Light freezes at the edge of the abyss: that's what the event horizon of an ordinary black hole looks like. But at the center of this abyss lurks a singularity, a point where the laws of physics break down. What if, instead of a point, there were a hard shell?
Such objects are called gravitational vacuum stars, or gravastars. In the new study, scientists went beyond the static picture. They built a rotating gravastar model within a modified theory of gravity — one where matter and the geometry of spacetime influence each other more strongly than in Einstein's theory. It turned out that the coupling parameter significantly changes the effective potential around the object. The innermost stable circular orbit (ISCO) shifts: matter can approach closer without immediately falling onto the surface.
The authors honestly note that the calculations do not yet include complex feedback from radiation pressure. But it is already clear: if astronomers see a light-filled central region where total darkness was expected, it could point to a gravastar. Not a singularity, but a hard shell in which a star is clad.
The term "gravastar" is a portmanteau of gravitational vacuum star. The model was first proposed in 2001 as an alternative to black holes, where instead of an event horizon, a phase of "gravitational Bose–Einstein condensate" emerges.
In Alastair Reynolds's novel "Revelation Space," objects resembling gravastars appear: exotic structures that hide an internal singularity behind a physical barrier.