Extremal black holes have external light rings

Abstract

It is proved that spherically symmetric extermal black holes possess at least one external light ring. Our remarkably compact proof is based on the dominant energy condition which characterizes the external matter fields in the non-vacuum extremal black-hole spacetimes.

9 pages

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Cited by in corpus (5)

• Static spheres around spherically symmetric black hole spacetime
• The existence of null circular geodesics outside extremal spherically symmetric asymptotically flat hairy black holes
• Can light-rings self-gravitate?
• Bounds for Lyapunov exponent of circular light orbits in black holes
• Characterisation of circular light rays in a plasma