arXiv subjects

Audrey Trova

Publications and source records attributed to Audrey Trova.

At least 19 recordsLinked to original sources

arXiv2026

Relativistic figures of equilibrium in the Wald magnetosphere

We consider a self-gravitating, rigidly rotating charged perfect fluid immersed in the Wald magnetosphere, constructed out of two linearly independent Killing vectors present in stationary and axially-symmetric spacetimes. We show that in non-vacuum spacetimes, Wald's solution can be compatible with the electric current associated with a rotating charged perfect fluid characterized by the vanishing electric conductivity. We prove that for rigidly rotating fluids with a constant energy density or described by the polytropic equation of state, the resulting equations expressing the conservation of the energy-momentum tensor can be integrated. Consequently, the system can be described by nearly standard Einstein-Euler equations known from the theory of general-relativistic rotating fluids, with modifications introduced in the Euler-Bernoulli equation. Numerical solutions of the Einstein-Euler equations are provided for these two cases by introducing suitable modifications in the pseudospectral code by Ansorg, Kleinw\"{a}chter, and Meinel.

gr-qc↗

arXiv2026

Twisted doughnuts: Thick disk torus around equatorial asymmetric black hole

The Kerr black hole spacetime is symmetric with respect to a well-defined equatorial plane. When such a symmetry is broken, for instance, by some putative effects beyond general relativity, the Keplerian circular orbits around the black hole are distorted vertically away from the equatorial plane by an amount depending on the orbital radius. As a result, the Keplerian thin disk acquires a curved surface. In this work, we extend such results to thick tori configurations by considering non-self-gravitating Polish doughnut models. We show that due to the equatorial asymmetry of the spacetime, the centers and the cusps of tori are distorted away from the original equatorial plane toward the same direction as that experienced by the stable Keplerian orbits, and the entire tori configurations are twisted toward that direction as well. The shape of the distorted tori is demonstrated explicitly using a constant specific angular momentum profile $\ell(r,y)=\ell_0$ of the disk fluid. However, the result also applies to non-constant profiles of $\ell(r,y)$ generically in the sense that any asymmetric profile of $\ell(r,y)$ that attempts to produce a symmetric tori configuration either turns out to be ill-defined near the equatorial plane or suffers from fine-tuning issues.

gr-qc↗

arXiv2025

Non-Keplerian Charged Accretion Disk Orbiting a Black Hole~Pulsar

Recent studies have focused on how spinning black holes (BHs) within a binary system containing a strongly magnetized neutron star, then immersed in external magnetic fields, can acquire charge through mechanisms like the Wald process and how this charge could power pulsar-like electromagnetic radiation. Those objects called ``Black hole pulsar'' mimic the behaviour of a traditional pulsar, and they can generate electromagnetic fields, such as magnetic dipoles. Charged particles within an accretion disk around the black hole would then be influenced not only by the gravitational forces but also by electromagnetic forces, leading to different geometries and dynamics. In this context, we focus here on the interplay of the magnetic dipole and the accretion disk. We construct the equilibrium structures of non-conducting charged perfect fluids orbiting Kerr black holes under the influence of a dipole magnetic field aligned with the rotation axis of the BH. The dynamics of the accretion disk in such a system are shaped by a complex interplay between the non-uniform, non-Keplerian angular momentum distribution, the black hole's induced magnetic dipole, and the fluid's charge. We show how these factors jointly influence key properties of the disk, such as its geometry, aspect ratio, size, and rest mass density.

astro-ph.HE↗

arXiv2024

Equilibrium of charged fluid around a Kerr black hole immersed in a magnetic field: variation of angular momentum

The present work presents analytically constructed equilibrium structures of charged perfect fluids orbiting Kerr Black holes embedded in an asymptotically uniform magnetic field. Our focus is on the effect of the non-constant angular momentum distribution through the disk, as well as its combined effect with the external magnetic field and the fluid charge. We demonstrate that the three parameters of our study have a significant impact on the various features of the accretion disk: the shape, the size of the disk and the characteristic of the fluid, as the pressure and the rest-mass density. Through our investigation, we observe substantial deviations from both the uncharged thick disk model and the charged disk model with constant angular momentum.

