Affine horizon-generator scaling
= Affine horizon-generator scaling
{title2=$\xi=\kappa\lambda k$}
If a <Killing horizon> generator $\xi$ has constant nonzero <surface gravity> $\kappa$, write $\xi=F(\lambda)k$ with $k=d/d\lambda$ affine. The equation $\nabla_\xi\xi=\kappa\xi$ implies $dF/d\lambda=\kappa$, so shifting the affine origin gives $\xi=\kappa\lambda k$.