1. Physics 55 Monday, November 14, 2005 1.Quiz 6 2.The evolution of low-mass and high-mass stars. 3.Where elements come from: nucleosynthesis. 4.Corpses of stars: white dwarfs, neutron stars, and black holes.

2. Two Key Ideas for Evolution of Stars 1.Radius and temperature of core vary in opposite ways than radius and surface temperature of the star. 2.Quantum degeneracy pressure from electrons becomes important as core density increases. Solar thermostat does not work for quantum pressure.

3. Electron Degeneracy Pressure

4. Evolution of Main Sequence Stars Two cases: Low-mass stars M < 2M Sun High-mass stars M > 8M Sun Intermediate mass 2M Sun < M < 8M Sun evolve like high- mass but end up like low-mass stars. Differences: Low-mass stars produce He, C, O, end up as white dwarfs, produce planetary nebula. High-mass stars produce all the other elements, end up as neutron stars or black holes.

5. Evolution of Low-Mass Star M < 2 M Sun

6. Helium Nuclei Fuse into Carbon Nuclei Crucial mysterious 7.6 MeV excited state in 12 C nucleus key to formation of higher elements!!! Rate of C fusion goes as T 30, extremely sensitive to temperature.