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

Prof. Prof. JuriJuri ToomreToomre TA: Nicholas NelsonTA: Nicholas NelsonLecture 21 Tues 29 Mar 2011Lecture 21 Tues 29 Mar 2011

zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomre

Tour of GalaxiesTour of Galaxies

•• Role of dustRole of dust in absorbing/scattering lightin absorbing/scattering light•• How can we How can we map the spiral arm structuremap the spiral arm structure of our of our

Milky Way galaxy?Milky Way galaxy?•• Next turn to mysterious Next turn to mysterious galactic centergalactic center in Milky in Milky

Way: Way: supermassivesupermassive black holeblack hole•• Hubble using Hubble using CepheidsCepheids showed showed AndromedaAndromeda is a is a

distinct distinct ““island universeisland universe”” –– another Galaxy !another Galaxy !•• ReadRead 20.120.1 Galaxy Types,Galaxy Types, and for Thurs lectureand for Thurs lecture

20.220.2 Measuring Cosmic Distances Measuring Cosmic Distances and and 20.3 20.3 HubbleHubble’’s Laws Law

TodayToday

•• New Homework Set # 9 passed out: New Homework Set # 9 passed out: Hubble Law Hubble Law + Distances+ Distances HW # 8.5 due in classHW # 8.5 due in class

•• Observatory Night # 6 Observatory Night # 6 tonighttonight (Tues March 29) (Tues March 29) 8:30pm+ (signup)8:30pm+ (signup)

Crib Sheet AwardsCrib Sheet Awards

Psychic Powers Award Psychic Powers Award

International Collaboration AwardInternational Collaboration Award

Tyler BlankenshipTyler Blankenship

Stacey Stacey RugenskiRugenski

Review:Review:OneOne--page story page story

Cartoon sketchCartoon sketchof Milky Wayof Milky Way

EdgeEdge--onon

TopTop

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Inventory ofInventory of““stuffstuff”” makingmakingup our galaxyup our galaxy

Stars Stars

Gas Gas

DustDust+ + ““darkdarkmattermatter””

REMINDERREMINDER

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O & B starO & B starassociationsassociations

many cluster starsmany cluster starsjoin to blowjoin to blow““big bubblesbig bubbles””

TrifidTrifid emission nebula emission nebula ““O & B star associationsO & B star associations””

visiblevisible Spitzer infraredSpitzer infrared

Clicker Clicker –– stars and stars and ““heavy metalsheavy metals””

•• The ages of stars suggest that the bulge The ages of stars suggest that the bulge and halo of the Milky Way formed before and halo of the Milky Way formed before many of the stars in the disk. Which would many of the stars in the disk. Which would you expect to have you expect to have more heavy metalsmore heavy metals(higher (higher metallicitymetallicity)?)?

•• A.A. Halo and bulge starsHalo and bulge stars

•• B.B. Disk starsDisk stars

•• C.C. No differenceNo difference

B.B.

•• B.B. Disk starsDisk stars are are continually forming out of continually forming out of gas that is more and gas that is more and more more ““pollutedpolluted”” by heavy by heavy metals.metals.

•• The The OLD globular OLD globular clustersclusters in the haloin the halo were were formed a long time ago formed a long time ago before the galaxy was so before the galaxy was so polluted polluted –– they have very they have very low low ““metallicitiesmetallicities””

ISM:ISM:

A little A little DUSTDUSTgoes a longgoes a longway!way!

““ReddensReddens””the lightthe light

AbsorbsAbsorbsthe lightthe light

SEMISEMI--WARMWARM stuff: stuff: dustdust

•• DUST:DUST: absorbsabsorbsvisible and UV lightvisible and UV light

•• TransparentTransparent to to long wavelengthslong wavelengths(red, IR, radio)(red, IR, radio)

•• Emits IR lightEmits IR light

HorseheadHorsehead NebulaNebula

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Dust+darkDust+darkmolecularmolecularcloudsclouds

HorseheadHorseheadin closein close--upup

VLTVLT

EagleEagleNebulaNebula

Clouds + dust Clouds + dust in Eagle Nebulain Eagle Nebula

RosettaRosettaNebulaNebulaO & B starO & B starcarving +carving +dust filamentsdust filaments

WidefieldWidefieldInfraredInfraredSurveySurveyExplorerExplorer(WISE)(WISE)

NGC 3603NGC 3603

Dark and dusty stellar nurseriesDark and dusty stellar nurseries

NebulaNebulaRCW 49RCW 49Stellar jewelsStellar jewelsSpitzer IRSpitzer IR

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The Star-Gas-Star Cycle

Disk is busy!Disk is busy!

Cycle ofCycle ofstarsstars gas gas starsstars

Complex cycleComplex cycleis ongoing is ongoing ……..

