1. Agenda Read Unit 8 Distance to galaxies (review) Redshift Hubble’s Law The Big Bang

2. Calculating distances to other galaxies Two standard candles: Cepheid variable stars Type I supernovae

3. NASA 10 billion ly away!

4. Cepheid variables Gene Smith, UCSD/CASS Cepheids are a standard candle. Discovered by Henrietta Leavitt. (photo: AAVSO)

5. Harvard Supernovas in 4 galaxies

6. How do we determine whether a galaxy is approaching or receding? The Doppler Effect. Next step: velocities

7. Demonstration: doppler buzzer How does the buzzer sound change as it moves away? A. Louder B. Softer C. Higher pitch D. Lower pitch

8. Source moving away from you The light is shifted toward the red: longer wavelength, lower pitch (frequency)

9. Source moving toward you The light is shifted toward the blue: shorter wavelength, higher pitch (frequency)

10. What about galaxies? Galaxies have specific spectral lines that can be identified. Measure wavelength. Compare to the “rest” wavelength. The difference is the doppler shift. From doppler shift we get speed.

11. Hubble’s distance velocity relation (Distance from us) (Speed at which galaxy recedes from us)

12. Two years later (note scale)

13. Hubble’s law The more distant a galaxy is, the faster it’s receding This means it has a larger redshift!! The universe is expanding!

14. The universe: Is expanding (Hubble’s law) Has galaxies evenly distributed throughout (homogeneous) Contents evolve with time (H fuses to He, etc) Any theory must be consistent with these facts!

15. Space is getting bigger! Wikipedia

16. The universe has no center Consider only the surface of the balloon

17. The big bang An explosion of space, not in space  A consequence of relativity Some heat is left over from this  Cosmic background radiation  Seen everywhere in the universe

18. How old is the universe? How can we estimate?  Precisely map the expansion seen now from Earth  Run the physics “backwards” Many ways to check. Examples:  Age of oldest stars (globular clusters)  WMAP measurements => 13.7 Billion years (plus or minus 1%)

19. Boomerang team Tiny differences in temperature seen in every direction!

20. The universe is 2.73 K +/- 0.0001 WMAP The whole sky is filled with radiation left over from the Big Bang

21. What if this heat comes from galaxies and clusters? How would the heat be distributed in the night sky?

22. What is the ultimate fate of the universe? Possibilities to consider: Big Crunch Growth will slow down Growth will remain constant Growth will continue to speed up

23. NASA Evidence suggests this is happening

24. Summary The universe is expanding Actually, it’s speeding up! Heat from the Big Bang is seen The matter in the universe in changing with time (because of stars)

25. What is the universe made of? Dark matter 25% Free H and He 4% Stars 0.5% Neutrinos 0.3% Heavy elements 0.03% Dark energy 70%Pie chart From Wikipedia

26. Group activity #10 Hubble’s law