gr-qc↗

arXiv2024

Stability of Rotating, Charged Fluids: Generalization of the Hoiland Conditions in Newtonian Non-conductive Case

We study the conditions for stability of electrically charged, non-conductive perfect fluid tori with respect to linear perturbations. To this end we employ Lagrangian perturbation formalism and we assume a system where the fluid orbits a central body. Gravitational field of the latter is described in the Newtonian framework. We first formulate the criteria valid for a general, non-axisymmetric situation, and then we concentrate on the axisymmetric model in more detail. In the latter case we generalize the H{\o}iland criterion of stability to non-vanishing electric charge and classify special examples. Toroidal structures with constant angular momentum distribution are found to be linearly stable. Subsequently, like in the uncharged case, rotating charged fluids are found to be unstable with respect to non-axisymmetric perturbations.

gr-qc↗

arXiv2022

Oscillation properties of relativistic tori in the vicinity of a distorted deformed compact object

This paper studies the oscillation properties of relativistic, non-self-gravitating tori in the background of a distorted deformed compact object. This work concentrates on the static and axially symmetric metric containing two quadrupole parameters; relating to the central object and the external fields. This metric may associate the observable effects to these parameters as dynamical degrees of freedom. The astrophysical motivation for choosing such a field is the possibility of constituting a reasonable model for an actual scenario occurring in the vicinity of compact objects. This paper aims to investigate the radial epicyclic frequency in a perfect fluid disk and not a test particle scenario via a local analysis. To achieve this goal, we employ the vertically integrated technique to able to treat the equation analytically. The tori are also modelled with Keplerian and non-Keplerian distributions of specific angular momentum, and we discuss the dependence of oscillation properties on the variable of the model related to angular momentum distribution and quadrupoles. In the present contribution, we further explore these properties with the possibility of relating oscillatory frequencies to some high-frequency quasi-periodic oscillations models and observed data.

gr-qc↗

arXiv2022

Relativistic equilibrium fluid configurations around rotating deformed compact objects

We investigate the physical properties of equilibrium sequences of non-self-gravitating surfaces that characterize thick disks around a rotating deformed compact object described by a stationary generalization of the static q-metric. The spacetime corresponds to an exact solution of Einstein's field equations so that we can perform the analysis for arbitrary values of the quadrupole moment and rotation parameter. To study the properties of this disk's model, we analyze bounded trajectories in this spacetime. Further, we find that depending on the values of the parameters, we can have various disc structures that can easily be distinguished from the static case and also from the Schwarzschild background. We argue that this study may be used to evaluate the rotation and quadrupole parameters of the central compact object.

gr-qc↗

arXiv2022

Magnetized tori around a uniformly accelerating black hole

We generalise the relativistic accretion thick disc model to the background of a spinning charged accelerating black hole described by the C-metric to study the effects of this background on the disc model. We show the properties of this accretion disc model and its dependence on the initial parameters. This background can be distinguishable from the Kerr space-time by analysing the observing features of accretion discs.

astro-ph.HE↗

arXiv2021

Magnetised relativistic accretion disc around a spinning, electrically charged, accelerating black hole: case of C-metric

This paper examines the general relativistic model of a geometrically thick configuration of an accretion disc around an electrically charged black hole in an accelerated motion, as described by the C-metric family. We aim to study the effects of the spacetime background on the magnetised version of the thick disc model via the sequences of figures of equilibrium. While maintaining the assumption of non-selfgravitating (test) fluid, we newly explore the influence of the strength of the large-scale magnetic field with field lines organised over the length-scale of the black hole horizon. We systematically analyze the dependence on a very broad parameter space of the adopted scenario. We demonstrate that the C-metric can, in principle, be distinguished from Kerr black hole metric by resolving specific (albeit rather fine) features of the torus, such as the location of its centre, inner and outer rims, and the overall shape. The analytical setup can serve as a testbed for numerical simulations.

