arXiv subjects

Mubasher Jamil

Publications and source records attributed to Mubasher Jamil.

At least 19 recordsLinked to original sources

arXiv2026

Dark Matter Imprints on Black Hole Shadows and Chaotic Dynamics: A Comparative Study of Halo Profiles around Sgr A and M87

The gravitational influence of dark matter (DM) halos on the strong-field regime around supermassive black holes (SMBHs) remains largely unexplored. In the present work, we try to make a framework of the halo-modified space times for four well-known DM profiles including the Navarro Frenk-White (NFW), Moore, Burkert, and Dehnen-(1,4,3/4) profiles, respectively. We derive the corresponding photon spheres, shadow radii, and innermost stable circular orbits (ISCO) for the Sgr A* and M87*. We then constrain the DM halo parameters by comparing the theoretical values with the observed Event Horizon Telescope (EHT) data, and the robustness was checked by comparing the obtained virial mass of the Milky Way and M87 from the parameters with the values already present in the literature. In addition to this we extend the geodesic analysis by formulating the perturbed orbital dynamics using a Painlev\'e-Gullstrand Hamiltonian framework, and as a result we compute orbital trajectories, Poincar\'e sections, and finite-time Lyapunov ex ponents. These chaotic dynamics leave distinct imprints on gravitational waveforms, including phase irregularities and amplitude modulations.

physics.gen-ph↗

arXiv2026

Optical Signatures of Sgr A* and M87* with Dark Matter Halos

The event horizon telescope (EHT) has opened a new window onto the strong-field regime by imaging the shadows of the supermassive black holes (SMBHs) Sgr A* and M87*. These observations provide a unique laboratory for probing the dark matter (DM) distribution around black holes. In this work we systematically investigate the imprints of two distinct DM halo models, the cold DM (CDM), and the cored scalar field DM (SFDM) profiles on the gravitational lensing signatures of Sgr A* and M87*. We compute the photon spheres, shadows, weak and strong lensing observables, and caustic structures for both models. We then compared the obtained values of the shadow diameters with the EHT data, using $\chi^2$ statistics. We found that all the models are within $1.2\sigma$ of the measured shadow diameters with the small $\chi^2$ differences, $\Delta\chi^2 \lesssim 1.2$. The caustic analysis reveals distinct topological regimes, Sgr A* retains both tangential and radial critical curves, while M87* may show only tangential critical curves due to its larger mass. This topological difference provides a clear observational signature for future observations.

astro-ph.CO↗

arXiv2026

Black hole shadow parameters and quasi-normal modes for Weyl-incorporated gravity

An additional term of the form $\lambda \mathbf{T} \cdot \mathbf{C} \cdot \mathbf{T}$ in the Einstein-Hilbert Lagrangian was introduced to explain the interaction between matter and pure gravitational field [H. W. Lee and A. Qadir, Motion of test particle for Weyl-interaction gravity, {\it Int. Jour. Mod. Phys. D} {\bf 28}(16) (2019) 2040014], the modified relativistic dynamics (MORD). In this paper, we estimate the shadow parameters of black hole in a spherically symmetric static spacetime within the MORD framework. As a first approximation, we assume that the black hole is surrounded by a constant-density baryonic matter halo. The analysis is then extended by introducing a homogeneous plasma background. We compute the shadow radii for various black hole masses and analyze their dependence on the WIG coupling parameter $\lambda$. In addition, we compute the fundamental quasi-normal mode (QNM) frequencies under test-field approximation, and perform a time-domain integration analysis.

gr-qc↗

arXiv2026

Chaotic imprints of dark matter in extreme mass-ratio inspirals

Extreme mass-ratio inspirals (EMRIs) are among the most powerful probes of strong-field gravity and of the environments surrounding supermassive compact objects. Motivated by the expected presence of dark matter near galactic centers, we investigate the emergence and gravitational-wave imprints of chaotic dynamics in EMRIs evolving in non-vacuum spacetimes. Within a unified dynamical framework, we analyze test-particle motion in a broad class ofdark-matter-embedded geometries, including singular black holes, regular black holes, naked singularities, and Einstein-cluster configurations. We show that environmental perturbations generically break integrability in the strong-field regime, giving rise to chaotic motion whose onset, duration, and termination depend sensitively on horizon structure, core regularization, and matter distribution. Using the numerical Kludge approach, we demonstrate that chaotic trajectories produce systematic qualitative modifications of the emitted gravitational radiation, such as irregular amplitude modulation and loss of phase coherence, in contrast to the smooth, quasi-periodic waveforms generated by regular motion. Our results establish the robustness of chaos in environmentally perturbed EMRIs and provide a clear conceptual link between nonlinear orbital dynamics, spacetime structure, and observable gravitational-wave signatures.

