Degenerate Killing horizon
= Degenerate Killing horizon
{title2=$\kappa=0$}
A <degenerate Killing horizon> has zero <surface gravity>. In the radial quotient of an <extremal black hole>, a double horizon root produces a pole in the <tortoise coordinate> rather than the logarithm of a simple root. Such a horizon has no bifurcation surface of the usual nondegenerate type.