Gravitational waves from the coalescence of compact binaries provide a unique opportunity to test gravity in the strong field regime. In particular, the postmerger phase of the gravitational signal is a proxy for the nature of the remnant.
This is of particular interest in view of some quantum-gravity models which predict the existence of horizonless dark compact objects that overcome the paradoxes associated to black holes. Such dark compact objects can emit a modified gravitational wave signal with respect to the black hole case and late-time gravitational wave echoes as characteristic fingerprints.
In this talk, I develop a generic framework to the study of the ringdown of dark compact objects and provide a gravitational-wave template for the echo signal. Finally, I assess the detectability of dark compact objects with current and future gravitational-wave detectors.