Black holes and the nature of the event horizon

TL;DR

This paper discusses the nature of black hole event horizons, their singularities, and how gravitational wave observations can shed light on their physics, especially during black hole mergers.

Contribution

It highlights the potential of gravitational wave studies to improve understanding of the event horizon and the possible absence of singularities in quantum gravity.

Findings

Singularities at the event horizon and center reflect collapse phenomena.

Gravitational wave observations can help clarify event horizon physics.

Ringdown quasi-normal modes are key to understanding black hole remnants.

Abstract

The problem of the event horizon in relativistic gravity is discussed. Singular solutions in general relativity are well known. The Schwarschild metric of a spherical mass is singular at zero ($r = 0$) and at the event horizon ($r = r_g$). Both features reflect the existence of the phenomenon of collapse in general relativity for compact masses exceeding $3M_{\odot }$. A material particle crossing the event horizon falls into a central singularity according to the classical theory of general relativity. In the quantum theory of gravity, there may be no central singularity. The physics of the event horizon is currently being refined. A promising technique is the study of gravitational waves (GW) accompanying the merger of binary black holes at the ringdown stage. GW observations of quasi-normal modes of the newly formed super dense remnant will help clarify the physics of the event horizon.