The Dark Side of the Universe

1. The Dark Side of the Universe Lecture 26

2. Announcements • Homework • Read Ch. 24: Life in the Universe • Mastering Astronomy: Chapter 24 • Due Friday, Dec 6, at 6pm • Today’s lecture covers Ch. 22: • All you need to know is in the lecture. • Winter Break: Read Chapter 22 for fun.

3. Final Exam:Thursday, Dec 19, 11:30-2:30 RSF Field House: Main Floor Gym • Multiple Choice • All Chapters: 1-5, 9-14, 24 & All Lectures. • Emphasis on Chapters 12, 13, 14, 24 • Review Sessions: • Tue and Thu (Dec 10 & 12) at 5-6:30 • in 2040 VLSB • Come with questions !

4. The Dark Side of the Universe Lecture 26

5. You, me, Earth, Planets, stars Most of theUniverse is Dark

6. How do we know the Universe is Mostly Dark ? Example 1: Gravity by Central Mass (Sun) determines orbital speed of planets. Mercury Venus Orbital Speed = G M / Distance Earth Mars Jupiter Solar System: “Keplerian orbits”

7. How do we know the Universe is Mostly Dark ? Gravity by Central Mass (galaxy) determines orbital speed of stars. Orbital Speed = G M / Distance Galaxies: “Flat rotation curve”

8. How do we know the Universe is Mostly Dark ? Gravity by Central Mass (galaxy) determines orbital speed of stars. Orbital Speed = G M / Distance • Speed doesn’t fall ! • Mass, M, must be • increasing outward! Galaxies: “Flat rotation curve”

9. How do we know the Universe is Mostly Dark ? Example 2:Gravitational Bending of Light by Mass Light Source Telescope

10. How do we know the Universe is Mostly Dark ?

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

12. How do we know the Universe is Mostly Dark ?

13. Planets? What can dark matter be? Not enough mass: even Jupiter weighs only 0.1% of the Sun

14. Black Holes? What can dark matter be? 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.

15. Anti-matter? What can dark matter be? 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

16. What can dark matter be? Top candidate: Elementary Particles: Yet to be discovered !

18. Dark Energy

19. Supernova ExplosionsasStandard 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.

20. How do we know the Universe is Dark? Example 4: Distant supernovae After Before 20

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

25. You, me, Earth, Planets, stars Most of theUniverse is Dark

26. How do we know the Universe is Dark? Example 3: Cosmic Microwave Background CMB:very cold (-270.275 C, -454.495 F) and nearly uniform relic radiation left over from the hot big bang

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

28. (1992) 28 (2010)

29. 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

30. Accelerating Expansion of the Universe:Dark Energy

31. 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