ASTR 1102 Lecture : Lecture22
Document Summary
Thermal pressure drops and core contracts white dwarf. Don"t confuse with red dwarf or brown dwarf. Electrons in atoms can only have certain energies. This is why we see sharp absorption lines - electron changes energy. Quantum physics says free electrons also have energy levels. Normally this is unimportant - levels sparsely filled. At high enough densities, the electron levels fill up: gas becomes degenerate. Gas is then degenerate - all levels are full. Electrons have nowhere to go - incompressible. Strong enough gravity can overcome degeneracy pressure. A degenerate core of more than 1. 4m will collapse. Gravity contracts core until it cannot contract any more. Degeneracy pressure (again) supports the core, halts collapse. It is now a white dwarf, perhaps half mass of sun, but the size of the earth - hot, but low-luminosity. One teaspoon of white dwarf matter would weigh 5. 5 tons (=1 elephant!) Maximum mass of a white dwarf is 1. 4m .
