1. The Dark Side of the Universe
Lecture 26

2. Homework Read Ch. 24: Life in the Universe
HW: MasteringAstronomy Chapter 24

3. Final Exam Time: Thursday, Dec 13 at 11:30am in VLSB2050. Topics:
- 25% material covered before midterm 1.
- 25% material covered between midterms 1 and 2.
- 50% material covered after midterm 2.
Review Session:  Tuesday, Dec 4 at 5pm in VLSB2050 (same room)

4. Discussion Sections and Office Hours

5. Thank you for evaluating the course and me (Prof. Geoff Marcy)!
Student Evaluations
Thank you for evaluating the course
and me (Prof. Geoff Marcy)!
Instructor: Geoff Marcy
Course: C12
Semester: Fall 2012

6. The Dark Side of the Universe
Lecture 26

7. Most of the Universe is Dark
You, me, stars,
grey matter,
white matter,
antimatter…

8. How do we know the Universe is Dark?
Example 1: Stars would be moving too fast
if there were only luminous matter
Mercury
Earth
Jupiter
Solar System:
“Keplerian orbits”

9. How do we know the Universe is Dark?
Example 1: Stars would be moving too fast
if there were only luminous matter
Galaxies:
“Flat rotation curve”

10. How do we know the Universe is Dark?
Example 2: Bending of light - gravitational lensing

11. How do we know the Universe is Dark?

12. How do we know the Universe is Dark?
Four images of the same galaxy

13. How do we know the Universe is Dark?

14. How do we know the Universe is Dark?

15. How do we know the Universe is Dark?
Example 3: Cosmic Microwave Background
CMB: very cold ( C, F) and nearly uniform relic radiation left over from the hot big bang

16. How do we know the Universe is Dark?
Example 3: Cosmic Microwave Background
If you had microwave eyes:
(1965)

17. (1992) 17
(2010)

18. How do we know the Universe is Dark?
White points:
WMAP (2010)
7-year data
Red curve: Theoretical prediction for a universe made of
73% dark energy, 23% dark matter, 4% atoms

19. How do we know the Universe is Dark?
Example 4: Distant supernovae
After
Before 19

20. How do we know the Universe is Dark?
Example 4: Distant supernovae
are standard candles

21. How do we know the Universe is Dark?
Example 4: Distant supernovae
are standard candles

22. How do we know the Universe is Dark?
Kowalski et al (2008)
Supernovae probe
Dark Energy
CMB probes
Concordance region:
73% dark energy
23% dark matter
4% atoms
Dark Matter

23. What can dark matter be? Planets?
Not enough mass: even Jupiter weighs only
0.1% of the Sun
Rocks, gas, oceans are all made of quarks.
The “normal” stuff cannot be > 4%.

24. What can dark matter be? Black Holes?
Graveyards of massive stars, but massive stars are rare and made of normal atoms.
Once formed, black holes suck in normal matter.
So you can’t hide much dark matter in it.

25. What can dark matter be? Anti-matter?
Antimatter and matter have identical mass but opposite quantum numbers (electric charge, spin…)
Antimatter and matter annihilate each other into flashes of easily detectable gamma rays
Recall PET = Positron Emission Tomography
Hardly “dark” !

26. What can dark matter be? WIMPs Top candidate:
But it takes more than wimps to find WIMPs!
Direct Detection: CDMS-II, Edelweiss etc
Accelerator: Large Hadron Collider

27. Cryogenic Dark Matter Search

29. Supernova Explosions as Standard Candles
Type Ia supernovae, which give off a standard amount of light.
The distance to the galaxy that contains the supernova: Compare how bright they know the explosion should be
with how bright the explosion appears. Using the inverse square law of light, they can
compute the distance to the supernova and thus to the supernova's home galaxy.

31. Accelerating Expansion of the Universe: Dark Energy

32. Large
Hadron
Collider
(17 mile tunnel)

33. Most of the Universe is Dark
???
You, me, stars,
grey matter,
white matter,
antimatter…
WIMPS ?