Environment-induced topological reconstruction of black-hole thermodynamics

Abstract

Thermodynamic topology describes black-hole (BH) equilibria as zeros, or defects, of a vector field built from the off-shell free energy. Studies with surrounding matter find that the topological class is unchanged, but not how the matter's spatial distribution affects individual equilibria. We ask whether the position of a localized environment can reorganize these equilibria at fixed total topological number. We model the environment as a radially localized energy bump peaked at $a_m$ and add its exterior energy to the generalized off-shell free energy. As $a_m$ varies, defects migrate and are created or annihilated in opposite-charge pairs, a process we call topological reconstruction. It changes the number and stability of equilibrium branches but preserves the total topological number, provided no zero crosses the boundary of the physical domain. We find this in Schwarzschild, Schwarzschild-AdS, Reissner-Nordström, and Reissner-Nordström-AdS BHs, with critical positions and required strength that depend on the background. In our examples, the required environmental energy ranges from below $1\%$ of the BH mass to a value comparable to it. The model is an effective fixed-background description without backreaction. Within it, the total topological number cannot capture the environmental response; local defects must be tracked.