18
Disk vs.
Halo Orbits
–The
Disk Component
•Stars,
gas, and dust
–The
spiral arms
•Size:
–Luminous
Diameter ~ 25 kpc
–Thickness
300 pc – 1 kpc
O stars
and dust smaller
Sun-like
stars greater
–The
Spherical Component
•Old
Stars, but little gas or dust
•The
Halo
–Globular
clusters
–Isolated
old stars
»red
dwarfs, giants, white
dwarfs
•The
Nuclear Bulge
From our text: Horizons, by Seeds