Long-Term Stable Nonlinear Evolutions of Ultracompact Black-Hole Mimickers

We study the stability of ultracompact boson stars admitting light rings combining a perturbative analysis with 3+1 numerical-relativity simulations with and without symmetry assumptions. We observe excellent agreement between all perturbative and numerical results, which uniformly support the hypothesis that this family of black-hole mimickers is separated into stable and unstable branches by extremal-mass configurations. This separation includes, in particular, thin-shell boson stars with light rings located on the stable branch, which we conclude to represent long-term stable black-hole mimickers.