I-Q relations and radial stability of ultracompact Schwarzschild stars and their approach to the ‘black-hole’ limit

Exotic compact objects (ECOs), or black-holes ‘mimickers’, have re-
ceived considerable interest after the event GW150914. One of these
black-hole mimickers, is the gravastar proposed by Mazur and Mottola.
In this talk I will review the recently discovered connection between the
Schwarzschild interior solution, or ‘Schwarzschild star’, and gravastars.
Mazur and Mottola (2015) have shown that for non-rotating Schwarzschild
stars the limiting configuration when R = Rs = 2M is a gravastar. This
object is described by the exterior Schwarzschild metric in the region
r > Rs, a modified de Sitter metric in the interior r < Rs and a sur-
face tension near Rs. Recently, I extended this model to slow rotation
using the structure equations derived by Hartle. I will discuss these re-
sults and their relevance in the context of the I-Q relations. Additionally
I will discuss recent results on the radial stability of the ultracompact
Schwarzschild star.