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Łukasz Bratek

Publications and source records attributed to Łukasz Bratek.

At least 19 recordsLinked to original sources
arXiv2025

Phenomenological Scaling Relations for SQM Stars with a Massive s-Quark in Gravitationally Strong Magnetic Fields under the Spherical Symmetry Approximation

Scaling relations with the bag constant parameter are investigated for Strange Quark Matter (SQM) stars in the presence of gravitationally strong magnetic fields minimally coupled with matter, considering both massless and massive strange quark scenarios. Assuming a simple model for such coupling under the approximation of spherical symmetry, a phenomenological scaling formula for the maximum mass of stars is derived as a function of the surface magnetic field and the strange quark mass. This formula is applicable for all formally admissible values of the free parameters, and strict scaling with the bag constant is retained only for a vanishing strange quark mass. As a byproduct of this study, the mathematical structure of the equation of state for the relativistic SQM model with a massive strange quark is revisited without approximations. It is observed that the contribution of the electron term to the energy density cannot be neglected in the theoretical limit of large strange quark masses. Consequently, the maximum mass of SQM stars increases with sufficiently large strange quark mass, contrasting with the behavior observed for low strange quark masses.

astro-ph.HE↗
arXiv2025

Magnetic Monopoles: Theoretical Insights into the Cosmic Ray Conundrum

Ultra-high energy (UHE) photons above 10^{18} eV serve as valuable probes of fundamental physics. While typically produced in interactions involving charged particles, they could also originate from exotic sources such as annihilations of magnetically charged monopole-antimonopole pairs or decays of highly accelerated monopoles (10^{21} eV). Detecting such photons would impose constraints on monopole properties. Despite strong theoretical motivations and extensive experimental searches, no monopoles have been observed to date. A possible explanation beyond high monopole masses arises from Staruszkiewicz's quantum theory of infrared electromagnetic fields. His argument, rooted in the positivity of the Hilbert space norm, suggests that isolated magnetic monopoles may not be physically realizable. If correct, this would imply that while monopoles remain mathematically well-defined within field theories, only magnetically neutral configurations could exist in nature.

hep-ph↗
arXiv2025

Oscillations of hypothetical strange stars as an efficient source ultra-high-energy particles

We investigate the dynamical behavior of strange quark matter (SQM) objects, such as stars and planets, when subjected to radial oscillations induced by tidal interactions in stellar systems. Our study demonstrates that SQM objects can efficiently convert mechanical energy into hadronic energy due to the critical mass density at their surfaces of 4.7*10^{14} g/cm^3, below which SQM becomes unstable and decays into photons, hadrons, and leptons. We show that even small-amplitude radial oscillations, with a radius change of as little as 0.1%, can result in significant excitation energies near the surface of SQM stars. This excitation energy is rapidly converted into electromagnetic energy over short timescales approximately 1 ms, potentially leading to observable astrophysical phenomena. Higher amplitude oscillations may cause fragmentation or dissolution of SQM stars, which has important implications for the evolution of binary systems containing SQM objects and the emission of gravitational waves.

astro-ph.HE↗
arXiv2022

Cylindrically symmetric radial accretion onto a Levi-Civita string-like source

Radial steady-state accretion of polytropic matter is investigated under cylindrical symmetry in the Levi-Civita background metric. The model can be considered as a cylindrical analog of Bondi accretion in strong gravitational field. As a byproduct of this study, the issue of defining the line mass density is addressed and the role of the metric free parameters is discussed on the example of physical observables. The form of radial accretion equations is insensitive to the structure of the interior solution. Accordingly, the accretion solution analysis can be limited to a special Wilson form of Levi-Civita metric describing a structureless homogeneous string.

gr-qc↗
arXiv2022

On the issue of magnetic monopoles in the prospect of UHE photon searches

(also inside: this manuscript introduces the reader to the argument against the existence of magnetic monopoles, which forms an essential part of Staruszkiewicz's Quantum Mechanics of the Electric Charge) Ultra-high energy (UHE) photons with energies exceeding $10^{18}\eV$ can potentially be observed. They are produced in various processes involving electrically charged particles. However, more exotic scenarios are also possible. UHE photons could be emitted in encounters of massive magnetically charged monopole--antimonopole pairs or in processes associated with monopoles accelerated to high energies, typically $10^{21}\eV$ or beyond. Observing UHE photons can pose constraints on the properties of magnetic monopoles. There are compelling theoretical reasons in favor of the presence of magnetic monopoles in nature. The predicted observational signatures of these particles are therefore searched for in dedicated experiments currently in operation. Despite these attempts, magnetic monopoles have yet to be empirically proved. There are also theoretical reasons why magnetic monopoles allowed by Dirac's theory might not be realized in nature in the form of isolated particles. Detection or non-detection of UHE photon signatures of magnetic monopoles would bring us closer to solving this fascinating puzzle.

