Light rings of stationary spacetimes

We present a novel theorem regarding light rings in a stationary spacetime with an ergoregion. We prove that any stationary, axisymmetric, and asymptotically flat spacetime in 1+3 dimensions with an ergoregion must have at least one light ring outside the ergoregion. A possible extension of the proof for asymptotically de Sitter and anti-de Sitter spherically symmetric black holes is also discussed.