arXiv subjects

Filippo Camilloni

Publications and source records attributed to Filippo Camilloni.

8 recordsLinked to original sources

arXiv2026

Universality of the Blandford-Znajek emission in stationary and axisymmetric spacetimes

The Blandford-Znajek (BZ) mechanism is widely recognised as the most compelling process to extract rotational energy from an accreting black hole and power the emission of relativistic jets. We explore the universality of this process for generic black-hole spacetimes within the Konoplya-Rezzolla-Zhidenko formalism and find that the lowest-order contribution to the BZ power is invariant across different black-hole spacetimes. We also show that at the next-leading-order, different black-hole spacetimes will lead to different BZ luminosities. As a result, while slowly rotating black holes cannot be distinguished via measurements of their jet power, rapidly rotating ones have the potential of providing information on the strong-field properties of the spacetime when independent measurements of the BZ luminosity and of the black-hole angular velocity are available.

gr-qc↗

arXiv2025

Electromagnetic Energy Extraction from Kerr Black Holes: Ab-Initio Calculations

The possibility of extracting energy from a rotating black hole via the Blandford-Znajek mechanism represents a cornerstone of relativistic astrophysics. We present general-relativistic collisionless kinetic simulations of Kerr black-hole magnetospheres covering a wide range in the black-hole spin. Considering a classical split-monopole magnetic field, we can reproduce with these ab-initio calculations the force-free electrodynamics of rotating black holes and measure the power of the jet launched as a function of the spin. The Blandford-Znajek luminosity we find is in very good agreement with analytic calculations and compatible with general-relativistic magnetohydrodynamics simulations via a simple rescaling. These results provide strong evidence of the robustness of the Blandford-Znajek mechanism and accurate estimates of the electromagnetic luminosity to be expected in those scenarios involving rotating black holes across the mass scale.

gr-qc↗

arXiv2024

Self-consistent multidimensional Penrose process driven by magnetic reconnection

Astronomical observations and numerical simulations are providing increasing evidence that resistive effects in plasmas around black holes play an important role in determining the phenomenology observed from these objects. In this spirit, we present a general approach to the study of a Penrose process driven by plasmoids that are produced at reconnection sites along current sheets. Our formalism is meant to determine the physical conditions that make a plasmoid-driven Penrose process energetically viable and can be applied to scenarios that are matter- or magnetic-field-dominated, that is, in magnetohydrodynamical or force-free descriptions. By exploring reconnection from an axisymmetric but curved surface, our approach can be considered genuinely multidimensional and allows us to explore conditions that are beyond the ones explored so far and that have been restricted to the equatorial plane. Furthermore, it provides a direct contact with numerical simulations of accretion onto black holes, which exhibit an intense reconnection activity outside the equatorial plane. Finally, to describe the kinematics of the plasma self-consistently, we use the well-known configuration of an equilibrium torus with a purely toroidal magnetic field. For such a torus, we discuss the existence of an ``ergobelt'', \ie a nontrivial surface penetrating the ergosphere and acting as a natural a site for the occurrence of reconnection, and from where we estimate the energetics of a plasmoid-driven Penrose process.

gr-qc↗

arXiv2024

Binary mergers in strong gravity background of Kerr black hole

Binary-black-hole (BBH) mergers can take place close to a supermassive black hole (SMBH) while being in a bound orbit around the SMBH. In this paper, we study such bound triple systems and show that including the strong gravity effects of describing the SMBH with a Kerr metric can significantly modify the dynamics, as compared to a Newtonian point particle description of the SMBH. We extract the dynamics of the system, using a quadrupole approximation to the tidal forces due to the SMBH. We exhibit how the gyroscope precession is built into this dynamics, and find the secular Hamiltonian by both averaging over the inner and outer orbits, the latter being the orbit of the BBH around the SMBH. We study the long-time-scale dynamics, including the periastron precession and GW radiation-reaction of the binary system, finding that the strong gravity effects of the SMBH can enhance the von Zeipel-Lidov-Kozai mechanism, resulting in more cycles, higher maximum eccentricity, and thereby a shorter merger time, particularly when the binary is close to, or at, the innermost stable orbit of the SMBH. We end with an analysis of the peak frequency of the GW emission from the binary system, highlighting possible observable signatures in the LISA and ET frequency bands.

