Surface gravity of a static spherical horizon
= Surface gravity of a static spherical horizon
{title2=$\kappa=\tfrac12\sqrt{A'(r_+)B'(r_+)}$}
For a <static spacetime> with $g_{tt}=-A(r)$, $g_{rr}=1/B(r)$ and simple simultaneous horizon zeros, the squared <surface gravity> of $\partial_t$ is $\lim BA'^2/(4A)=A'(r_+)B'(r_+)/4$. Choose the positive value for the outer horizon. A rescaling of the time generator rescales its <surface gravity>.