Transcript Astro 368 * Astrophysics II

Astro 368 – Astrophysics II
Lecture 2
Basics of Milky Way Structure
All Sky View (Visible Light)
Attempt #2 – Star Counting
Herschel (1738-1822) found that the Milky
Way was shaped something like a frisbee
15,000 light-years across with the Sun nearly
in the center.
Did correctly figure out that it was a disk!
Kaptyne Universe
• Galaxy 40,000 light years in size
• Sun 2,000 light years from center
• Density decreased from center
Why doesn’t this method work???
Hint:
The Milky Way in the Infrared
There is less absorption by dust in the infrared.
Multiwavelength Milky Way
Disk Component:
stars of all ages,
many gas and dust clouds
Spheroidal Component:
bulge & halo, old stars,
few gas clouds
All Spiral Galaxies are Flat!
About the same ratio of height to width as a CD
Two components: disk and spheroidal
Model of the Milky Way from IR data
Edge-on view of the Milky Way
1pc ~ 3ly
Fermi (Gamma Ray) Bubbles
Galactic Center
Stellar Streams in the Halo/Disk
Stellar Streams in the Halo/Disk
Hot Halo
Hot Halo
High Velocity HI