + M32 (below) + M110 (NGC 205)(NGC 205)

LATEST IR IMAGINGLATEST IR IMAGING

HubbleHubble’’ssscheme toscheme tolabel galaxieslabel galaxies

ellipticalsellipticals EE

spirals Sspirals S

barred spirals SBbarred spirals SB

lenticularlenticular

+ some + some ““irregularsirregulars””

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Barred spiralBarred spiralgalaxiesgalaxies

•• Spiral arms emergeSpiral arms emergefrom from central barcentral bar

NGC 1300NGC 1300

NGC 1365NGC 1365

““Tuning forkTuning fork”” shown with shown with mugshotsmugshots of galaxiesof galaxies

spiralsspirals--barredbarred

spiralsspirals

ellipticalsellipticals

M101M101

SpiralsSpirals~80% of galaxies~80% of galaxies•• DisksDisks (with spiral (with spiral

arms) +arms) +

•• SpheroidsSpheroids((bulges+halosbulges+halos))

NGC 4414NGC 4414

M100M100centercenter

HST: Center of barred spiral NGC 1365HST: Center of barred spiral NGC 1365

IR viewIR view

LenticularsLenticulars(lens(lens--shaped)shaped)

•• Disks, but less gas Disks, but less gas and star formationand star formation

•• Note lack of dust & Note lack of dust & pink nebulaepink nebulae

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EllipticalsEllipticals~15% of galaxies~15% of galaxies

•• Round or slightly Round or slightly flattenedflattened

•• Very littleVery little cold gas, cold gas, dust, or young starsdust, or young stars

•• Reddish color = old Reddish color = old stars (red giants, red stars (red giants, red main sequence)main sequence)

Dwarf Dwarf ellipticalsellipticals

•• Most common type of Most common type of galaxy?galaxy?

•• Only know nearby Only know nearby ones (since faint !)ones (since faint !)

NGC 205 NGC 205 2MASS2MASS

IrregularsIrregulars•• Galaxies in Galaxies in

transformation?transformation?Often LOTS of Often LOTS of star birth star birth

M82M82

NGC 674NGC 674

•• SpiralsSpirals –– mostly mostly in groups (3in groups (3--10 10 galaxies)galaxies)

Where do spirals and Where do spirals and ellipticalsellipticals live?live?

HST: HST: HicksonHickson CG 87CG 87

•• EllipticalsEllipticals --most often in most often in dense clusters dense clusters of galaxiesof galaxies(involve 100(involve 100’’s s to 1000to 1000’’s)s)

HST: HST: AbellAbell 16891689

The Big PictureThe Big Picture:: Universe is Universe is filledfilled with with network of galaxies in groups and clustersnetwork of galaxies in groups and clusters

~100 billion galaxies!~100 billion galaxies!

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Pattern of galaxiesPattern of galaxies (3 million+),15(3 million+),15oo portion of skyportion of sky

Brighter =Brighter =more galaxiesmore galaxies

Clicker Clicker –– reading aheadreading ahead

•• What are the What are the MagellanicMagellanic CloudsClouds??

•• A.A. Two nebulae in disk of Milky Way visible Two nebulae in disk of Milky Way visible only in southern hemisphereonly in southern hemisphere

•• B.B. Clouds of dust and gas in many places Clouds of dust and gas in many places throughout the Milky Way galaxythroughout the Milky Way galaxy

•• C.C. Two small galaxies that orbit Milky WayTwo small galaxies that orbit Milky Way

•• D.D. StarStar--forming clouds in constellation Orionforming clouds in constellation Orion

C.C.

Our Our ““local grouplocal group””of galaxiesof galaxies

3 spirals:3 spirals:Andromeda (M31)Andromeda (M31)Milky WayMilky WayTriangulumTriangulum (M33)(M33)2 irregulars:2 irregulars:LMCLMCSMCSMC16+ dwarfs16+ dwarfs