ASTR 1120ASTR 1120General Astronomy:General Astronomy:Stars & GalaxiesStars & Galaxies
!omework #6
on Mas"ring As#onom$due on Tuesday, %ov. 03, by 5p&
If your CU clicker grade is 0 and you have been in
class, please send your clicker # to TA Thomas Rogers
The Milky WayThe Milky Way
Size of the Milky WaySize of the Milky Way
•• 100-400100-400 billion stars
• 100,000 light years in
diameter
• Sun (and us) are
located ~28,000 light~28,000 light
yearsyears from the center,
in the ‘Orion Arm’
Artist’s sketch
Milky Way Milky Way AnatomyAnatomy –– Spiral Galaxy Spiral Galaxy
Disk, Bulge & HaloDisk, Bulge & Halo
•• DiskDisk:: includesincludes
spiral armsspiral arms ----
young, new staryoung, new star
formationformation
•• Bulge & HaloBulge & Halo::older stars,older stars,
globular clustersglobular clusters
Artist’s sketch
Disk is very thin!Disk is very thin!
What Milky Way What Milky Way mightmight look like! look like!
Spiral galaxy
NGC 4414
Galaxy NGC 4565 ! nearly edge-on
What kind of object lie in the What kind of object lie in the halohalo of our of our
Galaxy?Galaxy?
A. O and B stars.
B. Gas and dust.
C. Globular clusters
D. Open clusters.
E. All of the above.
Clicker QuestionClicker Question
What kind of object lie in the What kind of object lie in the halohalo of our of our
Galaxy?Galaxy?
A. O and B stars.
B. Gas and dust.
C. Globular clusters
D. Open clusters.
E. All of the above.
Clicker QuestionClicker Question
Where does most star formation occurWhere does most star formation occur
in the Milky Way todayin the Milky Way today??
A. In the halo
B. In the bulge
C. In the spiral arms
D. In the Galactic center
E. Uniformly throughout the MilkyWay
Clicker QuestionClicker Question
Where does most star formation occurWhere does most star formation occur
in the Milky Way todayin the Milky Way today??
A. In the halo
B. In the bulge
C. In the spiral arms
D. In the Galactic center
E. Uniformly throughout the MilkyWay
Clicker QuestionClicker Question
An important QuestionAn important Question
How do we know all we knowHow do we know all we know
about the Milky Way?about the Milky Way?
Mapping the Milky WayMapping the Milky Way
•• GalileoGalileo "For the Galaxy is nothing else than a congeries of
innumerable stars distributed in clusters."
•• William & Caroline HerschelWilliam & Caroline Herschel (1785): star counts
– Counted stars along 683 lines of sight using their 48-inch
telescope.
Conclusion: Sun is in the center
and MW width is about 5 times its thickness
6,500 ly
30,000 ly
ShapleyShapley’’s s globular clustersglobular clusters
• Harlow Shapely measured distances to globular clusters
– These appeared to be centered on a location tens of thousands oflight-years from the Sun.
Conclusion: Sun not in center, about 2/3 out
How Do Stars Orbit in Our Galaxy?How Do Stars Orbit in Our Galaxy?
Stars in the diskStars in the disk all orbit in the same all orbit in the same
direction with a little up-and-down motiondirection with a little up-and-down motion
• If they get too far above or below the disk, the gravity
of everything in the disk pulls them back in
Orbits of Orbits of stars in the bulge and halostars in the bulge and halo have have
random orientationsrandom orientations
• Evidence points to bulge and halo formed before
the disk existed
– Their orbits not affected (much) by the gravity of the disk
Why spiral arms?Why spiral arms?
““Density wavesDensity waves”” ––stars move in andstars move in andout of denserout of denserregionsregions
Like Like ripples in a pondripples in a pond
In dense regions,In dense regions, starstarformation is moreformation is moreintenseintense, , so so ““armsarms””are brighterare brighter
M51 - WhirlpoolM51 - Whirlpool
Why do orbits ofWhy do orbits of disk stars bob up anddisk stars bob up and
down?down?
A. They’re stuck to the interstellar mediumwhich moves like that because of its density.
B. The gravity of disk stars pulls toward disk
C. The halo stars push them back into disk
D. Their orbits carry them out but then theybounce off the edge of the Galaxy and headback in.
E. The density waves in the spiral arms kickthem out of the disk.
Clicker QuestionClicker Question
Why do orbits ofWhy do orbits of disk stars bob up anddisk stars bob up and
down?down?
A. They’re stuck to the interstellar mediumwhich moves like that because of its density.
B. The gravity of disk stars pulls toward disk
C. The halo stars push them back into disk
D. Their orbits carry them out but then theybounce off the edge of the Galaxy and headback in.
E. The density waves in the spiral arms kickthem out of the disk.
Clicker QuestionClicker Question
Galaxies: Ultimate Galaxies: Ultimate Recyling Recyling PlantsPlants
Which generation of stars do youWhich generation of stars do you
expect to be more metal-rich?expect to be more metal-rich?
A. Older population of stars (i.e. starsformed a very long time ago)
B. Younger population of stars (i.e.formed more recently)
C. No difference
Clicker QuestionClicker Question
Which generation of stars do youWhich generation of stars do you
expect to be more metal-rich?expect to be more metal-rich?
