Optical reference geometry of Kerr-Newman spacetimes

Revised and extended version Abstract. Properties of the optical reference geometry related to Kerr–Newman black-hole and naked-singularity spacetimes are illustrated using embedding diagrams of their equatorial plane. It is shown that among all inertial forces defined in the framework of the optical geometry, just the centrifugal force plays a fundamental role in connection to the embedding diagrams because it changes sign at the turning points of the diagrams. The embedding diagrams do not cover the stationary part of the Kerr–Newman spacetimes completely. Hence, the limits of embeddability are given, and it is established which of the photon circular orbits hosted the by Kerr–Newman spacetimes appear in the embeddable regions. a Corresponding author:

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