Evanescent Black Holes

TL;DR

This paper presents an exactly solvable 2D quantum gravity model showing that collapsing matter radiates away all energy before forming a black hole, implying black holes may not exist in the quantum spectrum.

Contribution

It introduces a solvable 2D quantum gravity theory with matter, analyzing black hole formation, Hawking radiation, and backreaction, suggesting black holes evaporate completely.

Findings

Collapsing matter radiates away before horizon formation

Black holes disappear from the quantum spectrum

A unitary S-matrix including zero-energy states is proposed

Abstract

A renormalizable theory of quantum gravity coupled to a dilaton and conformal matter in two space-time dimensions is analyzed. The theory is shown to be exactly solvable classically. Included among the exact classical solutions are configurations describing the formation of a black hole by collapsing matter. The problem of Hawking radiation and backreaction of the metric is analyzed to leading order in a $1/N$ expansion, where $N$ is the number of matter fields. The results suggest that the collapsing matter radiates away all of its energy before an event horizon has a chance to form, and black holes thereby disappear from the quantum mechanical spectrum. It is argued that the matter asymptotically approaches a zero-energy ``bound state'' which can carry global quantum numbers and that a unitary $S$-matrix including such states should exist.