arXiv subjects

Giuseppe Ficarra

Publications and source records attributed to Giuseppe Ficarra.

10 recordsLinked to original sources

arXiv2026

Ringdown and lensing of triple systems

Triple systems have progressively been recognized as ubiquitous in our Universe and provide a good testing ground for wave generation and propagation in nontrivial environments. We study the dynamics of triple systems in a fully nonlinear setting. In particular, we analyze numerical relativity simulations of head-on collisions of black holes in the presence of a companion. We show evidence for Doppler and gravitational redshift in the ringdown, and clear signs of amplification by lensing. In certain cases, we also show the appearance of a second image, with hints of resonant mode excitation. Our results pave the way for the understanding of mergers in the vicinity of massive companions. Even in extreme setups we do not find collapse to black holes from lensed gravitational radiation.

gr-qc↗

arXiv2026

The Fifth RIT Catalog of Binary Black Hole Simulations: Multiple-Resolution Studies of Eccentric Orbits

This fifth release of the RIT public catalog of numerical relativity binary black hole waveforms http://ccrg.rit.edu/~RITCatalog introduces an additional 248 configurations, prioritizing 197 newly simulated eccentric orbits. This update brings the catalog to a total of 2129 cases. All waveforms are corrected for center-of-mass drift and extrapolated to future null infinity. To rigorously estimate waveform errors, we conduct multiple-resolution convergence studies on 10 eccentric simulations (up to 33 orbits to merger) using three global resolutions increasing by factors of 1.2, plus a comprehensive six-resolution study for a single 18-orbit configuration. We evaluate waveform accuracy by computing mismatches against theoretical infinite-resolution extrapolations. Additionally, we analyze the convergence properties of key physical observables: merger times, number of orbits, final masses, final spins, recoil velocities, and the peak amplitude, frequency, and luminosity of the gravitational radiation.

gr-qc↗

arXiv2026

Parameter Estimation with Targeted Eccentric Numerical-Relativity Simulations for GW200208_22 and GW190620

We have analyzed LVK gravitational wave events that show some evidence of eccentricity from TEOBResumS modeling parameter estimations and have confronted them independently with full numerical generated waveforms from our bank of nearly two thousand simulations of binary black holes. We have used RIFT for Bayesian parameter estimation and found that GW200208_22 KDE estimates favor eccentricities $e_{20} = 0.198_{-0.180}^{+0.119}$ upon entering the LVK band at $\sim20$Hz within a $90\%$ confidence interval. Within this event analysis we employed 42 new targeted full numerical relativity simulations and we have thus found a top improved likelihood $\ln\mathcal{L}$ matching waveform, compared to model-based analysis, with an estimated eccentricity at 20Hz, $e_{20}=0.200$, thus reinforcing the eccentric hypothesis of the binary. We have also used our full bank of numerical waveforms on GW190620 finding that the KDE estimate favors eccentricities at 10 Hz in $e_{10}=0.190_{-0.186}^{+0.046}$. New specifically targeted simulations will be required to narrow these eccentricity ranges.

gr-qc↗

arXiv2026

The Role of Inhomogeneities in the Turbulent Accretion of Black Holes

Observations of supermassive black holes by the Event Horizon Telescope reveal significant inhomogeneities, most likely related to density and magnetic field perturbations. To model these features, we conduct high-resolution 2D general-relativistic magnetohydrodynamics (GRMHD) simulations of a Fishbone-Moncrief torus around a Kerr black hole using the Black Hole Accretion Code $\texttt{BHAC}$. We compare unperturbed accretion with a case featuring plasma density bubbles with pressure balanced magnetic islands of different amplitudes. Power spectrum analysis of accretion time series, performed via the Blackman-Tukey method, shows that the perturbed case exhibits (1) steeper spectral indices compared to the unperturbed case, deviating from the characteristic $1/ω$ noise spectrum, and (2) increased correlation times, providing evidence for absorption of macro-structures at the event horizon. Spatial auto-correlation analysis of near-horizon turbulence confirms larger energy-containing coherent structures in the perturbed case altering the accretion rate. These results provide new insights for interpreting observations of supermassive black hole environments, where near-horizon turbulence may play a key role in the accretion process.

gr-qc↗

arXiv2025

Measuring the properties of homogeneous turbulence in curved spacetimes

Turbulence in curved spacetimes in general, and in the vicinity of black holes (BHs) in particular, represents a poorly understood phenomenon that is often analysed employing techniques developed for flat spacetimes. We here propose a novel approach to study turbulence in strong gravitational fields that is based on the computation of structure functions on generic manifolds and is thus applicable to arbitrary curved spacetimes. In particular, we introduce, for the first time, a formalism to compute the characteristic properties of turbulence, such as the second-order structure function or the power spectral density, in terms of proper lengths and volumes and not in terms of coordinate lengths and volumes, as customarily done. By applying the new approach to the turbulent rest-mass density field from simulations of magnetised disc accretion onto a Kerr BH, we inspect in a rigorous way turbulence in regions close to the event horizon, but also in the disc, the wind, and in the jet. We demonstrate that the new approach can capture the typical behavior of an inertial-range cascade and that differences up to $40-80\%$ emerge in the vicinity of the event horizon with respect to the standard flat-spacetime approach. While these differences become smaller at larger distances, our study highlights that special care needs to be paid when analysing turbulence in strongly curved spacetimes.

