arXiv subjects

G. Abbas

Publications and source records attributed to G. Abbas.

At least 19 recordsLinked to original sources

arXiv2025

Exploring the accelerating black holes from the observations of quasi-periodic oscillations in X-ray binaries

Black holes in dense astrophysical environments, such as globular clusters or in the vicinity of other massive objects, may possess accelerations. Such acceleration would modulate the characteristics of the quasi-periodic oscillations (QPOs) observed in X-ray black hole binaries. In this paper, we explore the influence of spin-aligned acceleration of a black hole on QPOs observed in X-ray binaries. For this purpose, we compute the fundamental frequencies arising from the motion of test particles around an accelerating (spin-aligned) black hole and apply the relativistic precession, parametric resonance, and forced resonance models to establish their correspondence with several observed QPOs of X-ray binaries (GRO J1655-40, XTE J1550-564, XTE J1859+226, GRS 1915+105, H1743-322, M82~X-1, and Sgr~A$^{*}$). We then employ the Bayesian Markov-Chain Monte Carlo method to constrain the black hole parameters. Our results show no evidence for spin-aligned acceleration in any of the analyzed sources, suggesting that most of these X-ray binaries reside in isolated environments and therefore experience only small perturbations to the background spacetime geometries.

astro-ph.HE↗

arXiv2025

Penrose Process Efficiency and Irreducible Mass in Rotating Einstein-Born-Infeld Black Holes with Nonlinear Electrodynamics

We investigate the extraction of rotational energy from rotating Einstein-Born-Infeld (EBI) black holes, where nonlinear electrodynamics introduces a radius-dependent effective charge modifying the spacetime geometry. Focusing on neutral test particles in the equatorial plane, we derive analytic expressions for their kinematics and establish conditions for negative energy orbits essential to the Penrose process using the near-horizon limit and Wald inequality. We present a closed-form expression for maximal energy extraction efficiency as a function of spin, charge, and the Born-Infeld parameter $\beta$. Our numerical survey reveals that increasing charge and nonlinear Born-Infeld effects generally reduce horizon radius and ergoregion size, suppressing energy extraction efficiency compared to Kerr and often Kerr-Newman black holes. However, at certain spins and \$beta$, the EBI geometry can enhance efficiency beyond Kerr-Newman. We also compute the irreducible mass, showing how nonlinear electromagnetic dynamics reduce the horizon area and the associated entropy proxy. These results provide a unified picture linking nonlinear electrodynamics, horizon structure, and energy extraction efficiency across relevant parameters.

gr-qc↗

arXiv2025

Revisiting the Penrose Process in Rotating Black Holes with Quantum Corrections: Implications for Energy Extraction and Irreducible Mass

We explore the extraction of energy from a rotating black hole spacetime modified by a quantum correction parameter $ \alpha $. Focusing on particle splitting within the ergoregion, we analyze the Penrose process and compute the extraction efficiency $ \eta $ as a function of both the spin parameter $ a $ and the quantum correction parameter $ \alpha $. Our results show that increasing $ \alpha $ induces an inward shift of the event horizon and the static limit, resulting in a modest expansion of the ergoregion. This geometric change significantly enhances the energy extraction potential. By numerically solving the horizon equation, we determine a maximum extraction efficiency of 11.64\%. Additionally, we derive the expression for the irreducible mass, highlighting its fundamental role in constraining the amount of extractable rotational energy. Overall, our findings demonstrate that quantum corrections have a substantial impact on black hole energetics, leading to marked deviations from predictions based on classical Kerr theory.

gr-qc↗

arXiv2024

Ion acoustic and spin electron acoustic cnoidal waves in a spin polarized plasma with exchange effects

Separate spin evolution-quantum hydrodynamic (SSE-QHD) model is employed to address the nonlinear propagation of ion-acoustic wave (IAW) and spin electron-acoustic wave (SEAW) in a spin polarized electron-ion plasma. The analysis has been made under the self-consistent field approximation and with exchange correlation effects. The reductive perturbation method (RPM) is used to derive KdV equation and its cnoidal wave solutions. We noted that the phase velocity of IAW in the self-consistent field approximation is almost constant however, in the presence of exchange-correlation potential there is an abrupt change in the phase velocity. The phase velocity of SEAW decreases in the presence of exchange-correlation effects as compare to self-consistent field approximation. We have calculated the condition for the existence of \ nonlinear structures and it is found that \ in the presence of exchange effect the condition satisfy for certain values of $\eta$ at different densities. Furthermore, the comparisons have been made with and without exchange effects, it shows that although the nonlinear profiles of both waves are significantly\ affected with exchange effect but it also converts cnoidal structures of SEAW from rarefactive to compressive. The influence of exchange-correlation potential and spin polarization on the \ profiles of both nonlinear structures is evaluated numerically. The present study may be helpful to understand formation of \ new longitudinal cniondal structures in laboratory degenerate plasma.

