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Patryk Mach

Publications and source records attributed to Patryk Mach.

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.

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arXiv2025

A Monte Carlo approach to stationary kinetic disks in the Kerr spacetime

We extend a recently proposed Monte Carlo scheme for computing stationary solutions of the general-relativistic Vlasov equation to the Kerr spacetime. As an example, we focus on razor-thin configurations of a gas confined to the equatorial plane and extending to spatial infinity. We consider monoenergetic models as well as solutions corresponding to planar Maxwell-J\"{u}ttner distributions at infinity. In both cases, the components of the particle current surface density are recovered within the proposed Monte Carlo framework. Some aspects of razor-thin kinetic disk models, including an analysis of the bulk angular momentum and angular velocity, are briefly covered.

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arXiv2025

Bondi-type accretion onto a Kerr black hole in the kinetic regime

We derive an exact solution representing a Bondi-type stationary accretion of a kinetic (Vlasov) gas onto the Kerr black hole. The solution is exact in the sense that relevant physical quantities, such as the particle current density or the accretion rates, are expressed as explicit integrals, which can be evaluated numerically. We provide an analytic approximation which allows us to obtain simple formulas for the mass, energy, and angular momentum accretion rates. These formulas are used to derive characteristic time scales of the black hole mass growth and the associated spin-down in two different scenarios: assuming that the ambient energy density is either constant or decreases on a cosmological scale.

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arXiv2025

Accretion of a Vlasov gas by a Kerr black hole

We investigate the accretion of a collisionless, relativistic kinetic gas by a rotating Kerr black hole, assuming that at infinity the state of the gas is described by a distribution function depending only on the energy of the particles. Neglecting the self-gravity of the gas, we show that relevant physical observables, including the particle current density and the accretion rates associated with the mass, the energy, and the angular momentum, can be expressed in the form of closed integrals that can be evaluated numerically or approximated analytically in the slow-rotation limit. The accretion rates are computed in this manner for both monoenergetic particles and the Maxwell-J\"uttner distribution and compared with the corresponding results in the non-rotating case. We show that the angular momentum accretion rate decreases the absolute value of the black hole spin parameter. It is also found that the rotation of the black hole has a small but non-vanishing effect on the mass and the energy accretion rates, which is remarkably well described by an analytic calculation in the slow-rotation approximation to quadratic order in the rotation parameter. The effects of rotation on the morphology of the accretion flow are also analyzed.

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arXiv2025

Semiclassical causal geodesics: Minkowski spacetime case

We use an integral quantization model based on the Heisenberg-Weyl group to describe the motion of a spinless particle in the Minkowski background spacetime. This work is a sequel to a previous paper, devoted to mathematical aspects of our model: construction of the space of coherent states and properties of elementary observables. We compute transition amplitudes corresponding to a free motion of a particle between two coherent states. These amplitudes are then used to model quantum random walks of free relativistic particles. Our quantization scheme allows us to recover interference patterns occurring in a standard double-slit experiment, known from the classical approach. This result is obtained by modeling the slits in terms of eigenstates of the position operator and computing transition amplitudes between position and coherent states. We design our model in a way which allows for a future generalization to a semi-classical quantization of the geodesic motion in curved spacetimes.

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arXiv2025

Finite collisionless accretion disks in the Kerr spacetime

We construct general-relativistic kinetic models of stationary finite accretion disks in the Kerr spacetime. Our analysis generalizes a previous model of razor-thin accretion disks of collisionless gas in the Kerr spacetime, extending to infinity in the equatorial plane. We investigate monoenergetic configurations, as well as models characterized by Maxwell-J\"{u}ttner type distributions at the outer edge of the disk. In both cases, we consider particles moving along orbits reaching the outer boundary of the disk, either plunging into the black hole, or scattered by the centrifugal barrier. For Maxwell-J\"{u}ttner models, the location of the outer disk boundary affects the mass and angular momentum accretion rates at a similar order of magnitude as the temperature parameter in the assumed Maxwell-J\"{u}ttner distribution.