gr-qc↗

arXiv2025

Dephasing in binary black hole mergers surrounded by scalar wave dark matter clouds

Scalar fields of masses between $10^{-21}\rm{eV}/c^2$ and $10^{-11} \rm{eV}/c^2$ can exhibit enhanced gravitational interactions with black holes, and form scalar clouds around them. Such a cloud modifies the dynamics of a coalescing black-hole binary, and the resulting gravitational waves may provide a new channel to detect light scalar fields, such as axion-like particles or wave-like dark matter candidates. In this work we simulate a series of black-hole mergers with mass ratios $q=1$ and $q=1/2$, immersed in an scalar field overdensity with masses in the range $Mμ_{\rm{S}} \in[0,1.0]$. To do so, we implemented a constraint-satisfying initial data solver based on the puncture method, we improved the accuracy of our open-source software Canuda to eighth order finite differences, and we reduced the initial orbital eccentricity. We investigate the impact of the scalar mass on the gravitational and scalar radiation. We find that binaries can undergo a delayed or an accelerated merger with respect to the vacuum. Our study highlights the challenge and importance of accurately modeling black-hole binaries in dark matter environments.

gr-qc↗

arXiv2025

Eccentric Binary Black Hole Simulations with Numerical Relativity

We perform a systematic study of eccentric orbiting nonspinning black hole binaries. We first make a technical study of the optimal full numerical techniques to apply to these studies. We choose different gauge parameters and Courant factors, $c=dx/dt$, and find an optimal value for it of 0.45. We also find the grid structure and global resolution that optimize accuracy and speed of current computational resources. With these choices we perform a study of the merger times $t_m$ as a function of eccentricity for configurations with comparable orbital energy content and find that they are well represented by the post-Newtonian factor $F(e)=(1+73e^2/24+37e^4/96)/(1-e^2)^{7/2}$ when merger times are normalized to their quasicircular values, i.e. $t_m(e)/t_m\approx F(e)$. We then perform a systematic coverage of five small-medium eccentricities up to $e\sim0.45$ and six mass ratios up to 8.5:1 producing a total of 30 simulations covering up to 25 orbits to merger to further model merger times and as a seed to a forthcoming new systematic catalog of gravitational waveforms from eccentric binary black holes to directly perform parameter estimations of gravitational waves events.

gr-qc↗

arXiv2024

Close Encounter of Three Black Holes III

We revisit the three black hole scenario with numerical relativity techniques to study hierarchical configurations where the inner binary contains highly spinning black holes. We find that the merger time of the binary gets a delay (with a number of orbits to merger increase), depending strongly with the distance to the orbiting third hole $D$ as $\sim1/D^{1.6\pm0.1}$. Notably, a different dependence from what we had found in the nonspinning case, $\sim1/D^{2.5}$. We interpret this effect as mostly due to a spin-orbit coupling between the third hole and the closest member of the binary in the successive approaches. This lead us next to study scattering configurations of the third hole with the binary in order to evaluate the extent of this ``sudden'' interactions, finding also a correlation of the delay in merger times with the closest distance, even for the nonspinning cases. We then explore the mass ratio dependence of the triple system by modeling binaries orbiting a larger black hole bearing masses ratios 8:1:1 and 18:1:1 in co-orbiting or counter-orbiting configurations, finding merger times increasing with increasing mass ratios and for the counter-orbiting cases.

gr-qc↗

arXiv2021

Scalar field dynamics around black holes: superradiant instabilities and binary evolution

In classical general relativity astrophysical black holes can be affected by the superradiant instability when gravity is minimally coupled to a light bosonic field. The majority of phenomenological studies have focused on the idealized case in which the black hole is initially surrounded by a single mode superradiant seed. By studying the evolution of a scalar field with multiple modes initial data in a quasiadiabatic approximation, we show that the dynamics is more involved and depend on the initial seed energy and the amplitude ratio between the modes. We also present preliminary results of the dynamical evolution of a massive scalar field around a Newtonian and a fully relativistic, black hole binary.

gr-qc↗

arXiv2019

Impact of multiple modes on the black-hole superradiant instability

Ultralight bosonic fields in the mass range $\sim (10^{-20}-10^{-11})\,{\rm eV}$ can trigger a superradiant instability that extracts energy and angular momentum from an astrophysical black hole with mass $M\sim(5,10^{10})M_\odot$, forming a nonspherical, rotating condensate around it. So far, most studies of the evolution and end-state of the instability have been limited to initial data containing only the fastest growing superradiant mode. By studying the evolution of multimode data in a quasi-adiabatic approximation, we show that the dynamics is much richer and depend strongly on the energy of the seed, on the relative amplitude between modes, and on the gravitational coupling. If the seed energy is a few percent of the black-hole mass, a black hole surrounded by a mixture of superradiant and nonsuperradiant modes with comparable amplitudes might not undergo a superradiant unstable phase, depending on the value of the boson mass. If the seed energy is smaller, as in the case of an instability triggered by quantum fluctuations, the effect of nonsuperradiant modes is negligible. We discuss the implications of these findings for current constraints on ultralight fields with electromagnetic and gravitational-wave observations.

gr-qc↗