2. 11 Black Holes and General Relativity Stuff that warps your mind

3. 11 Goals Use the Scientific Method: What proof is there of black holes? What proof is there that black holes are black? Why should light be affected by gravity? What proof is there that it is?

4. 11 Black Holes Mass so great that the velocity needed to escape is greater than c. Need lots of mass in a small volume.

5. 11 Seeing Black Holes Rips apart and heats up anything it swallows. Very hot  thermal emission peak in X-rays. So what do you look for: –Massive –Small –Dark in visible –Bright in X-rays

6. 11 Cygnus X-1 1970s Intense source of X-rays. “Near” star HDE226868.

7. 11 HDE226868 Doppler shifts of HDE226868 Like before, we get mass of star and unseen companion.

8. 11 The Companion Result: Period = 5.6 days Total Mass ~ 28 x M sun From spectral type of HDE226868 we estimate its mass ~18 M sun. Companion M = 10 M sun ! Massive! But where is its light? Dark! Can’t be a normal star, or even neutron star.

9. 11 X-ray Source? Star brightness fluctuates every 5.6 days. X-rays drop off every 5.6 days! Companion must be source of X-rays! R EH = 30 km!

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11. 11 Supermassive Black Holes Photograph the center of a galaxy. Make spectrum of light from center. Velocity Distance

12. 11 Heart of Darkness From Doppler shift get a velocity. From picture get a separation. From Kepler’s Laws get a Total Mass.

13. 11 The Dark Truth Observe: V = 400 km/s within 26 LY of center. So: –Period = 121,600 yrs –Separation = 26 LY = 1,600,000 AU Total Mass in central pixel: 300,000,000 x Mass of Sun! But where’s all the light? Small, massive, dark  black hole? R EH = 6.5 AU!

14. 11 Monster in the Milky Way? IRAS – Milky Way

15. 11 200 pc 5 pc Sagittarius A* - Sgr A*

16. 11 Stars in Motion The “+” is the radio source Sgr A* Measure Velocities. Measure distance from “+” Assume circular orbits. Calculate: –Period (yrs) –Separation (AU) Copyright Eckart & Genzel

17. 11 Kepler’s Laws Conclusion: Must be over one million solar masses within less than 1/5 of a light year! But we don’t see over a million stars in the picture.

18. 11 Small, Dark and Massive Supermassive Black Hole! For M = 1,000,000 x M sun R EH = 3,000,000 km = 0.02 AU! Probably in the centers of all spiral galaxies.

19. 11 Are Black Holes Black? Why should light be affected by gravity? Newton - “Whenever you have mass you have gravity.” But light has no mass! Einstein’s General Theory of Relativity (1915): –New way of looking at gravity. –Allows gravitational effects on light.

20. 11 General Relativity 2 Main Postulates: 1. The speed of light is always c. Thou shalt not add your speed to the speed of light!

21. 11 General Relativity 2. Accelerating reference frames are indistinguishable from a gravitational force. The Star Tours ride at Disneyland is awesome!

22. 11 Gravity Bends Light

23. 11 Is there Proof? Scientific Method: 1.Hypothesis: predict gravity bends light. 2.Test: The Sun has a lot of gravity and should deflect star light.

24. 11 Solar Eclipse of 1919 Hard to see stars near the Sun. Can see stars near the Sun during an eclipse. Can predict time and position of Sun during eclipse years in advance. Measure the positions of stars 6 months before when they are up at night. During eclipse, measure their positions again. SOHO spacecraft Result: Theory of Relativity confirmed!

25. 11 Gravitational Lensing If geometry right: gravity cause multiple images.

26. 11 Einstein Lenses Copyright – J. Rhoads, WIYN Copyright – Charles R Evans (UNC) Einstein Ring Copyright – L. J. King (U. Manchester)

27. 11 Copyright – A. Fruchter (STScI) Abell 2218

28. 11 Space is Curved Einstein said to picture gravity as a warp in space. –Sagan : A “pucker” in fabric of space. Kepler’s Laws can all be explained by movement around “puckers.” Everything moving is affected, regardless of mass.

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30. 11 Gravity makes time slow S F S F