arXiv subjects

Giacomo Fedrigo

Publications and source records attributed to Giacomo Fedrigo.

3 recordsLinked to original sources

arXiv2026

Spacetime in motion: an evolving relativistic binary black hole metric for GIZMO

The last evolutionary stages of massive black hole binaries prior to coalescence is dominated by the emission of gravitational waves, which will be probed by the future Laser Interferometer Space Antenna. If gas is present around the two black holes, however, the associated electromagnetic emission can provide additional information about the binary properties and location before the merger event. For this reason, a proper characterisation of the electromagnetic emission during these phases is of fundamental importance, and requires a detailed description of the gas dynamics close to the event horizon of the two black holes, only achievable via numerical simulations. Within this context, we present the implementation of the Superposed Kerr-Schild dynamic metric in the relativistic scheme in the meshless code GIZMO. Our code can now simulate black hole binaries approaching merger with high computational efficiency and accuracy, taking into account relativistic effects on the gas. To validate our implementation, we perform two tests. First, we explore the case of a relativistic Bondi flow around a binary, finding very good agreement with numerical relativity simulations. Then we explore the case of an inviscid relativistic circumbinary disc, comparing our results with a similar simulation run assuming Newtonian gravity. In this second case, we find moderate differences in the mass accretion rate and in the inflow dynamics, which suggest that the presence of a non-Keplerian potential and of apsidal precession in the orbiting gas trajectories may produce stronger shocks and boost angular momentum transport in the disc. Our work highlights the importance of accounting for relativistic corrections in accretion disc simulations around black hole binaries approaching merger, even at scales much larger than those currently probed by numerical relativity simulations.

astro-ph.HE↗

arXiv2025

A general relativistic magnetohydrodynamics extension to mesh-less schemes in the code GIZMO

The profound comprehension of the evolution and phenomenology of an Active Galactic Nucleus requires an accurate exploration of the dynamics of the magnetized gaseous disk surrounding the massive black hole in the centre. Many numerical simulations have studied this environment using elaborate grid-based codes, but in recent years, new mesh-less schemes have exhibited excellent conservation properties and good accuracy at a more moderate computational cost. Still, none implement general relativistic magnetic fields, a fundamental ingredient to model an accretion disk around a massive black hole. We present here a general relativistic magnetohydrodynamics (GRMHD) scheme working within the mesh-less framework of the code \texttt{GIZMO}. We implement the hyperbolic divergence cleaning procedure, consistently extended to general relativistic effects, to keep the magnetic field divergence under safe levels. We benchmark the scheme against various relativistic magnetohydrodynamics stress tests, considering different dimensionalities and both a Minkowski or a Schwarzchild/Kerr background. To date, this is the first GRMHD scheme working in a mesh-free environment.

astro-ph.HE↗

arXiv2024

GRMHD simulations of accretion flows onto massive binary black hole mergers embedded in a thin slab of gas

We present general relativistic magnetohydrodynamic simulations of merging equal-mass, spinning black holes embedded in an equatorial thin slab of magnetized gas. We evolve black holes either non-spinning, with spins aligned to the orbital angular momentum, and with misaligned spins. The rest-mass density of the gas slab follows a Gaussian profile symmetric relative to the equatorial plane and it is initially either stationary or with Keplerian rotational support. As part of our diagnostics, we follow the accretion of matter onto the black hole horizons and the Poynting luminosity. Throughout the inspiral phase, the configurations with non-zero spins display modulations in the mass accretion rate that are proportional to the orbital frequency and its multiples. Our frequency analysis suggests that these modulations are influenced by the initial geometry and angular momentum of the gas distribution. In contrast to binary models evolved in the gas cloud scenario, we do not observe a significant increase in the mass accretion rate after the merger in any of our simulations. This observation brings attention to a potential link between the electromagnetic signatures of massive binary black hole mergers and the geometrical distribution of the surrounding gas. It also suggests the possibility of not detecting a peak luminosity at the time of merger in future electromagnetic observations.

astro-ph.HE↗