Uniqueness of stationary axisymmetric type D black holes with non-aligned electromagnetic field

Abstract

We demonstrate the uniqueness of the spacetimes recently found by us in [H. Ovcharenko and J. Podolsky, Phys. Rev. D 112 (2025) 064076]. First, we prove that the conformal-to-Carter metric ansatz we used therein is the only possible for stationary axisymmetric geometries that are of Weyl type D, with geodesic and shear-free principal null directions (PNDs) which are orthogonal to polar directions, and whose specific 1-form $\theta$ is closed. Because this result is general, without employing any field equations, such conformal-to-Carter metric may find interesting applications also in various alternative theories of gravity. Then, we show that in the Einstein-Maxwell theory the only non-trivial electrovacuum solution for the conformal-to-Carter metric with the fully non-aligned and non-null electromagnetic field is the Ovcharenko-Podolsky class found in 2025. Complementarily, the only solution with the double-aligned and non-null electromagnetic field is the Pleba\'nski-Demia\'nski class found in 1976.