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arXiv2024

Integral quantization based on the Heisenberg-Weyl group

We develop a relativistic framework of integral quantization applied to the motion of spinless particles in the four-dimensional Minkowski spacetime. The proposed scheme is based on coherent states generated by the action of the Heisenberg-Weyl group and has been motivated by the Hamiltonian description of the geodesic motion in General Relativity. We believe that this formulation should also allow for a generalization to the motion of test particles in curved spacetimes. A key element in our construction is the use of suitably defined positive operator-valued measures. We show that this approach can be used to quantize the one-dimensional nonrelativistic harmonic oscillator, recovering the standard Hamiltonian as obtained by the canonical quantization. A direct application of our model, including a computation of transition amplitudes between states characterized by fixed positions and momenta, is postponed to a forthcoming article.

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arXiv2024

Kerr Geodesics in horizon-penetrating Kerr coordinates: description in terms of Weierstrass functions

We revisit the theory of timelike and null geodesics in the (extended) Kerr spacetime. This work is a sequel to a recent paper by Cie\'{s}lik, Hackmann, and Mach, who applied the so-called Biermann-Weierstrass formula to integrate Kerr geodesic equations expressed in Boyer-Lindquist coordinates. We show that a formulation based on the Biermann-Weierstrass theorem can also be applied in horizon-penetrating Kerr coordinates, resulting in solutions that are smooth across Kerr horizons. Horizon-penetrating Kerr coordinates allow for an explicit continuation of timelike and null geodesics between appropriate regions of the maximal analytic extension of the Kerr spacetime. A part of this work is devoted to a graphic visualisation of such geodesics.

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arXiv2024

Monte Carlo methods for stationary solutions of general-relativistic Vlasov systems: Planar accretion onto a moving Schwarzschild black hole

We perform Monte Carlo simulations of stationary planar accretion of a collisionless gas onto a moving Schwarzschild black hole. In this work -- a sequel to our previous paper on the Monte Carlo method for stationary general-relativistic Vlasov systems -- we demonstrate that our approach can be extended beyond the simplifying assumptions of the spherical symmetry or axial symmetry in the planar case. Our method of computing observable quantities, such as the particle current density, can be regarded as a rigorous coarse graining scheme, adapted to a numerical grid. Main difficulties are related to the appropriate parametrization of particle trajectories and a selection of parameters consistent with assumed requirements on the distribution function.

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arXiv2023

Monte Carlo methods for stationary solutions of general-relativistic Vlasov systems: Collisionless accretion onto black holes

We develop a Monte Carlo simulation method for computing stationary solutions of the general-relativistic Vlasov equation describing a gas of non-colliding particles. As specific examples, we select planar or spherically symmetric accretion models on the Schwarzschild background spacetime. In all cases the gas extends to infinity, which poses an additional difficulty in the Monte Carlo approach. We discuss models with monoenergetic particles as well as solutions obeying the Maxwell-J\"{u}ttner distribution at infinity. For all models, exact expressions for the particle current density are known or can be computed analytically. We demonstrate perfect agreement between exact expressions for the particle current density and the results of our Monte Carlo simulations.

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arXiv2023

Equatorial accretion on the Kerr black hole

We investigate stationary accretion of the collisionless Vlasov gas onto the Kerr black hole, occurring in the equatorial plane. At infinity the gas obeys the Maxwell-J\"{u}ttner distribution, restricted to the equatorial plane. In the vicinity of the black hole, the motion of the gas is governed by the spacetime geometry. We compute accretion rates of the rest-mass, the energy, and the angular momentum, as well as the particle number surface density, focusing on the dependence of these quantities on the asymptotic temperature of the gas and the black hole spin. The accretion slows down the rotation of the black hole. We present preliminary results for a Vlasov gas accretion onto a Kerr black hole moving with a velocity parallel to the equatorial plane.

