Title: Exotic compact objects and how to quench their ergoregion instability
Speaker: Elisa Maggio (Sheffield University)
Gravitational-wave astronomy can give us access to structure of black holes, potentially probing microscopic corrections at the horizon scale. Some quantum-gravity models of exotic compact objects replace the event horizon by a reflective surface. Objects with these properties are prone to the so-called ergoregion instability when spinning sufficiently fast.
I will show that the ergoregion instability generically affects exotic compact objects with a perfectly reflecting surface, and might have a crucial impact on the phenomenology of these objects. On the other hand, I will describe an effect that can prevent the ergoregion instability from developing. A partial absorption at the surface as small as 0.4% is sufficient to quench the instability completely. This finding has important consequences for the viability of exotic compact objects and it suggests that exotic compact objects are not necessarily ruled out by the ergoregion instability.