What is this? [picture is in the infrared]
The neighborhoods in the Milky Way and who lives there
The halo - globular clusters, population II (low metal) stars
The disk – stars like the sun, pop I (high metal) stars
Spiral Arms O, B stars, HII regions, HI, GMC
Dark matter is all of them [but halo has most]
Where you live is determined by the circles you move in.
Our companions : Large Magellanic Cloud; Small Magellanic Cloud
Sagittarius Dwarf; Canis Major Dwarf
Chemical composition
70% H 28% He 2% metals
and changing the star-gas–star cycle
Stellar death Planetary nebulae and Supernovae spectra
are part of it but so are stellar winds
SN show up in x-ray (shock waves) and radio also
New elements show up in emission
Superbubbles and fountains. model We are in the Local Bubble
Cooler stuff
H the 21 cm line
Where are the stellar nurseries? Look for the ionization nebulae.
and the account sheet
How much mass is in the Milky Way?
Kepler again to determine mass
BUT What about a disk with mass not just at the center?
So what do we see? the rotation curve
Why doesn’t the matter quit? Dark matter
Why a spiral?
In some way it is an illusion. What are you seeing?
The older components are much smoother
But
spiral
density wave concentrates
matter there.
How did the Galaxy form?
Populations hold the key.
Disk population –open clusters, dust, GMC, etc. young
Spherical population globular clusters, low metal stars, etc. old
Disk forms
Arms form
Today still some collisions
The Galactic Center
How do we know where it is?
Shapley’s globular clusters and 21cm line
Views 300pc IR and 600pc radio
100pc radio loops SgrA* accretion 1pc IR stars
Is SgrA* a supermassive black hole?
![What is this? [picture is in the infrared]](http://hal.physast.uga.edu/%7ejss/1020/ch19/19What1.jpg){kind=link}
![What is this? [picture is in the infrared]](http://hal.physast.uga.edu/%7ejss/1020/ch19/19What2.jpg){kind=link}