hep-th↗
arXiv2020

Oscillating Strange Quark Matter Objects Excited in Stellar Systems

It is shown that strange quark matter (SQM) objects, stars, and planets, can very efficiently convert the mechanical energy into hadronic energy when they oscillate. This is because the mass density at the edge of SQM objects, $ρ_0{=}4.7{\times}10^{14}\frac{\mathrm{g}}{\mathrm{cm}^3}$, is the critical density below which SQM is unstable with respect to decay into photons, hadrons, and leptons. We consider here radial oscillations of SQM objects that could be induced in stellar or planetary systems where tidal interactions are ubiquitous. Oscillations of $0.1\%$ radius amplitude already result in $1\,$keV per unit baryon number excitation near the surface of SQM stars. The excitation energy is converted into electromagnetic energy in a short time of 1 ms, during a few oscillations. Higher amplitude oscillations result in faster energy release that could lead to fragmentation or dissolution of SQM stars. This would have significant consequences for hypothetical SQM star binaries and planetary systems of SQM planets with regard to gravitational wave emission.

astro-ph.HE↗
arXiv2019

Nakedly singular counterpart of Schwarzschild's incompressible star. A barotropic continuity condition in the center

A static sphere of incompressible fluid with uniform proper energy density is considered as an example of exact star-like solution with weakened central regularity conditions characteristic of a nakedly singular spherical vaccuum solution. The solution is a singular counterpart of the Schwarzschild's interior solution. The initial condition in the center for general barotropic equations of state is established.

gr-qc↗
arXiv2019

Cylindrically Symmetric Spiraling Accretion in Power-law and Logarithmic Potentials

We study cylindrically symmetric steady-state accretion of polytropic test matter spiraling onto the symmetry axis in power-law and logarithmic potentials. The model allows one to qualitatively understand the accretion process in a symmetry different from that of the classical Bondi accretion. We study the integral curves as level lines of some Hamiltonian and also apply this method to Bondi accretion. The isothermal solutions in power-law potentials (as well as in any radius-dependent potential) can be expressed in exact form in terms of the Lambert W function, while in the case of logarithmic potential, exact solutions can be found for any polytropic exponent.

astro-ph.HE↗
arXiv2018

Detection of Cosmic-Ray Ensembles with CREDO

One of the main objectives of cosmic-ray studies are precise measurements of energy and chemical composition of particles with extreme energies. Large and sophisticated detectors are used to find events seen as showers starting in the Earth's atmosphere with recorded energies larger than 100 EeV. However, a Cosmic-Ray Ensemble (CRE) developing before reaching the Earth as a bunch of correlated particles may spread over larger areas and requires an extended set of detectors to be discovered. The Cosmic-Ray Extremely Distributed Observatory (CREDO) is a solution to find such phenomena. Even simple detectors measuring the particle arrival time only are useful in this approach, as they are sufficient both to provide candidate CRE events and to determine the direction from which they are arriving.

astro-ph.IM↗
arXiv2016

Magnetic flux density from the relative circular motion of stars and partially ionized gas in the Galaxy mid-plane vicinity

Observations suggest a slower stellar rotation relative to gas rotation in the outer part of the Milky Way Galaxy. This difference could be attributed to an interaction with the interstellar magnetic field. In a simple model, fields of order 10 micro Gauss are then required, consistently with the observed values. This coincidence suggests a tool for estimating magnetic fields in spiral galaxies. A North-South asymmetry in the rotation of gas in the Galaxy could be of magnetic origin too.

astro-ph.GA↗
arXiv2016

Relativistic Ideal Clock

Two particularly simple ideal clocks exhibiting intrinsic circular motion with the speed of light and opposite spin alignment are described. The clocks are singled out by singularities of an inverse Legendre transformation for relativistic rotators of which mass and spin are fixed parameters. Such clocks work always the same way, no matter how they move. When subject to high accelerations or falling in strong gravitational fields of black holes, the clocks could be used to test the clock hypothesis.

math-ph↗
arXiv2015

Velocity dispersion as a factor modifying the distribution of mass in disk-like galaxies -- an example of galaxy UGC 6446