gr-qc↗

arXiv2024

Blandford-Znajek jets in MOdified Gravity

General relativity (GR) will be imminently challenged by upcoming experiments in the strong gravity regime, including those testing the energy extraction mechanisms for black holes. Motivated by this, we explore magnetospheric models and black hole jet emissions in MOdified Gravity (MOG) scenarios. Specifically, we construct new power emitting magnetospheres in a Kerr-MOG background which are found to depend non-trivially on the MOG deformation parameter. This may allow for high-precision tests of GR. In addition, a complete set of analytic solutions for vacuum magnetic field configurations around static MOG black holes are explicitly derived, and found to comprise exclusively Heun polynomials.

gr-qc↗

arXiv2023

Tidal deformations of a binary system induced by an external Kerr black hole

The dynamics of a binary system moving in the background of a black hole is affected by tidal forces. In this work, for the Kerr black hole, we derive the electric and magnetic tidal moments at quadrupole order, where the latter are computed for the first time in full generality. We make use of these moments in the scenario of a hierarchical triple system made of a Kerr black hole and an extreme-mass ratio binary system consisting of a Schwarzschild black hole and a test particle. We study how the secular dynamics of the test particle in the binary system is distorted by the presence of tidal forces from a much larger Kerr black hole. Our treatment includes strong gravitational effects beyond the post-Newtonian approximation both for the binary system and for the tidal forces since the binary system is allowed to be close to the event horizon of the Kerr black hole. We compute the shifts in the physical quantities for the secular dynamics of the test particle and show that they are gauge-invariant. In particular, we apply our formalism to the innermost stable circular orbit for the test particle and to the case of the photon sphere. Our results are relevant for the astrophysical situation in which the binary system is in the vicinity of a supermassive black hole.

gr-qc↗

arXiv2022

A stable and causal model of magnetohydrodynamics

We formulate the theory of first-order dissipative magnetohydrodynamics in an arbitrary hydrodynamic frame under the assumption of parity-invariance and discrete charge symmetry. We study the mode spectrum of Alfvén and magnetosonic waves as well as the spectrum of gapped excitations and derive constraints on the transport coefficients such that generic equilibrium states with constant magnetic fields are stable and causal under linearised perturbations. We solve these constraints for a specific equation of state and show that there exists a large family of hydrodynamic frames that renders the linear fluctuations stable and causal. This theory does not require introducing new dynamical degrees of freedom and therefore is a promising and simpler alternative to Müller-Israel-Stewart-type theories. Together with a detailed analysis of transport, entropy production and Kubo formulae, the theory presented here is well suited for studying dissipative effects in various contexts ranging from heavy-ion collisions to astrophysics.

hep-th↗

arXiv2022

Blandford--Znajek monopole expansion revisited: novel non-analytic contributions to the power emission

The Blandford and Znajek (BZ) split-monopole serves as an important theoretical example of the mechanism that can drive the electromagnetic extraction of energy from Kerr black holes. It is constructed as a perturbative low spin solution of Force Free Electrodynamics (FFE). Recently, Armas $et~al.$ put this construction on a firmer footing by clearing up issues with apparent divergent asymptotics. This was accomplished by resolving the behavior around the outer light surface, a critical surface of the FFE equations. Building on this, we revisit the BZ perturbative expansion, and extend the perturbative approach to higher orders in the spin parameter of the Kerr black hole. We employ matched-asymptotic-expansions and semi-analytic techniques to extend the split-monopole solution to the sixth-order in perturbation theory. The expansion necessarily includes novel logarithmic contributions in the spin parameter. We show that these higher order terms result in non-analytic contributions to the power and angular momentum output. In particular, we compute for the first time the perturbative contributions to the energy extraction at seventh- and eighth-order in the spin parameter. The resulting formula for the energy extraction improves the agreement with numerical simulations at finite spin. Moreover, we present a novel numerical procedure for resolving the FFE equations across the outer light surface, resulting in significantly faster convergence and greater accuracy, and extend this to higher orders as well. Finally, we include a general discussion of light surfaces as critical surfaces of the FFE equations.

gr-qc↗