Thermodynamic motivations of spherically symmetric static metrics

TL;DR

This paper explores the thermodynamic properties of spherically symmetric static metrics, deriving conditions for event horizons and analyzing the relationship between different mass definitions and surface gravity within Einstein's theory.

Contribution

It introduces a novel approach linking thermodynamics with metric functions using the Gong-Wang mass and generalizes thermodynamic laws to null hypersurfaces, revealing new insights into black hole horizons.

Findings

Null hypersurface identified as an event horizon.

Energy-momentum tensor matches polytropic black hole in AdS.

Relationship between Gong-Wang and Misner-Sharp masses analyzed.

Abstract

Bearing the thermodynamic arguments together with the two definitions of mass in mind, we try to find metrics with spherical symmetry. We consider the adiabatic condition along with the Gong-Wang mass, and evaluate the $g_{rr}$ element which points to a null hypersurface. In addition, we generalize the thermodynamics laws to this hypersurface to find its temperature and thus the corresponding surface gravity which enables us to get a relation for the $g_{tt}$ element. Moreover, we investigate the mathematical and physical properties of the discovered metric in the Einstein relativity framework which shows that the primary mentioned null hypersurface is an event horizon. The obtained energy-momentum tensor equals the energy-momentum tensor of a polytropic black hole embedded into an anti-de Sitter background. We also show that if one considers the Misner-Sharp mass in the calculations, the Schwarzschild metric will be got. The relationship between the two mass definitions in each metric is studied. The results of considering the geometrical surface gravity are also addressed. Our investigation shows that the geometrical surface gravity's definition is not always compatible with the validity of the first law of thermodynamics on the horizons of spherically symmetric static metrics.