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

Prof. Prof. JuriJuri ToomreToomre TAs: Ben Brown, Adam JensenTAs: Ben Brown, Adam JensenLecture 20 Lecture 20 ThurThur 23 Mar 0623 Mar 06zeus.colorado.edu/astr1040zeus.colorado.edu/astr1040--toomretoomre

EagleEagleNebulaNebula

Today in Our GalaxyToday in Our Galaxy•• Our Milky Way Galaxy Our Milky Way Galaxy in overview, seeing in overview, seeing

various components of any various components of any spiral galaxy spiral galaxy –– and a and a finefine SONGSONG

•• Consider why Consider why spiral patterns are made in the diskspiral patterns are made in the diskof galaxies, including our ownof galaxies, including our own

•• Examine the Examine the rotation curve rotation curve of our galaxy, and the of our galaxy, and the unseen mass unseen mass (dark matter) (dark matter) that it impliesthat it implies

•• Complete your reading ofComplete your reading of 19.219.2 StarStar--GasGas--Star Star Cycle, Cycle, provide discussion response by 3 Aprprovide discussion response by 3 Apr

•• Second MidSecond Mid--Term ExamTerm Exam returned today returned today •• Observatory Night 5Observatory Night 5 on on MonMon 3 Apr 8:30pm3 Apr 8:30pm

So did we really love this exam?So did we really love this exam?

RESULTS FROM SECOND MIDRESULTS FROM SECOND MID--TERM EXAMTERM EXAM

SECOND MIDSECOND MID--TERM EXAMTERM EXAM

•• Grade boundariesGrade boundaries, based on 150 points:, based on 150 points:

•• If 133/150 (89%) or over, If 133/150 (89%) or over, AA’’ss [45%][45%]•• 106/150 (71%) or over, 106/150 (71%) or over, BB’’ss [40%][40%]•• 95/150 (64%) or over, 95/150 (64%) or over, CC’’ss [15%][15%]Also +, plain, and Also +, plain, and –– within these rangeswithin these ranges

Go through answer sheetGo through answer sheet –– and talk to us if and talk to us if do not understand our choices. Keep exam do not understand our choices. Keep exam + answers for future review (comp final)+ answers for future review (comp final)

This award, for the crib sheet withThis award, for the crib sheet withThe Most Aesthetic AppealThe Most Aesthetic Appeal

Is presented toIs presented to

Becky Becky StudleyStudley

This award, for the crib sheet withThis award, for the crib sheet withThe Most Economical use of SpaceThe Most Economical use of Space

Is presented toIs presented to

Fabio Fabio MezzaliraMezzalira

Horray

Fabio!

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This award, for the crib sheet withThis award, for the crib sheet withThe Most Immaculate Scribing The Most Immaculate Scribing

Is presented toIs presented to

Cassandra MooreCassandra Moore

This award, for the crib sheet withThis award, for the crib sheet withTheThe MostMost UseUse ofof ColorColor

Is presented toIs presented to

PPhhiilliipp HHoollttzzmmaann

Now toNow to Our Milky Way GalaxyOur Milky Way Galaxy The Milky WayThe Milky Way (fuzzy ribbon of (fuzzy ribbon of light across the sky)light across the sky)

Size of Milky WaySize of Milky Way

•• 100100--400400 billionbillion starsstars•• 100,000 light years 100,000 light years

in in diameterdiameter, or, or~ 30,000 pc = ~ 30,000 pc = 30 30 KpcKpc

(kilo(kilo--parsecs)parsecs)

•• SunSun is located about is located about 8.5 8.5 kpckpc from center, from center, in the `Orion Armin the `Orion Arm’’

ArtistArtist’’s sketch!s sketch!

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If If wewe might see might see Milky WayMilky Way from outside from outside

Spiral Spiral SbSb galaxygalaxyNGC 4414NGC 4414

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Milky Way Anatomy: Spiral GalaxyMilky Way Anatomy: Spiral Galaxy

•• DiskDisk:: includes includes spiral armsspiral arms ----young, new star young, new star formationformation

•• Bulge & HaloBulge & Halo::older stars, older stars, globular clustersglobular clusters

Clicker Clicker –– Where are we?Where are we?•• Why was it so difficult to figure out Why was it so difficult to figure out where in the where in the

Milky WayMilky Way are the Sun and Earth located, and if are the Sun and Earth located, and if ours is the only ours is the only ““nebulanebula”” (galaxy) ?(galaxy) ?