A. Older population of stars (i.e. starsformed a very long time ago)
B. Younger population of stars (i.e.formed more recently)
C. No difference
Clicker QuestionClicker Question
Contents: Contents: Cold stuffCold stuff
• Molecular CLOUDS
– Mostly atomic hydrogen,
some helium and other
molecules
• Dark, dusty, cold
– 10-30K
• Emit molecular
emission lines in far IR,
radio
•• Orion imageOrion image here inhere in
carbon monoxidecarbon monoxide (CO) (CO)
–– colors are Doppler shiftscolors are Doppler shifts
COCO
DopplerDoppler
ImagesImages
Molecular clouds =Molecular clouds =
star forming regionsstar forming regions
Mapping Mapping ColdCold Hydrogen Hydrogen
•• Even the coldestEven the coldest
hydrogen emitshydrogen emits
faint emission linesfaint emission lines
in thein the RADIORADIO
•• Change in Change in energyenergy
levels of nuclearlevels of nuclear
configurationconfiguration
•• Wavelength: Wavelength: 21 cm21 cm
All sky 21 cm radio mappingAll sky 21 cm radio mapping
Semi-Warm stuffSemi-Warm stuff
•• Dust:Dust:
–– absorbsabsorbs visible visible
and UV lightand UV light
–– TransparentTransparent to to
longlong
wavelengthswavelengths
(red, IR, radio)(red, IR, radio)
•• Emits IR lightEmits IR light
Horsehead Horsehead NebulaNebula
Dust+darkDust+dark
molecularmolecular
cloudsclouds
HorseheadHorsehead
in close-upin close-up
VLTVLT
(Very Large(Very Large
Telescope)Telescope)
•• Hot starsHot stars exciteexcite
atomic transitionsatomic transitions
in hydrogen andin hydrogen and
other light elementsother light elements
in the gasin the gas
•• T~ 10,000 K nearT~ 10,000 K near
hot young starshot young stars
Ionization nebulaeIonization nebulae
““O & B star O & B star
associationsassociations””
Lagoon NebulaLagoon Nebula
Hot stuffHot stuff
If we took a spectrum of the gas in anIf we took a spectrum of the gas in an
ionization nebula, what should weionization nebula, what should we
expect to see?expect to see?
A.A. A continuous spectrumA continuous spectrum
B.B. Emission lines of hydrogen plus a few otherEmission lines of hydrogen plus a few other
slightly heavier elementsslightly heavier elements
C.C. Emission lines ofEmission lines of elements all the way up toelements all the way up to
iron andiron and a lot of heavier elementsa lot of heavier elements
D.D. Absorption lines of a number of elementsAbsorption lines of a number of elements
E.E. Absorption linesAbsorption lines from hydrogen onlyfrom hydrogen only
Clicker QuestionClicker Question
A.A. A continuous spectrumA continuous spectrum
B.B. Emission lines of hydrogen plus a few other slightly heavierEmission lines of hydrogen plus a few other slightly heavierelementselements
C.C. Emission lines ofEmission lines of elements all the way up to iron andelements all the way up to iron and a lot ofa lot ofheavier elementsheavier elements
D.D. Absorption lines of a number of elementsAbsorption lines of a number of elements
E.E. Absorption linesAbsorption lines from hydrogen onlyfrom hydrogen only
Trifid Trifid nebula (M20)nebula (M20)
visiblevisible Spitzer infraredSpitzer infrared
Stellar nursery (Stellar nursery (Sharpless Sharpless 140)140)
Spitzer IR image shows deeply embeddedSpitzer IR image shows deeply embedded
O-type stars within dark dust cloud encasing themO-type stars within dark dust cloud encasing them
(10 (10 ly ly across)across)
Really Hot StuffReally Hot Stuff
Hot starHot star
winds fromwinds from
aging starsaging stars
SupernovaSupernova
RemnantsRemnants&&
PlanetaryPlanetary
NebulaNebula
More hot stuffMore hot stuff
Some stuff is Some stuff is REALLY HOTREALLY HOT
•• Bubbles of hot gasBubbles of hot gasblown out byblown out bySUPERNOVAESUPERNOVAE
•• T = tens of millionsT = tens of millionsof degrees Kof degrees K
•• Mixing with rest ofMixing with rest ofgalactic gas galactic gas !!enrichment withenrichment withheavy elementsheavy elements
Superbubbles Superbubbles & Fountains& Fountains
•• WhenWhen multiple bubblesmultiple bubblesjoin (from a cluster) theyjoin (from a cluster) theycan create can create superbubblessuperbubbles..
•• Superbubbles Superbubbles cancan blastblasthot gashot gas eveneven out of theout of theGalaxy!Galaxy!
•• ““EnrichesEnriches”” gas between gas betweengalaxiesgalaxies
•• Some will rain back downSome will rain back downand mix into the Galaxyand mix into the Galaxy
ArtistsArtists’’ conceptions! conceptions!
Edge-on view of spiral galaxy Edge-on view of spiral galaxy NGC 4013NGC 4013
•• Dust/gas in diskDust/gas in diskobscures lightobscures light
•• Plumes and fuzzPlumes and fuzzsticking out aresticking out are““fountainsfountains”” & &““superbubblessuperbubbles””from supernovaefrom supernovae
HSTHST
SuperbubblesSuperbubbles in spiral galaxy NGC 3079in spiral galaxy NGC 3079
HSTHST
Inside our Galaxy: Material isInside our Galaxy: Material is
Constantly Being RecycledConstantly Being Recycled
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