Lecture 31. Dark Matter, Misc., & Cosmology
Lecture 31. Dark Matter, Misc., & Cosmology
A. Class Business
-
Review topics*, on main web page
- Readings list*, also on main page
- Homework 6. questions after this lecture
- Homework 6. due at end Friday morning's class --
NO LATE WORK ACCEPTED:
solutions posted IMMEDIATELY after class
B. Dark Matter
Q: How is mass in the Milky Way distributed?
A: It's not all within the visible part of the galaxy!
C. Quasars -- Quasi-Stellar Objects
(QSO's)
-
APOD Image Gallery*
-
very far* -- 15 byr, from redshift of spectral lines
-
very energetic* (must be for us to see!)
- more than 1 billion Suns!
- Why so bright?
- Black holes swallowing up mass?
- Galaxies colliding?
- being FARTHEST and BRIGHTEST warrants studying QSO's
D. Cosmic Microwave Background (CMB)
Q: Recall that all objects above absolute zero radiate
as blackbodies. How does the universe radiate?
Q: How did it get so cold? (or: so warm?)
HINT: When gases EXPAND freely, they COOL
-- cook with a propane tank in humid weather,
and frost forms on tank
Why? The total energy in a gas is depends on
- amount of energy each particle has (= speed = temp.)
- total number of particles.
If you take a WARM gas and spread its energy
over a large volume, the resulting diffuse gas is COLD.
(few % of snow "in between" TV channels is CMB)
E. Cosmology