Black-hole spectroscopy: Time/Sky-marginalisation and exotic compact objects

Black-hole spectroscopy studies the characteristic gravitational-wave emission of a perturbed black hole such as resulting from a binary merger. Measuring multiple modes of this emission-spectrum facilitates tests of general relativity's predictions for black holes, with related searches for signatures of alternative exotic compact objects revealed in altered or additional post-merger signals.

Most such studies assume a fixed arrival time and sky-location for the signal, yet the results are sensitive to the post-merger analysis start time, affected by the uncertainty in these parameters' measurement. Employing a new method to marginalise over this uncertainty, we analyse observations suitable for spectroscopic tests and measure the significance of multimode detections, emphasising those where spectroscopy has previously been performed.

Signatures of exotic compact objects can be revealed through methods derived from those of spectroscopy. We present improved and extended constraints on properties of several proposed alternatives to black holes of general relativity by analysing available gravitational-wave data and predict future instruments' prospects. This includes scalar/vector-fields near black holes; long-lived modes from classes of horizonless compact objects, yielding strict bounds on their space-time geometry; and oscillation modes in dense-fluid compact objects sourcing gravitational waves, providing insight into matter properties above neutron-star densities.