The Stress-Energy of Gravitational Vacuum Condensate Stars

I discuss candidates for the physical nature of the stress-energy that produces a gravitational vacuum condensate star: a stable, non-singular alternative to black holes also known as a gravastar. Arguments relying on classical energy conditions have been made for the existence of singular “black holes” for over half a century. Despite this, questions about the singular solution remain, such as the nature of a black hole’s entropy. These questions, combined with the discovery of dark energy, which violates the strong energy condition (SEC), have motivated interest in alternatives to black holes. A gravastar, characterized by an SEC-violating de Sitter interior with a sharp boundary layer at the Schwarzschild radius, is one of these alternatives. While it has been known for some time that gravastars are viable solutions to Einstein’s equations, the nature of the stress-energy that could give rise to them is still unclear. I discuss how the gravitational trace anomaly may generate the boundary layer of a gravastar. I then demonstrate how a cosmological constant can be written as the Hodge dual of a four-form field. This constant is the Euler-Gauss-Bonnet term, which becomes dynamical at the boundary layer, allowing for a de Sitter interior of a gravastar with a vanishing cosmological constant in the exterior.