Nonaxisymmetric instability and fragmentation of general relativistic quasitoroidal stars

In a recent publication, we have demonstrated that differentially rotating stars admit new channels of black hole formation via fragmentation instabilities. Since a higher order instability of this kind could potentially transform a differentially rotating supermassive star into a multiple black hole system embedded in a massive accretion disk, we investigate the dependence of the instability on parameters of the equilibrium model. We find that many of the models constructed exhibit nonaxisymmetric instabilities with corotation points, even for low values of T/|W|, which lead to a fission of the stars into one, two, or three fragments, depending on the initial perturbation. At least in the models selected here, an m=1 mode becomes unstable at lower values of T/|W|, which would seem to favor a scenario where one black hole with a massive accretion disk forms. In this case, we have gained evidence that low values of compactness of the initial model can lead to a stabilization of the resulting fragment, thus preventing black hole formation in this scenario.