# Moving black holes: energy extraction, absorption cross-section and the ring of fire

## TL;DR

This paper investigates how moving black holes interact with plane waves, revealing energy transfer from black holes to waves, negative absorption cross-sections, and a bright ring phenomenon around relativistically moving black holes.

## Contribution

It introduces the concept of negative absorption cross-section for moving black holes and describes the formation of a bright ring around relativistic black holes.

## Key findings

- Black holes transfer energy to incident waves.
- Moving black holes have negative absorption cross-sections.
- Relativistic black holes appear surrounded by a bright ring.

## Abstract

We consider the interaction between a plane wave and a (counter-moving) black hole. We show that energy is transferred from the black hole to the wave, giving rise to a negative absorption cross-section. Moving black holes absorb radiation and deposit energy in external radiation. Due to this effect, a black hole hole of mass M moving at relativistic speeds in a cold medium will appear to be surrounded by a bright "ring" of diameter 3\sqrt{3}GM/c^2 and thickness GM/c^2.