physics.plasm-ph↗

arXiv2023

Accretion disk around Reissner-Nordstr\"{o}m black hole coupled with a nonlinear electrodynamics field

The phenomenon by which matter accumulates in the vicinity of a huge celestial object is known as accretion. The gravitational energy is excreted as a consequence of infalling matter onto compact objects. The accretion procedure around celestial bodies like neutron stars, white dwarfs, and black holes has considerable importance because of its ability to transform gravitational energy into radiation. This study investigates the particle's geodesic motion and accretion around the spherically symmetric Reissner-Nordstr\"{o}m black hole coupled with a nonlinear electrodynamics field utilizing isothermal fluid. The formation of the disc-like structure in the accretion process arises from the geodesic motion exhibited by particles near the black hole. The circular orbits, radiant flux energy, radioactive efficiency, and radiant temperature, can be determined. Our study focuses on the examination of particles exhibiting stable circular orbits within the equatorial plane. We analyze the perturbations experienced by particles throughout employing restoring forces and the oscillatory behavior of the particles around a compact object. We conduct an analysis of the fluid's critical flow and maximum accretion rate. Our results show how the black hole parameter $\zeta$ and charge $q$ affect the circular geodesic of particles and the maximum accretion rate of the Reissner-Nordstr\"{o}m black hole coupled with nonlinear electrodynamics.

gr-qc↗

arXiv2023

Analysis of accretion disk around the Euler-Heisenberg Anti-de Sitter Black Hole

We demonstrate the investigation of thin accretion disc surrounding the Einstein- Euler-Heisenberg-Anti-de Sitter black hole. Additionally, we analyze the black hole event horizons and compute their effective potential and equations of motion. The specific energy, specific angular momentum, and specific angular velocity of the particles that move in circular orbits above the thin accretion disk are obtained. Also, the effects of parameters of the Einstein- Euler-Heisenberg-Anti de sitter black hole on specific angular velocity, specific heat energy, and specific angular momentum, have been discussed in detail. We display the positions of the innermost stable circular orbits and illustrate the effective potential. Furthermore, the circular orbits of black hole are obtained numerically and locates the position of the innermost stable circular orbit and event horizon. Also, we study the Gamma ray burst emitted from the Einstein Euler-Heisenberg Anti de sitter black hole.

gr-qc↗

arXiv2023

Matter accretion onto the magnetically charged Euler-Heisenberg black hole with scalar hair

This paper deals with astrophysical accretion onto the magnetically charged Euler-Heisenberg black holes with scalar hair. We examine the accretion process of a variety of perfect fluids, including polytropic and isothermal fluids of the ultra-stiff, ultra-relativistic, and sub-relativistic forms, when fluid is accreting in the vicinity of the black hole. By using the Hamiltonian dynamical approach, we can find the sonic or critical points numerically for the various types of fluids that are accreting onto the black hole. Furthermore, for several types of fluids, the solution is provided in closed form, expressing phase diagram curves. We compute the mass accretion rate of a magnetically charged Euler-Heisenberg black hole with scalar hair. We observe that the maximum accretion rate is attained for small values of the black hole parameters. We may be able to understand the physical mechanism of accretion onto black holes using the outcomes of this investigation.

gr-qc↗

arXiv2023

Thermal fluctuations, quasi-normal modes and phase transition of the charged AdS black hole with perfect fluid dark matter

In this paper, we study thermodynamics, thermal fluctuations, phase transitions and the charged anti-de Sitter black hole surrounded by perfect fluid dark matter. Large black holes are shown to be stable when subject to thermal fluctuations, and we begin by exploring how these fluctuations affect the uncorrected thermodynamic quantities of entropy, Helmholtz free energy, Gibbs free energy, enthalpy specific heat, and phase transition stability. We also discuss null geodesics and the radius of the photon sphere for the charged AdS BH and use the radius of a photon sphere to calculate the Lyapunov exponent and angular velocity. Exceptionally, we test the effects of various parameters of a black hole graphically by observing the existence of the correction parameter and the coupling parameter, which reveal the behavior of corrected thermodynamic quantities. Lastly, we see how the system is stable (under the effects of the dark matter parameter) by figuring out the specific heat and Hawking temperature, which are both related to entropy.

gr-qc↗

arXiv2023

Relativistic Polytropic Models of Charged Anisotropic Compact Object

In this paper, we have introduced new viable solutions of Einstein-Maxwell field equations by incorporating the features of anisotropic matter distribution in the realm of General theory of Relativity ($GR$). For this procurement, we have employed a Finch-Skea spacetime along with a generalized polytropic equation of state ($EoS$). We have constructed various models of generalized polytropes by assuming the different choices of the polytropic index i.e.,$\eta=\frac{1}{2}, \frac{2}{3}, 1$ and $2$. The numerous physical characteristics of these considered models have been studied via graphical analysis, which obey all the essential conditions of the astrophysical compact objects. Furthermore, such outcomes of charged anisotropic compact star models can be regained to the various cases such as linear, quadratic and polytropic $EoS$.

