1. Lecture 33- What’s the Milky Way made of?
M74: a Milky Way analog

2. How is the mass distributed?
How could we tell?

3. Force of Gravity acts on the Sun and all objects in the Galaxy
Gravity has magnitude and direction

4. Sun responds to net force by moving on circular path around the galactic center

5. Mass distributions like 1,2, and 3 give circular orbits with V(R)

6. The Observed Case for the Milky Way
No sign of the “root-R falloff”

7. Significance of the Rotation Curve for the Milky Way
Rotation curve stays high outside the bulk of the stars
Mass indicated by the rotation curve exceeds that in stars
Most of the mass of the Milky Way is in an unknown form of “Dark Matter”

8. The New View of the Milky Way
Dadark matter halo

9. Dark Matter: A Major Problem for Contemporary Physics and Astronomy
Stars are a small fraction of the mass of major galaxies
The dark matter problem becomes more pronounced as you go out in the universe
The form of the dark matter is unknown; probably not what you studied in chemistry
Possibly/probably an unknown form of elementary particle