astro-ph.HE↗

arXiv2021

Dynamics of charged particles and quasi-periodic oscillations in the vicinity of a distorted, deformed compact object embedded in a uniform magnetic field

This work presents the dynamic properties of charged test particles influenced by the gravitational and electromagnetic fields. Accordingly, in this work, we concentrate on the static and axially symmetric metric containing two quadrupole parameters. One relates to the central object, and another relates to the external distribution of matter. This metric may associate the observable effects to these parameters as dynamical degrees of freedom. The astrophysical motivation for choosing such a field is the possibility to constitute a reasonable model for an actual situation occurring in the objects' vicinity. To test the role of large-scale magnetic fields in accretion processes, we start by analyzing different bound orbits of timelike orbits under the influence of the system's different parameters. This leads to examining their stability concerning radial and/or vertical oscillations. The main focus is to discuss the effect of magnetic field on the oscillation modes' resonant phenomena using different resonant models for disc-oscillation modes. In the present contribution, we further explore the possibility of relating oscillatory frequencies of charged particles to the frequencies of the high-frequency quasi-periodic oscillations observed in the microquasars GRS 1915+105, XTE 1550-564 and GRO 1655-40 via assuming the relevance of resonant phenomena of the radial and vertical oscillations.

astro-ph.HE↗

arXiv2021

Quasi-periodic oscillatory motion of particles orbiting a distorted deformed compact object

This work explores the dynamic properties of test particles surrounding a distorted, deformed compact object. The astrophysical motivation was to choose such background, which could constitute a more reasonable model of a real situation that arises in the vicinity of compact objects with the possibility of having parameters as the extra physical degrees of freedom. This can facilitate associating observational data with astrophysical systems. This work's main goal is to study the dynamic regime of motion and quasi-periodic oscillation in this background, depending on different parameters of the system. Also, we exercise the resonant phenomena of the radial and vertical oscillations at their observed quasi-periodic oscillations frequency ratio of 3:2.

astro-ph.HE↗

arXiv2020

Magnetized tori in the background of a deformed compact object

This paper studied the relativistic accretion thick disc model raised by a deformed compact object that slightly deviated from spherical up to the quadrupole moment by utilising $\rm q$-metric. This metric is the simplest asymptotically flat solution of Einstein's equation with quadrupole moment. This work aims to study the effects of quadrupole moments in combination with the parameters of the thick magnetised disc model via studying the properties of these equilibrium sequences of magnetised, non-self-gravitating discs in this space-time. We employed different angular momentum distributions and discussed the procedure of building this toroidal disc model based on a combination of approaches previously considered in the literature. We have shown the properties of this relativistic accretion disc model and its dependence on the initial parameters. Besides, this theoretical model can be served as the initial data for numerical simulations.

astro-ph.HE↗

arXiv2020

Effect of an external mass distribution on the magnetized accretion disk

In this paper, we constructed the magnetized thick disk model analytically around the static black hole in the presence of an external distribution of matter up to the quadrupole moment. This space-time is a solution to Einstein's field equation describing the exterior of a static and axially symmetric object locally. This work aims to study this space-time and the effects of quadrupole moments via studying the properties of the equilibrium sequences of magnetized, non-self-gravitating disks in this space-time. We discussed a procedure to build the thick disk model based on a combination of two approaches previously considered in the literature. We have examined different angular momentum distributions, and We have shown the properties of this relativistic accretion disc model in this background.