gr-qc↗

arXiv2023

Extended phase space thermodynamics of black hole with non-linear electrodynamic field

This paper deals with the thermodynamical properties of black hole formulated in Einstein theory of relativity and associated with a nonlinear electromagnetic field. The transition of the black hole is analyzed using the parameters mass, electric charge, coupling constant, and cosmological constant. We find-out the thermodynamical aspects of exact black hole solutions to compute the black hole mass, temperature, entropy, Gibbs free energy, specific heat and the critical exponents in the phase space. Further, we study the stability of the black hole solution by specific heat and Gibbs free energy. We look at the first and second phase changes and show a P-V criticality, which is like the Van der Waals phase change. We also examine the equation of the state and the critical exponents.

gr-qc↗

arXiv2023

Accretion disc around black hole in Einstein-$SU(N)$ non-linear sigma model

The accretion of matter onto celestial bodies like black holes and neutron stars is a natural phenomenon that releases up to $40\%$ of the matter's rest-mass energy, which is considered a source of radiation. In active galactic nuclei and X-ray binaries, huge luminosities are observed as a result of accretion. Using isothermal fluid, we examine the accretion and geodesic motion of particles in the vicinity of a spherically symmetric black hole spacetime in the Einstein-$SU(N)$ non-linear sigma model. In the accretion process, the disk-like structure is produced by the geodesic motion of particles near the black hole. We determine the innermost stable circular orbit, energy flux, radiation temperature, and radioactive efficiency numerically. In the equatorial plane, we investigate the mobility of particles with stabilities that form circular orbits. We examine perturbations of a test particle by using restoring forces and particle oscillations in the vicinity of the black hole. We analyze the maximum accretion rate and critical flow of the fluid. Our findings demonstrate how parameter $N$ influences the circular motion of a test particle as well as the maximum accretion rate of the black hole in the Einstein-$SU(N)$ non-linear sigma model.

astro-ph.HE↗

arXiv2023

Constraining study of circular orbits and accretion disk around nonlinear electrodynamics black hole

The very latest observation of $M87$ supermassive black hole (BH) by the Event Horizon Telescope (EHT) provides the accretion onto BHs is an interesting study in the theory of gravity. We study the geodesics structure and accretion near a nonlinear electrodynamics BH in strong and weak field approximations. These approximations provide the disc-like structure under the geodesic motion and accretion around the BH. Near the equatorial plane, we provide some new reasons to make circular orbits and accretion of test particles around the BH. Then we investigate perturbations, the critical speed of the fluid and the mass accretion rate of particles around the central object. The physical validity of this study shows that the parameter $\beta$ and $Q$ play an important role in the circular orbits and the mass accretion rate in strong and weak field approximations.

gr-qc↗

arXiv2020

Matter Accretion onto a Conformal Gravity Black Hole

The accretion of test fluids flowing onto a black hole is investigated. Particularly, by adopting a dynamical Hamiltonian approach, we are capable to find the critical points for various cases of black hole in conformal gravity. In these cases, we have analyzed the general solutions of accretion employing the isothermal equations of state. The steady state and spherically symmetric accretion of different test fluids onto the conformal gravity black hole has been considered. Further, we have classified these flows in the context of equations of state and the cases of conformal gravity black hole. The new behavior of polytropic fluid accretion is also discussed in all three cases of black hole. Black hole mass accretion rate is the most important part of this research in which we have investigated that the Schwarzschild black hole produce a typical signature than the conformal gravity black hole and Schwarzschild de-Sitter black hole. The critical fluid flow and the mass accretion rate have been presented graphically by the impact parameters $\beta$, $\gamma$, $k$ and these parameters have great significance. Additionally, the maximum mass rate of accretion fall near the universal and Killing horizons and minimum rate of accretion occurs in between these regions. Finally, the results are compared with the different cases of black hole available in the literature.

gr-qc↗

arXiv2020

Propagation of periodic wave trains along the magnetic field in a collision-free plasma

In this work, a systematic study, examining the propagation of periodic and solitary wave along the magnetic field in a cold collision-free plasma, is presented. Employing the quasi-neutral approximation and the conservation of momentum flux and energy flux in the frame co-traveling with the wave, the exact analytical solution of the stationary solitary pulse is found analytically in terms of particle densities, parallel and transverse velocities, as well as transverse magnetic fields. Subsequently, this solution is generalized in the form of periodic waveforms represented by cnoidal-type waves. These considerations are fully analytical in the case where the total angular momentum flux $L$, due to the ion and electron motion together with the contribution due to the Maxwell stresses, vanishes. A graphical representation of all associated fields is also provided.