Globular clusters onGlobular clusters onCOBE IR sky imageCOBE IR sky image

ShapleyShapley’’ss (1920) (1920) distances to distances to globular clusters:globular clusters:Sun at 18 Sun at 18 kpckpc fromfromcenter (twice too far!)center (twice too far!)

WHERE are we in MW?WHERE are we in MW?

DustDust makes it makes it hard to hard to estimate distancesestimate distances(stars dimmed)(stars dimmed)

SUNSUNXX

Clicker Clicker –– galaxy centergalaxy center

•• We want to map out the structure of the We want to map out the structure of the central central corecore of the Milky Way. What of the Milky Way. What wavelength wavelength should we be using, and why?should we be using, and why?

•• A.A. IR or radioIR or radio

•• B.B. visible lightvisible light

•• C.C. XX--raysrays

A.A.

COLDCOLD stuff: dark cloudsstuff: dark clouds

•• Molecular CLOUDSMolecular CLOUDS

•• Dark, dusty, cold Dark, dusty, cold ((10 10 -- 30 K30 K))

•• Emit Emit molecular molecular emission linesemission lines in far in far IR, radio IR, radio

•• Orion imageOrion image here in here in carbon monoxidecarbon monoxide(CO) (CO) ---- colors are colors are Doppler shiftsDoppler shifts

COCODopplerDopplerImagesImages

COLDCOLD hydrogen throughouthydrogen throughout

•• Even the coldest Even the coldest hydrogen emits hydrogen emits faint emission line faint emission line in the in the RADIORADIO

•• Wavelength 21 cmWavelength 21 cm

•• Emission from Emission from flip of flip of electronelectron from from spinupspinup to to spindownspindown statestate

All sky 21 cm radio mappingAll sky 21 cm radio mapping

Q:Q: Just HOW do weJust HOW do weknowknow that that MW hasMW hasspiral structure?spiral structure?

A:A: Radio astronomersRadio astronomerscould map it withcould map it with2121--cm line of hydrogencm line of hydrogen

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21 cm21 cmemissionemission(radio)(radio)

SamplingSamplingneutral hydrogenneutral hydrogenatoms (cold)atoms (cold)

also how MRIalso how MRIdoes it in medicaldoes it in medicalimaging!imaging!

Green Bank 100 m Radio TelescopeGreen Bank 100 m Radio Telescope VAVA

VLBA Radio Telescope VLBA Radio Telescope Owens ValleyOwens Valley

VLA VLA -- SicorroSicorro

Very Large Array (VLA)Very Large Array (VLA) Socorro NMSocorro NM

Radio mappingRadio mappingcool H cloudscool H cloudsin MW diskin MW disk

Doppler shiftedDoppler shiftedradio emissionradio emission

SUNSUN oo

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Another viewAnother viewof 21 cm radioof 21 cm radiomappingmapping

SUNSUN

Beam cuts acrossBeam cuts acrossdifferent spiral armsdifferent spiral arms

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Radio mapRadio map (21 cm) of spiral structure in MW (21 cm) of spiral structure in MW

Ragged spiralRagged spiralstructure revealedstructure revealed

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SUNSUN

GALAXYGALAXYCENTERCENTER

Emitted radio Emitted radio waves can waves can penetrate through penetrate through gas and dustgas and dust

CloseClose--up viewup viewof our vicinityof our vicinity

towardtowardgalactic centergalactic center

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““Orion Orion armarm””

Center of our galaxyCenter of our galaxy

Located in direction of Located in direction of SagittariusSagittarius

•• Dust obscures our Dust obscures our visionvision of much of the of much of the galaxy in visible and galaxy in visible and UV light.UV light.

•• XX--rays only highlight rays only highlight the hottest and the hottest and weirdest placesweirdest places

•• IR and radio lightIR and radio lightpass through pass through unaffected, show unaffected, show dust, stars, gasdust, stars, gas

MW centerMW center3939’’ boxbox

Unusual activityUnusual activityat galaxy centerat galaxy center

Galactic center:Galactic center: IR reveals a dense star clusterIR reveals a dense star cluster

IR 1IR 1

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RadioRadiomappingmappingof galacticof galacticcentercenter

Zooming in on Zooming in on Sagittarius A*Sagittarius A*

Radio 2Radio 2

Radio 3Radio 3

Radio 4Radio 4

IR 5IR 5

SgrSgr A*A*

VLTVLTIR+AOIR+AO

VLT in IR + adaptive opticsVLT in IR + adaptive opticsSgrSgr A* A* orbits orbits

Star motionStar motionaround around black hole black hole at galacticat galacticcentercenter

VLT: IR+AOVLT: IR+AO

SgrSgr A*A*orbitsorbits

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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