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arXiv2023

Kerr Geodesics in Terms of Weierstrass Elliptic Functions

We derive novel analytical solutions describing timelike and null geodesics in the Kerr spacetime. The solutions are parameterized explicitly by constants of motion -- the energy, the angular momentum, and the Carter constant -- and initial coordinates. A single set of formulas is valid for all null and timelike geodesics, irrespectively of their radial and polar type. This uniformity has been achieved by applying a little-known result due to Biermann and Weierstrass, regarding solutions of a certain class of ordinary differential equations. Different from other expressions in terms of Weierstrass functions, our solution is explicitly real for all types of geodesics. In particular, for the first time the so-called transit orbits are now expressed by explicitly real Weierstrass functions.

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arXiv2022

Accretion of the relativistic Vlasov gas in the equatorial plane of the Kerr black hole

We investigate stationary accretion of the collisionless Vlasov gas onto the Kerr black hole, occurring in the equatorial plane. The solution is specified by imposing asymptotic boundary conditions: at infinity the gas obeys the Maxwell-J\"{u}ttner distribution, restricted to the equatorial plane (both in positions and momenta). In the vicinity of the black hole, the motion of the gas is governed by the spacetime geometry. We compute accretion rates of the rest-mass, the energy, and the angular momentum, as well as the particle number surface density, focusing on the dependence of these quantities on the asymptotic temperature of the gas and the black hole spin. The rest-mass and energy accretion rates, normalized by the black hole mass and appropriate asymptotic surface densities of the gas, increase with increasing asymptotic temperature. The accretion slows down the rotation of the black hole.

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arXiv2022

Revisiting timelike and null geodesics in the Schwarzschild spacetime: general expressions in terms of Weierstrass elliptic functions

The theory of Schwarzschild geodesics is revisited. Basing on a result by Weierstrass and Biermann, we derive a formula describing all non radial, timelike and null trajectories in terms of Weierstrass elliptic functions. Quite remarkably, a single formula works for an entire geodesic trajectory, even if it passes through turning points. Using this formula, we derive expressions for the proper and coordinate time along the geodesic.

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arXiv2022

Accretion of the relativistic Vlasov gas onto a moving Schwarzschild black hole: Low-temperature limit and numerical aspects

New developments related to our recent study of the accretion of the Vlasov gas onto a moving Schwarzschild black hole are presented. We discuss the low-temperature limit of the mas accretion rate and a simple Monte Carlo simulation used to check the results obtained in this limit. We also comment on several numerical aspects related with momentum integrals expressing the particle density current and the particle density.

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arXiv2022

Steady critical accretion onto black holes: selfgravity and sonic point characteristics

The spherically symmetric steady accretion of polytropic perfect fluids onto a black hole is the simplest flow model that can demonstrate effects of backreaction (selfgravity). It has been discovered 16 years ago that backreaction does not influence some ("intensive") characteristics of sonic points, under suitable conditions. Herein we consider a wider class of equations of state, with polytropic indices in the range (1,2], and establish detailed boundary conditions that allow one to prove this fact. We find also numerical examples showing limits of our analytic criteria - if suitable analytic conditions are not satisfied, then selfgravity influences all characteristics of sonic points. That fact constrains the applicability of the recent proposal of Baumgarte and Shapiro to estimate the lifetime of black holes within compact stellar objects.

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arXiv2021

Toroidal magnetic fields in self-gravitating disks around black holes

We investigate stationary models of magnetized, self-gravitating disks around black holes. The disks are assumed to rotate according to a recently introduced Keplerian rotation law. We consider different prescriptions of the toroidal magnetic field. Similarly to the purely hydrodynamical case (i.e., with no magnetic field), we observe a bifurcation in the parameter space of solutions. There are usually two branches of solutions: a branch corresponding to relatively light disks and a branch for which the disk can be more massive than the black hole. The existence of this latter branch can be explained by geometric properties of the spacetime. We investigate the influence of the magnetic field in the disk on these effects.

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