# Kerr Metric in Orthogonal form

I've seen the Kerr metric usually presented in the Boyer-Lindquist coordinates where there is a cross term in the $d\phi$ and $dt$ term. I've done a good bit of searching and cannot find any coordinates which express the Kerr metric in an orthogonal fashion. Is there ANY choice of coordinates that eliminates all cross terms/off-diagonal terms for the Kerr metric?

If not, is it just a fact that you can never find such a coordinate transformation because of the inherent geometry of the Kerr space-time?

-
No. No such coordinate system exists $globally$. The cross-term in the Kerr metric describes a physically important property of the Kerr metric - that it is not static. In particular, the solution is not symmetric under $t \to - t$ (which it would be if you could find a diagonal coordinate system). –  Prahar May 23 at 12:29