Periodic Reporting for period 1 - Gravitas (Black holes: gravitational engines of discovery)
Reporting period: 2022-12-01 to 2025-05-31
Gravitational-wave astronomy opened a new window to a previously invisible universe. Driven by this momentous event, gravitational physics is experiencing a revolution, and is an exciting line of research with an immense discovery potential. The project proposes to provide new and clear tests of gravity in the strong field regime, of black hole physics and on the existence of new fundamental fields in our universe, and help to constrain dark matter structures with gravitational-wave astronomy.
We will lay down a precise roadmap for black hole spectroscopy, including a characterization of nonlinear ringdown and late time dynamics of black holes. We will quantify the evidence for horizons in the cosmos, using electromagnetic and gravitational-wave observations. The project will establish a team, leading efforts to understand lensed gravitational-wave events and its cosmological implications. This coordinated program will study and test the strong-field regime of gravity and the matter content of our universe. The proposed program will significantly advance our knowledge of Einstein’s field equations and their role in foundational questions, including the fate and resolution of spacetime singularities. The coming years will be crucial to determine new directions.
We will lay down a precise roadmap for black hole spectroscopy, including a characterization of nonlinear ringdown and late time dynamics of black holes. We will quantify the evidence for horizons in the cosmos, using electromagnetic and gravitational-wave observations. The project will establish a team, leading efforts to understand lensed gravitational-wave events and its cosmological implications. This coordinated program will study and test the strong-field regime of gravity and the matter content of our universe. The proposed program will significantly advance our knowledge of Einstein’s field equations and their role in foundational questions, including the fate and resolution of spacetime singularities. The coming years will be crucial to determine new directions.
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.
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.
In 2023, we re-designed black hole spectroscopy, with three seminal results, now being explored
by the community: i. We showed that black hole ringdown carries imprints of the nonlinearities
of Einstein’s equations; ii. The black hole spectrum is unstable to external effects and iii.
Evidence for overtones in gravitational-wave data will likely need to wait for future detectors.
These results are re-shaping the field and community, and even though published only last year,
they are all top-cited works already. My group convened a focused meeting with all experts in
August 2024 at the Black Diamond, a legendary venue in Copenhagen, to discuss the way
forward.
by the community: i. We showed that black hole ringdown carries imprints of the nonlinearities
of Einstein’s equations; ii. The black hole spectrum is unstable to external effects and iii.
Evidence for overtones in gravitational-wave data will likely need to wait for future detectors.
These results are re-shaping the field and community, and even though published only last year,
they are all top-cited works already. My group convened a focused meeting with all experts in
August 2024 at the Black Diamond, a legendary venue in Copenhagen, to discuss the way
forward.