nlin.PS↗

arXiv2020

Strong Gravitational Lensing for Photon Coupled to Weyl Tensor in Kiselev Black Hole

The ambition of the present work is to highlight the phenomena of strong gravitational lensing and deflection angle for the photons coupling with Weyl tensor in a Kiselev black hole. Here, we have extended the prior work of Chen and Jing \cite{1} for Schwarzschild black hole to Kiselev black hole. For this purpose, the equation of motion for the photons coupled to Weyl tensor, null geodesic and equation of photon sphere in a Kiselev black hole spacetime have been formulated. It is found that the equation of motion of the photons depends not only on the coupling between photon and Weyl tensor, but also on the polarization direction of the photons. There is a critical value of the coupling parameter $α$ for existence of the marginally circular photon orbit outside the event horizon, which depends on the parameters of black hole and the polarization direction of photons. Further, the polarization directions of coupled photon and the coupling parameter $α$, both modify the features of the photon sphere, the angle of deflection and the functions $(\bar{a}$ and $\bar{b})$ for the strong gravitational lensing in Kiselev black hole spacetime. In addition to this, the observable gravitational lensing quantities and the shadows of the Kiselev black hole spacetime are presented in detail.

gr-qc↗

arXiv2018

Models of Anisotropic Self-Gravitating Source in Einstein-Gauss-Bonnet Gravity

In this paper, we have studied gravitational collapse and expansion of non-static anisotropic fluid in $5D$ Einstein Gauss-Bonnet gravity. For this purpose, the field equations have been modeled and evaluated for the given source and geometry. The two metric functions have been expressed in terms of parametric form of third metric function. We have examined the range of parameter $β$ (appearing in the form of metric functions) for which $Θ$ the expansion scalar becomes positive/negative leads to expansion/collapse of the source. The trapped surface condition has been explored by using definition of Misner-Sharp mass and auxiliary solutions. The auxiliary solutions of the field equations involve a single function which generates two types of anisotropic solutions. Each solution can be represented in term of arbitrary function of time, this function has been chosen arbitrarily to fit the different astrophysical time profiles. The existing solutions forecast gravitational expansion and collapse depending on the choice of initial data. In this case, it has been investigated wall to wall collapse of spherical source. The dynamics of the spherical source has been observed graphically with the effects of Gauss-Bonnet coupling term $α$ in the case of collapse and expansion. The energy conditions are satisfied for the specific values of parameters in the both solutions, this implies that the solutions are physically acceptable.

gr-qc↗

arXiv2018

Complexity Factor For Anisotropic Source in Non-minimal Coupling Metric $f(R)$ Gravity

In this outline we recognize the idea of complexity factor for static anisotropic self-gravitating source with generalized $f(R)$ metric gravity theory. In present consideration, we express the Einstein field equations, hydrostatic equilibrium equation, the mass function and physical behavior of $f(R)$ model by using some observational data of well known compact stars like $4U~1820-30, SAX~J1808.4-3658$ and $Her~X-1$. We define the scalar functions through the orthogonal splitting of the Reimann-Christofell tensor and then find the vanishing complexity condition for self-gravitating system with the help of these scalars. It has been found that the vanishing condition for the complexity are pressure anisotropy and energy density inhomogeneity must cancel each other. Moreover, we study the momentous results of an astral object for the vanishing of complexity factor. Finally, these solutions reduced to previous investigation about complexity factor in General Relativity by taking $λ=0$.

gr-qc↗

arXiv2018

A New Model of Quintessence Compact Stars in Rastall Theory of Gravity

In the present work, we study a new model of anisotropic compact stars in the regime of Rastall theory. To solve the Rastall field equations we have used the Karori and Barua (KB) ansatz along with the quintessence dark energy characterized by a parameter $ω_{q}$ with $-1<ω_{q}<-\frac{1}{3}$. We present a comparative study to demonstrate the physical acceptance of our proposed model. We compare the numerical values of physical parameters obtained from our model with those of general relativity ($GR$) model given by Bhar \cite{1} and observe that our model is more compatible (for some chosen values of Rastall dimensionless parameter $γ=κλ$) with observational data than $GR$ model. For this analysis we have consider four different compact stars, $SAX J1808-3658 (SSI)$, $4U 1820-30$, $Vela X-12$ and $PSR J1416-2230$ with radii $7.07km$, $10km$, $9.99km$ and $10.3km$, respectively. In this investigation we also present some physical aspects of the proposed model necessary to check the validity of the model and inferred that our model is acceptable physically and geometrically.

physics.gen-ph↗