1. Milky Way (-like) Galaxy

2. Milky Way Galaxy WE ARE INSIDE IT
Eye 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

3. Milky Way from Inside

4. 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

5. Herschel’s 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

6. Galactic Scales Galactic Scales
Spiral Nebulae like Andromeda
individual baby stars
but, no parallax measured

7. Clues to the MW Mystery Variable Stars small fraction of all stars
eclipsing … two stars
novae/supernovae … sporadic
pulsating … intrinsic, regular
HR “Instability Strip”
pulsate because of changing opacity

8. Distance Ladder Rung #4

9. Shapley Solves MW Mystery
Globular RR Lyrae variables
Clusters found: GCs at great distances
spherically symmetric
EUREKA! … center of GCs = center of MW

10. Milky Way Map

11. Milky Way Territories DISK BULGE HALO size details origin stars
30000 x 300 pc
100:1
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 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

12. Milky Way Formation HALO FIRST … DISK LAST
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

13. Formation

14. Star Motions

15. Andromeda Galaxy

16. 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 …

17. 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!

18. Spiral Traffic

19. Milky Way Rotation

20. 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)

21. Missing Mass Conclude > twice as much mass as can be seen
dark matter dark at all wavelengths
Candidates black holes … need lots of big stars
white dwarfs … burned out regular stars
red/brown dwarfs … need lots
subatomics … hard to test
mixture?

22. Milky Way Center center of GC distribution center of gas distribution
8 kpc away

23. 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 K … heating
extended filaments … magnetic fields
flickering … small
fast moving gas+stars … MASSIVE

24. Milky Way Center
see the movie!

25. SUPERMASSIVE BLACK HOLE
Answer?
1 million Msun
0.02 AU = 4 Rsun
SUPERMASSIVE BLACK HOLE

26. Milky Way Today
THIS IS AN
ARTIST’S
CONCEPTION! .

27. Milky Way Today Milky Way Today
THIS IS
REAL!

28. …………………………………..