From micro to macro and back: probing near-horizon quantum structures with gravitational waves

Supermassive binaries detectable by the planned space gravitational-wave interferometer LISA might allow us to distinguish black holes from ultracompact horizonless objects, even for certain models motivated by quantum-gravity considerations. We show that a measurement of a very small tidal Love number with accuracy (as achievable by detecting ‘golden binaries’) may also allow us to distinguish between different models of these exotic compact objects, even when taking into account an intrinsic uncertainty in the object radius putatively due to quantum mechanics. We argue that there is no conceptual obstacle in performing these measurements, the main challenge remains the detectability of small tidal effects and an accurate waveform modelling.