Black-hole microstate spectroscopy

Abstract: The quasinormal-mode spectrum of a horizonless compact object can differ significantly from that of the corresponding classical black hole. However, the time response is initially very similar if the object is sufficiently compact. A generic smoking gun of the absence of a classical horizon is the presence of echoes in the late-time ringdown. The echo delay time and morphology depend crucially on the properties of the object down to its potential well. Most of the echo analyses so far have considered toy or phenomenological models. I will present recent results on the ringdown phenomenology for a class of multicenter geometries describing the microstates of a static BPS black hole in N=2 supergravity, unveiling the whole ringdown phenomenology studied in recent years for exotic compact objects albeit in much more complicated settings in which the ringing object has a complex multipolar structure. The numerical method is based on numerical-relativity simulations of a test scalar field propagating on these geometries and can be applied to any stationary microstate, including non-BPS ones. These results provide the first numerical evidence for the dynamical linear stability of fuzzballs, and pave the way for an accurate discrimination between fuzzballs and black holes using gravitational-wave spectroscopy.