astro-ph.HE↗

arXiv2019

Relativistic and Newtonian fluid tori with electric charge

We discuss the effects of electric charging on the equilibrium configurations of magnetized, rotating fluid tori around black holes of different mass. In the context of gaseous/dusty tori in galactic nuclei, the central black hole dominates the gravitational field and it remains electrically neutral, while the surrounding material acquires some electric charge and exhibits non-negligible self-gravitational effect on the torus structure. The structure of the torus is influenced by the balance between the gravitational and electromagnetic forces. A cusp may develop even in Newtonian tori due to the charge distribution.

astro-ph.HE↗

arXiv2018

Charged fluid structures around a rotating compact object with a magnetic dipole field

We study stationary, electrically charged fluid structures encircling a rotating compact object with a dipole magnetic field oriented along the rotation axis. This situation is described in an idealized way by the Kerr metric and a magnetic dipole "test" field, that does not affect the spacetime. The self-gravitational and self-electromagnetic field of the fluid are neglected and the fluid is assumed to be non conductive and in rigid motion. Our work generalizes a previous study by Kovář et al.(2016) by taking into account the rotation of the central object. Therefore, we focus on the influence of the rotation onto the existence and position of bound fluid structures. Frame dragging effects allow the existence of polar clouds, which could not be found in non-rotating case. Furthermore counter-rotating equatorial tori become more preferred the faster the central object is spinning.

astro-ph.HE↗

arXiv2014

A truly Newtonian softening length for disc simulations

The softened point mass model is commonly used in simulations of gaseous discs including self-gravity while the value of associated length λremains, to some degree, controversial. This ``parameter'' is however fully constrained when, in a discretized disc, all fluid cells are demanded to obey Newton's law. We examine the topology of solutions in this context, focusing on cylindrical cells more or less vertically elongated. We find that not only the nominal length depends critically on the cell's shape (curvature, radial extension, height), but it is either a real or an imaginary number. Setting λas a fraction of the local disc thickness -- as usually done -- is indeed not the optimal choice. We then propose a novel prescription valid irrespective of the disc properties and grid spacings. The benefit, which amounts to 2-3 more digits typically, is illustrated in a few concrete cases. A detailed mathematical analysis is in progress.

astro-ph.IM↗

arXiv2014

Electrically charged matter in rigid rotation around magnetized black hole

We study charged-fluid toroidal structures surrounding a non-rotating charged black hole immersed in a large-scale, asymptotically uniform magnetic field. In continuation of our former study on electrically charged matter in approximation of zero conductivity, we demonstrate existence of orbiting structures in permanent rigid rotation in the equatorial plane, and charged clouds hovering near the symmetry axis. We constrain the range of parameters that allow stable configurations and derive the geometrical shape of equi-pressure surfaces. Our simplified analytical study suggests that these regions of stability may be relevant for trapping electrically charged particles and dust grains in some areas of the black hole magnetosphere, being thus important in some astrophysical situations.

gr-qc↗

arXiv2014

Self-gravity in curved mesh elements

The local character of self-gravity along with the number of spatial dimensions are critical issues when computing the potential and forces inside massive systems like stars and disks. This appears from the discretisation scale where each cell of the numerical grid is a self-interacting body in itself. There is apparently no closed-form expression yet giving the potential of a three-dimensional homogeneous cylindrical or spherical cell, in contrast with the Cartesian case. By using Green's theorem, we show that the potential integral for such polar-type 3D sectors -- initially, a volume integral with singular kernel -- can be converted into a regular line-integral running over the lateral contour, thereby generalising a formula already known under axial symmetry. It therefore is a step towards the obtention of another potential/density pair. The new kernel is a finite function of the cell's shape (with the simplest form in cylindrical geometry), and mixes incomplete elliptic integrals, inverse trigonometric and hyperbolic functions. The contour integral is easy to compute; it is valid in the whole physical space, exterior and interior to the sector itself and works in fact for a wide variety of shapes of astrophysical interest (e.g. sectors of tori or flared discs). This result is suited to easily providing reference solutions, and to reconstructing potential and forces in inhomogeneous systems by superposition. The contour integrals for the 3 components of the acceleration vector are explicitely given.

astro-ph.IM↗