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Quasar Help

  1. Nov 24, 2009 #1
    1. The problem statement, all variables and given/known data

    If a quasar varies on a time scale of four months, how does the maximum size of the emitting region compare with the Schwarzschild radius for a 109 MSun black hole?

    2. Relevant equations

    3. The attempt at a solution

    Calculating the S radius of the black hole is trivial, but I think I missed the lecture on varying quasars. I don't know of any equations for 'emitting regions' let alone how to use its rotation period to do so. Can anyone start me off on the right track?

    fwiw I calculated the S radius by the eqn 3km(M/Msun) = 3 x1012 m
  2. jcsd
  3. Nov 24, 2009 #2


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    if the source varies on a time scale of 4months whats the maximum size it can have?

    hint - you are probably supposed to picture it's extent in a line of sight to you and assume the actual brightness change is instantaneous an comes from the full extent of the source.
  4. Nov 24, 2009 #3

    I see, so are we assuming that it can only extend to a maximum size of 4 light months?
    4 light months corresponds to roughly 3.1 e15 meters, which is about 1000 times the size of the S radius of the black hole.

    Does this sound right?
  5. Nov 24, 2009 #4


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    That's how I read it.
    In reality the emission is going to come from a large acreation disk around the hole so it's easy to imagine that as 1000x the Rs
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