Matter and forces near physical black holes

TL;DR

This paper explores the formation, disappearance, and properties of regular spherically symmetric black holes in semiclassical gravity, emphasizing the necessity of violating the null energy condition and analyzing particle trajectories and tidal forces near horizons.

Contribution

It provides a detailed analysis of the energy-momentum tensor near apparent horizons and the conditions for black hole evolution in finite time, highlighting the role of NEC violation.

Findings

Escape from black holes occurs only on ingoing trajectories.

Tidal forces are finite at the apparent horizon for geodesic observers.

NEC violation is essential for black hole formation and disappearance.

Abstract

We describe general features of formation and disappearance of regular spherically symmetric black holes in semiclassical gravity. The allowed models are critically dependent on the requirement that the resulting objects evolve in finite time according to a distant observer. Violation of the null energy condition (NEC) is mandatory for this to happen, and we study the properties of the necessary energy-momentum tensor in the vicinity of the apparent horizon. In studies of the kinematics of massive test particles, it is found that the escape from a black hole is possible only on the ingoing trajectories when the particles are overtaken by the contracting outer apparent horizon. Tidal forces experienced by geodesic observers, infalling or escaping, are shown to be finite at the apparent horizon, although this is not true for nongeodesic trajectories.