1. Astronomy 100 Tuesday, Thursday 2:30 - 3:45 pm Tom Burbine tburbine@mtholyoke.edu www.xanga.com/astronomy100

2. OWL assignment (Due Today) There is be an OWL assignment due on Tuesday April 5 at 11:59 pm. There are 15 questions and a perfect score will give you 2 homework points.

3. Exam 40 Questions Chapters 15, 16, 17, and 18 Some of the questions are taken straight from OWL questions

4. Other Room April 7th Goessmann 0020 2:30-3:45 PM Last Names beginning with H, I, J, and K

5. Things you should know Layers of the Sun Hydrogen Fusion Hertzsprung-Russell Diagram Stellar Classifications Life Cycle of the Sun Helium Fusion CNO cycle What happens to stars as they “die”

6. Review Session Wednesday-Review Session –Hasbrouck 134 from 7-8 pm –I will be there at 6 pm if you want to talk to me in a much smaller group

7. PRS Questions

8. PRS question #1 What is approximately the temperature of the plasma in a sunspot? –A) 2,000 K –B) 4,000 K –C) 6,000 K –D) 8,000 K –E) 10,000 K

9. PRS question #1 What is approximately the temperature of the plasma in a sunspot? –A) 2,000 K –B) 4,000 K –C) 6,000 K –D) 8,000 K –E) 10,000 K

10. PRS Question #2 Which of these spectral types have the strongest hydrogen emission lines in their spectra? –A) O –B) B –C) A –D) F –E) G

11. PRS Question #2 Which of these spectral types have the strongest hydrogen emission lines in their spectra? –A) O –B) B –C) A –D) F –E) G

12. “Deaths” of Stars White Dwarfs Neutron Stars Black Holes

15. White Dwarfs White Dwarfs is the core left over when a star can no longer undergo fusion Very dense –Some have densities of 3 million grams per cubic centimeter –A teaspoon of a white dwarf would weigh as much as an elephant

16. White Dwarfs Some white dwarfs have the same mass as the Sun but slightly bigger than the Earth 200,000 times as dense as the earth

17. White Dwarfs Collapsing due to gravity The collapse is stopped by electron degeneracy pressure

18. Electron Degeneracy Pressure No two electrons can occupy the same quantum state

19. Electron Degeneracy Pressure As electrons are moved closer together Their momentum (velocity) increases Due to Heisenberg Uncertainty Principle

20. So What Does This Mean Electron Degeneracy Pressure balances the gravitational force due to gravity in white dwarfs

21. One Interesting Thing More massive white dwarfs are smaller

22. White Dwarf Limit The mass of a White Dwarf can not exceed approximately 1.4 Solar Masses Called the Chandrasekhar Limit Electrons would have velocities greater than the speed of light

23. The Sun Will end up as a White Dwarf

24. Neutron Star Neutron stars are usually 10 kilometers acroos But more massive than the Sun Made almost entirely of neutrons Electrons and protons have fused together

25. How do you make a neutron star? Remnant of a Supernova

26. How do you get a Supernova? A high-mass star keeps on fusing elements into ones with larger atomic masses Is now a Red Supergiant Energy keeps on being released since the mass of the new nucleus is less than the original ones

28. This stops with Iron Fusion of Iron with another element does not release energy Fission of Iron with another element does not release energy So you keep on making Iron

30. Initially Gravity keeps on pulling the core together The core keeps on shrinking Electron degeneracy keeps the core together for awhile

31. Then The iron core becomes too massive and collapses The iron core becomes neutrons when protons and electrons fuse together

33. Density You could take everybody on Earth and cram them into a volume the size of sugar cube

34. Explosion The collapse of the core releases a huge amount of energy since the rest of the star collapses and then bounces off the neutron core 10 44-46 Joules Annual energy generation of Sun is 10 34 Joules

35. How do we know there are neutron stars? The identification of Pulsars Pulsars give out pulses of radio waves at precise intervals

36. Pulsars Pulsars were found at the center of supernovae remnants

37. Pulsars Pulsars were interpreted as rotating neutron stars Only neutron stars could rotate that fast Strong magnetic fields can beam radiation out

39. Black Holes If a collapsing stellar core has a mass greater than 3 solar masses, It becomes a black hole

40. Black Hole After a supernova if all the outer mass of the star is not blown off The mass falls back on the neutron star The gravity causes the neutron star to keep contracting

41. Black Hole A black hole is a region where nothing can escape, even light.

42. Event Horizon Event Horizon is the boundary between the inside and outside of the Black Hole Within the Event Horizon, the escape velocity is greater than the speed of light Nothing can escape once it enters the Event Horizon

43. How do calculate the radius of the Event Horizon? It is called the Schwarzschild Radius Radius = 2GM/c 2 This is a variation of the escape velocity formula Escape velocity = square root (2GM planet /R planet )

44. Black Hole Sizes A Black Hole with the mass of the Earth would have a radius of 0.009 meters A Black Hole with the mass of the Sun would have a radius of 3 kilometers

46. Can you see a Black Hole?

47. No Black Holes do not emit any light So you must see them indirectly You need to see the effects of their gravity

48. Evidence The white area is the core of a Galaxy Inside the core there is a brown spiral- shaped disk. It weighs a hundred thousand times as much as our Sun.

49. Evidence Because it is rotating we can measure its radii and speed, and hence determine its mass. This object is about as large as our solar system, but weighs 1,200,000,000 times as much as our sun. Gravity is about one million times as strong as on the sun. Almost certainly this object is a black hole.

50. Questions