Post on 26-Jul-2020
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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
oo
oo
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
oo
Another viewAnother viewof 21 cm radioof 21 cm radiomappingmapping
SUNSUN
Beam cuts acrossBeam cuts acrossdifferent spiral armsdifferent spiral arms
oo
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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
xx
oo
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
oo
““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