Within the disk model framework used to approximately describe flattened galaxies, we develop an iterative method of determining column mass density from rotation curve supplemented with isotropic velocity dispersion profile. This generalizes our previous iterative method to the case when the velocity dispersion becomes important. We show on the example of UGC 6446 galaxy, that taking the velocity dispersion into account results in some observational signatures in the behavior of the local mass-to-light ratio. Along with galactic magnetic fields, this is another factor allowing to substantially reduce the local mass-to-light ratio at galactic outskirts. Taking the velocity dispersion into account may also have some consequences for the division of mass distribution between various mass components in modeling rotation curves.

astro-ph.GA↗
arXiv2015

Modeling vertical structure in circular velocity of spiral galaxy NGC 4244

We study the vertical gradient in azimuthal velocity of spiral galaxy NGC 4244 in a thin disk model. With surface density accounting for the rotation curve, we model the gradient properties in the approximation of quasi-circular orbits and find the predictions to be consistent with the gradient properties inferred from measurements. This consistency may suggest that the mass distribution in this galaxy is flattened.

astro-ph.GA↗
arXiv2015

Velocity-density twin transforms in thin disk model

Ring mass density and the corresponding circular velocity in thin disk model are known to be integral transforms of one another. But it may be less familiar that the transforms can be reduced to one-fold integrals with identical weight functions. It may be of practical value that the integral for the surface density does not involve the velocity derivative, unlike the equivalent and widely known Toomre's formula.

astro-ph.GA↗
arXiv2015

Motion of halo compact objects in the gravitational potential of a low-mass model of the Galaxy

Recently, we determined a lower bound for the Milky Way mass in a point mass approximation. This result was obtained for most general spherically symmetric phase-space distribution functions consistent with a measured radial velocity dispersion. As a stability test of these predictions against a perturbation of the point mass potential, in this paper we make use of a representative of these functions to set the initial conditions for a simulation in a more realistic potential of similar mass and accounting for other observations. The predicted radial velocity dispersion profile evolves to forms still consistent with the measured profile, proving structural stability of the point mass approximation and the reliability of the resulting mass estimate of $2.1\times10^{11}\mathrm{M}_{\odot}$ within $150\,\mathrm{kpc}$. We also find an interesting coincidence with the recent estimates based on the kinematics of the extended Orphan Stream. As a byproduct, we obtain the equations of motion in axial symmetry from a nonstandard Hamiltonian, and derive a formula in the spherical symmetry relating the radial velocity dispersion profile to a directly measured kinematical observable.

astro-ph.GA↗
arXiv2014

Constraining the vertical structure of the Milky Way rotation by microlensing in a finite-width global disk model

In this paper we model the vertical structure of mass distribution of the Milky Way galaxy in the framework of a finite-width global disk model. Assuming the Galactic rotation curve only, we test inside the solar orbit the predictions of the model for two measurable and unrelated to each other processes: the gravitational microlensing that allows to fix the disk width-scale by the best fit to measurements, and the vertical gradient of rotation modelled in the quasi-circular orbits approximation. The former is sensitive to the gravitating mass in compact objects and the latter is sensitive to all kinds of gravitating matter. The analysis points to a small width-scale of the considered disks and, at most, insignificant contribution of non-baryonic dark mater in the solar circle. The predicted high vertical gradient values in the rotation are consistent with the gradient measurements.

astro-ph.GA↗
arXiv2014

A lower bound on the Milky Way mass from general phase-space distribution function models

We model the phase-space of the kinematic tracers using general, smooth distribution functions to derive a conservative lower bound on the total mass within 150-200 kpc. By approximating the potential as Keplerian, the phase-space distribution can be simplified to that of a smooth distribution of energies and eccentricities. Our approach naturally allows for calculating moments of the distribution function, such as the radial profile of the orbital anisotropy. We construct a family of phase-spaces with the resulting radial velocity dispersion overlapping with that of distant kinematic tracers, while making no assumptions about the density of the tracers and the radial profile of the velocity anisotropy (beta). While there is no apparent upper bound for the Milky Way mass, at least as long as only the radial motions are concerned, we find a sharp lower bound for the mass that is small. In particular, a mass value of $2.4 \times 10^{11}$ of solar masses, is still consistent with the dispersion profile at larger radii. Compared with much greater mass values in the literature, this result shows that determining the Milky Way mass is strongly model dependent. We expect a similar reduction of mass estimates in models assuming more realistic mass profiles.

astro-ph.GA↗