Universal Counting of Black Hole Entropy by Strings on the Stretched Horizon

TL;DR

This paper demonstrates that the entropy of any black object can be universally explained as the entropy of a highly excited string on the stretched horizon, linking black hole thermodynamics to string theory.

Contribution

It introduces a universal framework connecting black hole entropy to string states on the stretched horizon, applicable across various dimensions and black hole types.

Findings

Black hole entropy corresponds to string entropy on the stretched horizon.

Hawking temperature matches the Hagedorn temperature of the string.

Extremal and near-extremal entropies are smoothly connected.

Abstract

We show that the entropy of any black object in any dimension can be understood as the entropy of a highly excited string on the stretched horizon. The string has a gravitationally renormalized tension due to the large redshift near the horizon. The Hawking temperature is given by the Hagedorn temperature of the string. As examples, we consider black holes with one (black p-branes) or two charges, Reissner-Nordstrom black holes and the BTZ black hole in addition to Schwarzschild black holes. We show that the vanishing and nonvanishing extremal entropies can be obtained as smooth limits of the near-extreme cases.