gr-qc↗

arXiv2026

Shadow of F(R)-EH Black Hole and Constraints from EHT Observations

This work investigates the optical properties of a static, spherically symmetric, electrically charged black hole in f(R) gravity coupled to Euler-Heisenberg(EH) nonlinear electrodynamics(NLED). By analyzing photon trajectories in this background spacetime, we show how the model parameters affect light propagation, leading to wider ranges of lensed trajectories and photon rings. We identify regions of parameter space that admit physically consistent black hole shadows, characterized by the existence of a photon sphere located outside the event horizon and a shadow formed beyond it. These viable regions expand with increasing electric charge and increasing fR0, illustrating the interplay between gravitational and electromagnetic effects. By constraining the model using Event Horizon Telescope observations of M87*, we find that de Sitter black hole solutions remain compatible with the observational data, whereas anti-de Sitter solutions are disfavored for low electric charge and fR0 > -1. Finally, an analysis of the energy emission rate shows that higher electric charge enhances black hole evaporation, while stronger nonlinear electrodynamics effects and larger values of fR0 suppress it.

gr-qc↗

arXiv2026

Probing the nature of Einstein nonlinear Maxwell Yukawa black hole through gravitational wave forms from periodic orbits and quasiperiodic oscillations

In this work, we study gravitational wave emission from periodic orbits of test particles, analyze quasi periodic oscillations, and constrain the parameters of the static, spherically symmetric Einstein nonlinear Maxwell Yukawa black hole. Using the Hamiltonian approach, we calculate the equations of motion of the particles. We analyze the effective potential to determine the innermost stable circular orbit and innermost bound circular orbit, illustrating how the Yukawa screening parameter and electric charge Q affect orbital stability and energy requirements. Periodic orbits are classified by integer triplets and exhibit characteristic zoom whirl behavior. Based on these orbits we compute the corresponding GW signals in both the polarizations. Finally, we perform Monte Carlo Markov Chain MCMC simulations to constrain the parameters of the ENLMY BH for four microquasars and the galactic center within the relativistic precession model.

gr-qc↗

arXiv2025

Shadow geometry of Kerr MOG naked singularity and analysis of accretion disk luminosity

Naked singularities are hypothetical astrophysical entities featuring gravitational singularities without event horizons. In this study, we analyze the shadow properties of Kerr Modified Gravity (Kerr MOG) naked singularities (KMNSs). We show that the KMNS shadow can appear closed, open, or even vanish, depending on the dimensionless spin parameter a, the modified gravity parameter alpha, and the observer's inclination angle. We identify the critical conditions under which the KMNS shadow develops a gap, a unique feature not present in BH shadows. We analyze the properties of a thin accretion disk surrounding a KMNS, within the framework of MOG characterized by the parameter alpha. The study includes a detailed examination of the spacetime geometry and the equations of motion for test particles. In addition, we adopt a simplified model for the disk's radiative flux, temperature distribution, and spectral luminosity. Our analysis primarily focuses on the flux distribution of the accretion disk around KMNS with identical mass but varying spin and MOG deformation parameters. This allows us to explore how modifications in rotation and the MOG parameter alpha influence the radiative properties of the disk. Further, these observational signatures may serve as effective tools for clearly distinguishing KMNS from standard Kerr naked singularities (KNSs), where the MOG parameter alpha = 0

gr-qc↗

arXiv2025

Gravitational wave radiation from periodic orbits and quasi-periodic oscillations in Einstein non-linear Maxwell-Yukawa black hole

In this article, we investigate the orbital dynamics and quasi-periodic oscillations (QPOs) surrounding a static, spherically symmetric geometry of an Einstein-nonlinear Maxwell-Yukawa (ENMY) black hole (BH). Using the Hamiltonian formalism, we derive equations of motion and analyze the effective potential. We determine the innermost stable circular orbits (ISCO) and innermost bound circular orbits (IBCO) radii for different values of the Yukawa parameters $\lambda$ and $\delta$, and classify periodic orbits via rational frequency analysis, highlighting deviations from Schwarzschild geometry. We also study gravitational wave (GW) emission from periodic orbits and show how Yukawa terms affect GW signals. Fundamental frequencies are computed, and QPOs are analyzed using relativistic precession, warped disk, and tidal disruption models. By increasing $\lambda$, the ENLMY spacetime effectively mimics the behavior of a Schwarzschild spacetime. Constraints on the BH mass and Yukawa parameters are derived using QPO data from stellar-mass (XTE J1550-564, GRO J1655-40, GRS 1915+105), intermediate-mass (M82 X-1), and supermassive (Sgr A*) BHs within the relativistic precession model by employing a Markov Chain Monte Carlo analysis.

