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Math Help - Computing the mass of a neutron star from a planet's orbit

  1. #1
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    Computing the mass of a neutron star from a planet's orbit

    A small planet orbits a static neutron star in a circular orbit whose proper circumference is 6 \times 10^{11} \ \mbox{m} . The orbital period takes 200 days of the planet's proper time. Estimate the mass M of the star.

    I'm assuming I should use the far field metric

     ds^{2} = -(1 - \frac{2M}{r})dt^2 + (1 - \frac{2M}{r})(dx^2 + dy^2 + dz^2)

    but I'm not sure were to go from there.
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  2. #2
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    Re: Computing the mass of a neutron star from a planet's orbit

    The orbit of the planet will be a geodesic with respect to this metric. My guess is that calculating the geodesics and substituting in the given condtions should yield M. Also, the calculation should be easier in spherical coordinates.
    Last edited by ojones; August 13th 2012 at 03:18 PM.
    Thanks from JohnDMalcolm
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