Black holes and black hole thermodynamics without event horizons

TL;DR

This paper explores defining black holes without event horizons, focusing on thermodynamics and trapping horizons, suggesting a potentially more practical and local approach to black hole physics.

Contribution

It demonstrates that black hole thermodynamics and Hawking radiation can be understood using trapping horizons instead of event horizons, challenging traditional definitions.

Findings

Black hole thermodynamics applies to trapping horizons.

Hawking radiation can originate from trapping horizons.

Trapping horizons offer a local alternative to event horizons.

Abstract

We investigate whether black holes can be defined without using event horizons. In particular we focus on the thermodynamic properties of event horizons and the alternative, locally defined horizons. We discuss the assumptions and limitations of the proofs of the zeroth, first and second laws of black hole mechanics for both event horizons and trapping horizons. This leads to the possibility that black holes may be more usefully defined in terms of trapping horizons. We also show how Hawking radiation can also be seen to arise from trapping horizons and discuss which horizon area should be associated with the gravitational entropy.