= Kerr stationary-limit surface is generically timelike
{c}
{title2=$g^{ab}\partial_as\partial_bs=(\Delta+r_e'(\theta)^2)/\Sigma>0$}
For subextreme <Kerr spacetime>, the outer stationary-limit surface is $s=r-r_e(\theta)=0$, where $r_e=M+\sqrt{M^2-a^2\cos^2\theta}$. Away from the rotation axis, $r_e>r_+$ and $\Delta(r_e)=a^2\sin^2\theta>0$. Its normal is therefore spacelike and the surface timelike. Although the stationary <Killing vector field> has zero norm on it, it is not normal to it, and the surface is not a <Killing horizon>. The actual outer Killing horizon is $r=r_+$, generated by $K+\Omega_H\Phi$.
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