15_White_Dwarfs - 15 White Dwarfs The Plan The White Dwarf Cooling curve Why arent any WDs with Mass less than M<0.4MSun Over loading a WD to cause

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15 – White Dwarfs S. Chandrasekhar Chandrasekhar ~1970 2 The Plan • The White Dwarf Cooling curve? • Why aren’t any WDs with Mass less than M<0.4M Sun ? • Over loading a WD to cause its core to collapse is the source of Type Ia supernova. 3 Cooling Time of a White Dwarf #1 2 The electrons cannot do much. They are locked into the degenerate gas. The nuclei, alpha particles, carry the heat. 1 : macroscopic 2 3 : microscopic 2 is the number of al thermal GM E R NkT N = = 2 2 pha particles in the star 1 3 3 2 2 2 1 2 2 3 1 1 3 th M N m GM M NkT kT E R m m GM T R Mk GMm T R k α = = = = = = 4 Cooling Time of a White Dwarf #2 2 4 2 4 2 3 1 3 9 3 3 L=4 R ~ 8 3 8 4 R 3 1 : T T 8 4 R 3 10 10 WDs cool so slowly that none are seen with T 3500K. It's a double wammy since the p cooling p p dE Mk dT T dt m dt Mk T t m T Mk m T T x yr K π σ τ - = Δ = Δ = Δ MS star is low mass, and it stays on the MS for a long time!
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5 Cooling Time of a White Dwarf #3
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This note was uploaded on 04/05/2009 for the course ASTRO 3332 taught by Professor Houck,j during the Spring '09 term at Cornell University (Engineering School).

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15_White_Dwarfs - 15 White Dwarfs The Plan The White Dwarf Cooling curve Why arent any WDs with Mass less than M<0.4MSun Over loading a WD to cause

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