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Chadrashekar limit

  1. Dec 5, 2006 #1

    quasar987

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    Chadrasekhar limit

    In my thermo text, we arrived at an estimate of the chandrasekhar limit using the assumptions T=0, uniform mass density and.... p>>mc.

    I can maaaaaybe accept that in the context of a very rough approximation, but then the text says, "A more realistic calculation, which does not suppose a uniform density, gives [itex]M_C=1.4 M_{\bigodot}[/itex]". Thats means that in their so-called more realistic calculation, they still assume the unphysical p>>mc.

    That someone explain that?
     
    Last edited: Dec 5, 2006
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  3. Dec 6, 2006 #2

    SpaceTiger

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    If the momenta were not much greater than mc throughout much of the star, then the star would be sub-Chandrasekhar, practically by definition. Another way of thinking of the Chandrasekhar mass is the limit of relativistic degeneracy for a self-gravitating, electron-degenerate object.
     
  4. Dec 6, 2006 #3

    quasar987

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    Oh wait a sec. My problem is that I was thinking classically about momentum. p>>mc does not imply v>>c. So there is nothing unphysical about p>>mc.
     
  5. Dec 6, 2006 #4

    George Jones

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    Remember, in relativity, the spatial part of momentum is given by

    [tex]
    p = \frac{mv}{\sqrt{1 - \frac{v^2}{c^2}}},
    [/tex]

    not by the Newtonian expression [itex]p = mv[/itex].

    Thu,s [itex]p >> mc[/itex] when [itex]v >> c/\sqrt{2}[/itex], so [itex]v > c[/itex] is not needed.

    Edit: While I was typing, you saw the light. :smile:
     
    Last edited: Dec 6, 2006
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