•• A.A. We are immersed in a soup of stars, gas and dust, so hard to see far

•• B.B. In a middle of city of stars, hard to figure shape of overall `metropolitan area’

•• C.C. Gas and dust can absorb light, making distance estimates uncertain

•• D.D. All of the above

D.D.

Disk is very thin!Disk is very thin!

ArtistArtist’’s edges edge--on viewon view

Disk is very thin!Disk is very thin!

ArtistArtist’’s edges edge--on viewon view

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Spiral galaxy Spiral galaxy NGC 891NGC 891 –– nearly edgenearly edge--onon

stars, gas, dust in diskstars, gas, dust in disk

OneOne--pager:pager:ALL about us!ALL about us!

SketchSketchof Milky Wayof Milky Way Edge

Edge--onon

TopTop

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Stars and gas are all moving!Stars and gas are all moving!

THIS INSPIRES A SONG!THIS INSPIRES A SONG!

THE GALAXY THE GALAXY ----LIGHTEN UPLIGHTEN UP

Sing our way toSing our way tothe Milky Waythe Milky Way

PrePre--Milky Way: early halo + disk Milky Way: early halo + disk

How to build a How to build a spiral galaxyspiral galaxy

(or so we think!)(or so we think!)

The Star-Gas-Star Cycle

Cycle ofCycle ofstarstar gas gas

starstar

All spiral galaxiesAll spiral galaxiesare constantly changingare constantly changing

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

Stars Stars

Gas Gas

DustDust+ + ““darkdarkmattermatter””

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Many views of our galaxy diskMany views of our galaxy disk Reading clicker Reading clicker –– mapping our galaxymapping our galaxy

•• We want to map the We want to map the structures of very cold structures of very cold gas within the dusty diskgas within the dusty disk of the Milky Way. of the Milky Way. What wavelengths should we be using, What wavelengths should we be using, and why?and why?

•• A.A. radioradio•• B.B. visible lightvisible light•• C.C. xx--raysrays

A.A.

A.A. RadioRadio

•• DustDust obscuresobscures our our vision of much of the vision 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

•• 21 cm radio waves21 cm radio wavesmap normal hydrogen map normal hydrogen gas gas ---- these pass these pass through dust unaffectedthrough dust unaffected

confused visible imageconfused visible image

MW disk in radioMW disk in radio

Motion of stars in spiral galaxyMotion of stars in spiral galaxy

Disk:Disk:circular +circular +bit up/downbit up/down

Halo & bulge:Halo & bulge:swarming in swarming in and outand out

DifferentDifferentstar motionsstar motionsin disk & haloin disk & halo

1.1.

2.2.

MMRR = R = R xx V V 22 / G/ GStars moving in circles: orbital velocity lawStars moving in circles: orbital velocity law

massmassinwardinward

radiusradius orbitalorbitalvelocityvelocity

……faster orbit,faster orbit,more massmore mass

MW rotation curveMW rotation curve

solar systemsolar system

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Reality for the Milky WayReality for the Milky Way•• Rotation curve is flat Rotation curve is flat

or even rising!or even rising!

•• Most of the mass of Most of the mass of the galaxy is outside the galaxy is outside the solar circle!the solar circle!

•• But few stars, little But few stars, little gas theregas there……

•• DARK MATTERDARK MATTER ! ! probably in large probably in large halo halo ---- outweightsoutweightsstars+gasstars+gas by factorby factorof 3 to 10 of 3 to 10

Role of dark matter on rotation profileRole of dark matter on rotation profile

DARK MATTERDARK MATTER

Massive dark matter halo for MWMassive dark matter halo for MW

•• Stars and gas are Stars and gas are embedded in a embedded in a much larger much larger dark dark matter halomatter halo ????

•• DonDon’’t know what t know what dark matter is dark matter is yetyet…… probably probably not not baryonic baryonic (usual (usual protons, neutrons, protons, neutrons, electrons)electrons)

Dark matter halo for galaxiesDark matter halo for galaxies•• Presence revealed Presence revealed

by by rotation curvesrotation curves(motions of stars in (motions of stars in galaxy)galaxy)

•• Dark matter extends Dark matter extends beyond visible part of beyond visible part of the galaxythe galaxy ---- mass is mass is ~10x~10x stars and gas !stars and gas !

•• Most likely subatomic Most likely subatomic particles, as yet particles, as yet unidentified (unidentified (weakly weakly interacting massive interacting massive particles particles –– WIMPsWIMPs ?? ))

Magnificent spiral galaxy Magnificent spiral galaxy –– M51 WhirlpoolM51 Whirlpool

WhyWhy thethetwotwo--armedarmedSPIRALSPIRALPATTERN?PATTERN?