Mode stability of a near-extremal Kerr superspinar

We study here the quasi-normal mode stability of a near-extremal Kerr superspinar, an exotic spinning compact object that exceeds the Kerr bound, under gravitational perturbations. Despite previous beliefs that these objects would be mode unstable, we show by analytically treating the Teukolsky equations that these objects are in fact mode stable under almost all (barring a zero-measure set) boundary conditions.