= Static spherical Komar mass in reciprocal radial gauge
{title2=$M_K(r)=R(r)^2f'(r)/(2G)$}
For $ds^2=-f(r)dt^2+dr^2/f(r)+R(r)^2d\Omega^2$ and $K=\partial_t$ normalized at infinity, the <Komar mass> on a round sphere is $R^2f'/(2G)$. The future unit normal to a static slice is $f^{-1/2}K$, and the outward unit radial normal is $f^{1/2}\partial_r$; their contraction with $\nabla_aK_b$ gives $f'/2$, whose integral over the sphere yields the formula. The asymptotic mass is its limit at infinity. In the presence of matter, the finite-radius integral need not be constant.
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