Thermodynamic acceptability of spherically symmetric perfect-fluid solutions in general relativity
Static spherically symmetric perfect-fluid solutions of Einstein's equations play a central role in relativistic astrophysics and stellar structure theory. While many exact solutions satisfy Einstein's equations mathematically, only a limited subset satisfies physically acceptable conditions such as regularity, positivity of matter variables, and causal sound propagation. In this work, the classical concept of physical acceptability is extended to include thermodynamic considerations. Using relativistic equilibrium thermodynamics, entropy functionals, and the Tolman temperature relation, we formulate a set of thermodynamic acceptability conditions for relativistic stellar models. The Tolman IV solution is analyzed as an explicit example. We show that this solution admits a finite and positive equilibrium entropy functional consistent with the Tolman equilibrium condition. This analysis suggests that thermodynamic consistency provides a natural extension of the Delgaty-Lake acceptability program and may constitute an essential criterion in the classification of relativistic interior solutions.