Milky Way (-like) Galaxy

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Milky Way (-like) Galaxy
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Milky Way Galaxy

• Eye 1. Sun Moon EARTH AS A SPINNING PLANET
• 2. planets SOLAR SYSTEM
• 3. nearby stars SOLAR NEIGHBORHOOD
• 4. white haze of sky MILKY WAY GALAXY
• Greek galactos milk
• thickest in Sagittarius, through Cygnus,
  Orion
• dark bands obscuration
• star clusters nurseries
• Galileo first resolved into stars
• WE ARE INSIDE IT

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Milky Way from Inside
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Milky Way Galaxy

• Members stars 1011 to 1012
• entire HR Diagram
• not stars
• white dwarfs, neutron stars, black holes
• brown dwarfs
• rocks
• solar systems, planets, asteroids, KBOs,
  comets
• gas/dust
• nebulae, ISM, GMCs
• life

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Herschels Milky Way
History pre-20th century no idea there were
galaxies Herschel star count model
pre-parallaxes, HR assumptions (a) Sun at
center (b) all stars identical (c) no
obscuration result much too small
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Galactic Scales
Galactic Scales
Spiral Nebulae like Andromeda individual baby
stars but, no parallax measured
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Clues to the MW Mystery
Variable Stars small fraction of all
stars eclipsing two stars novae/supernovae
sporadic pulsating intrinsic, regular HR
Instability Strip
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Distance Ladder Rung 4
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Shapley Solves MW Mystery
Globular RR Lyrae variables Clusters found
GCs at great distances spherically
symmetric EUREKA! center of GCs center of
MW
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Milky Way Map
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Milky Way Territories
DISK 30000 x 300 pc 1001 arms last young Pop
I blue/white 2 metals open clusters gas/dust/
formation merry-go round
BULGE 4000 x 6000 pc football bar mixed mixed
Pops yellow massive BH gas/dust ring random
spiral
HALO 50000 pc spherical edge? first old Pop
II red 0.02 metals globular clusters no
gas/dust/planets electron-like disordered

• size
• details
• origin
• stars
• contents
• motion

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Milky Way Formation
Four Phases 1. early star formation in ENORMOUS
contracting cloud GCs as substantial
blobs halo stars old halo stars have random
motion size of halo slight halo
rotation 2. collapse of gas to disk no
gas/young stars 3. star formation in disk
young stars now 4. cannibalization of other
galaxies/GCs star streams HALO FIRST DISK
LAST
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Formation
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Star Motions
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Andromeda Galaxy
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Spiral Arms
Tracers 21 cm emission of H atom CO in
GMCs Scale Sun is 8 kpc from center of
MW stars, GCs, arms, observed to radius of 15
kpc gas observed to radius of 25
kpc Formation? cohesive arms would wind up and
disappear
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Spiral Arms
Formation? cohesive arms would wind up and
disappear Density Waves gas moves into
ripple compresses stars form Causes
galaxy collisions? companion galaxy
tides? bar-like asymmetry of rotating
bulge? gas instability near the
bulge? Observe patterns not mass movement!
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Spiral Traffic
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Milky Way Rotation
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Missing Mass
Rotation Curve orbital velocity vs.
distance curve RISES even beyond where we see
stars more mass than seen out to 40 kpc
(at least)
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Missing Mass
Conclude gt twice as much mass as can be
seen dark matter dark at all wavelengths Candid
ates black holes need lots of big
stars white dwarfs burned out regular
stars red/brown dwarfs need
lots subatomics hard to test mixture?
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Milky Way Center
center of GC distribution center of gas
distribution 8 kpc away
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Milky Way Center
Contents 50000 stars/cubic parsec million X
local! stellar encounters and
crashes molecular gas ring, diameter 400
parsecs Ground Zero bright radio source Sgr
A X-rays, gamma rays energetic hot gas at
10000 K heating extended filaments magnetic
fields flickering small fast moving
gasstars MASSIVE
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Milky Way Center
see the movie!
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Answer?
1 million Msun 0.02 AU 4 Rsun SUPERMASSIVE
BLACK HOLE
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Milky Way Today
THIS IS AN ARTISTS CONCEPTION!
.
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Milky Way Today
Milky Way Today
THIS IS REAL!
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