The work performed falls intro three broad categories:
Black hole spectroscopy. We have extracted nonlinear modes from numerical relativity data,
providing convincing evidence for their existence. We have put on a firm ground the spectral
instability of the fundamental mode of black holes, but we have also made extensive numerical
simulations that indicate that such instabilities will not affect significantly the time domain
waveforms on timescales relevant for current detectors. We have developed new analysis tools to
dig out ringdown modes from data.
Dynamical strong field gravity: We have pioneered studies of gravitational-wave emission in
the presence of matter, by using black hole perturbation theory in the context of extreme-mass-
ratio inspirals. We have worked on analysing the dynamics of inner horizons and extremal
horizons in semiclassical gravity. We have also worked on classical field perturbations of black
holes and compact stellar objects, involving spectrum, pseudospectrum and scattering
calculations. We have provided the formalism to handle stellar physics with relativistic
dissipation mechanisms.
We identified turbulent flows in accretion disks around black holes as significant sources of
gravitational waves and of excitation of the characteristic modes of black holes. Using General
Relativistic Magneto-Hydrodynamic simulations, we predicted a stochastic background of
gravitational waves from supermassive black holes might be detectable by future microhertz
detectors.
In the context of dark matter physics and of new fundamental fields, we showed how accretion
disks may dramatically affect the gravitational wave signals of black hole binaries in the inspiral
and ringdown phases, inducing non- vanishing love numbers and echoes. We developed a novel
framework for modeling ultralight bosons, advancing astrophysical studies.
