They may be compact objects with a physical surface and a dark-energy interior. Same silhouette from the outside. Different if you wait.
Pawel Mazur and I proposed that the end point of complete gravitational collapse is not a singularity behind an event horizon, but a gravitational vacuum condensate star — a gravastar. The object is as compact as a black hole. It has a thin quantum surface at the would-be horizon, and a non-singular de Sitter interior. The information paradox and the singularity are not puzzles to be endured. They are signs that the classical idealization went too far.
Kurzgesagt’s public telling, 2024. The papers below are the actual argument.
Gravastars can mimic the first look of a LIGO merger and an EHT shadow. They have not been confirmed by those observations. The distinction lives in the late ringdown, surface modes, and thermodynamics — a gong with echoes, not a bass drum that stops.
If successor gravitational-wave detectors see a clean Kerr ringdown, with no echoes, at signal-to-noise high enough to have seen a near-horizon surface, the thin-shell picture is in trouble. Present LVK echo searches are null. That is the honest state of the bet, not a footnote.
If you are a student who wants a problem, not a personality: start here.