Extremal Black holes and the limits of the third law

TL;DR

This paper discusses the nature of extremal black holes and the implications for the third law of black hole thermodynamics, considering quantum field theory results and the need for a full semiclassical approach.

Contribution

It examines whether extremal black holes can be considered thermal objects and explores the necessity of revising thermodynamic laws or theories.

Findings

Extremal black holes may not be thermal objects according to quantum field theory.

The zero temperature notion for extremal black holes might be ill-defined.

Revising the third law of black hole thermodynamics could be necessary.

Abstract

Recent results of quantum field theory on a curved spacetime suggest that extremal black holes are not thermal objects and that the notion of zero temperature is ill-defined for them. If this is correct, one may have to go to a full semiclassical theory of gravity, including backreaction, in order to make sense of the third law of black hole thermodynamics. Alternatively, it is possible that we shall have to drastically revise the status of extremality in black hole thermodynamics.