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Unformatted text preview: For a nonrelativistic ideal gas: 2E KE = − E GR – E tot = − E KE & E tot = E GR /2 • For an extreme relativistic ideal gas: E KE = − E GR – E tot = 0 KelvinHelmholtz time • t KH = E tot /dE/dt = E tot /L is a characteristic time for change. • Using the virial theorem: – t KH = E GR /2/L = (q/2)(GM 2 /LR) – è t KH = (2 × 10 7 yrs)(M/M ¤ ) 2 (L/L ¤ ) − 1 (R/R ¤ ) − 1 • Thus: t KH << t dyn – Changes happen slowly and use of virial theorem is justified afterthefact. • Why is t KH << t dyn ? Time for photons to escape the Sun • Free streaming: t = R/c • But the Sun is opaque, so photons must diffuse out: radiative diffusion....
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This note was uploaded on 02/06/2012 for the course PHYSICS 441/541 taught by Professor Pryor during the Spring '12 term at Rutgers.
 Spring '12
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