Equatorial photon motion in the Kerr-Newman spacetimes with a non-zero cosmological constant

Understand

Discussion of the equatorial photon motion in Kerr-Newman black-hole and naked-singularity spacetimes with a non-zero cosmological constant is presented.

• Both repulsive and attractive cosmological constants are considered.
• Circular photon orbits are determined, and their stability is established.
• The spacetimes are divided into separated classes according to the properties of the `effective potential'.