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Gravitational contraction Q

  1. Feb 10, 2008 #1
    1. The problem statement, all variables and given/known data
    The gravitational potential energy W of a self-gravitating sphere of mass M and radius R depends on the detailed distribution of mass within the sphere, but it is generally of order of magnitude -GM^2/R. For the Sun, W_sun = -2G(M_sun)^2/R. What is the timescale
    t = -(1/2)(W_sun)/(L_sun) over which gravitational contraction could have supplied the power radiated by the sun at it's present rate?

    please give some hints, thanks a lot.
  2. jcsd
  3. Feb 10, 2008 #2


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    what is L_sun ?

    (iknow that it is Luminosity, but try to find the value)
  4. Feb 10, 2008 #3

    thanks for the reply. But I didn't understand what was your hint... :)
  5. Feb 11, 2008 #4


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    I meant, have you tried just to plug in the value of L_sun into that eq?
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