Lecture5 - For a non-relativistic ideal gas 2E KE = − E...

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Lecture 5 January 31, 2012 Introduction to Stellar Structure and Evolution Properties of Stars
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News Hand in reviews of faculty candidate talks by today. First homework due Friday, February 3 rd Available on class website Can discuss the homework with classmates, but solutions should be in your own words. If you are having difficulty with a problem, you are encouraged to discuss it with me. Office hour: Thursday 3-4 PM, 302W Serin; or email me to see when we can meet.
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Virial Theorem <P> = (1/3) ( E GR /V) E GR = q(GM 2 /R), where q is a dimensionless integral that depends on the internal distribution of mass. For Sun, q 3/2. Thus, <P> = (1/3)[q(GM 2 /R)]/(4 π R 3 /3) = (q/4 π )(GM 2 /R 4 )
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Unformatted text preview: For a non-relativistic 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 Kelvin-Helmholtz 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 after-the-fact. • 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.

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Lecture5 - For a non-relativistic ideal gas 2E KE = − E...

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