gr-qc↗

arXiv2025

Epicyclic oscillations and accretion disk around a special Buchdahl-inspired spacetime

In this paper, we consider the Buchdahl-inspired spacetime metric and investigate its aspects using the quasiperiodic oscillations and the accretion disk due to the accreting matter. First, we focus on analyzing the geodesics of particles around the Buchdahl-inspired spacetime, together with the conserved quantities such as specific energy and angular momentum for massive particles orbiting on the innermost stable circular orbits (ISCOs). We show that the effect of the Buchdahl parameter $\tilde{k}$ increases as the radii of the ISCO orbits decrease, resulting in shifting orbits toward the central object compared to the Schwarzschild black hole case. We also consider astrophysical epicyclic oscillations and derive their general expressions using implications of circular motion of massive particles around the Buchdahl-inspired spacetime. Further, we explore the astrophysical implications of observational higher-frequency QPOs of the selected galactic microquasars of X-ray binary systems to obtain the best-fit constraints on the Buchdahl-inspired spacetime parameters. Finally, we consider the accretion disk around the Buchdahl-inspired spacetime using implications of the ISCO parameters that define the accretion disk's inner edge. We explore radiation properties of the accretion disk and redshifted image and intensity of a lensed accretion disk around the Buchdahl-inspired spacetime.

gr-qc↗

arXiv2025

Spin precession frequencies of a test gyroscope around a naked singularity and quasi-periodic oscillations

Various studies show that the gravitational collapse of inhomogeneous matter clouds leads to naked singularity formation. We investigate here the spin precession frequency of a test gyroscope attached to a stationary observer in a rotating naked singularity spacetime. In the weak field limit, Lense-Thirring precession for rotating naked singularity and geodetic precession in the asymptotic limit for null naked singularity are found to be equal to that of a Kerr black hole and a Schwarzschild black hole, respectively. In addition, we can distinguish a rotating naked singularity and a Kerr naked singularity for an observer in the equatorial plane using spin precession. To this end, we have found the constraints on the parameters of rotating naked singularity by employing the Monte Carlo Markov Chain simulation and using the observation from five quasi-periodic sources within the relativistic precession model. Our analysis shows that the measurement of spin parameter estimate for GRO J1655-40 is in disagreement with the value found from the continuum-fitting method, while for XTEJ1859+226 and GRS 1915+105, it is inconsistent with spectral analysis results.

gr-qc↗

arXiv2025

Shadow Cast by the Kerr MOG Black Hole under the Influence of Plasma and Constraints from EHT Observations

The study of black hole (BH) shadows provide crucial insights into the nature of strong gravitational effects and the intricate structure of the spacetime surrounding BHs. In this paper, we explore the shadow of Kerr MOG BH within a plasma environment, investigating how much the presence of plasma influences the characteristics of the observed shadow compared to those in vacuum conditions. Our analysis reveals that the shadow characteristics of M87* and Sgr A* are more compatible with event horizon telescope (EHT) observational data in nonhomogeneous plasma spacetime compared to homogeneous distributions. For small metric deformation parameter $\alpha$, the shadow aligns within $2\sigma$ uncertainty for homogeneous plasma and within $1\sigma$ for nonhomogeneous plasma. Next, we determine the energy emission rate for the Kerr MOG BH and analyze the influence of parameters $\alpha$, $k_o$, $k_\theta$, and $k_r$ on particle emissions in the BH vicinity. We further analyze the deflection angle in the presence of homogeneous and nonhomogeneous plasma profiles. The findings indicate notable differences from the vacuum scenario, underscoring the importance of accounting for plasma effects in studying light propagation around compact objects.

gr-qc↗

arXiv2025

Shadows and Optical Appearances of Black Holes in $R^{2}$ Gravity

In this paper, we consider a charged AdS/dS black hole (BH) in $R^{2}$ gravity and study its optical features, including the shadow's geometrical shape and the energy emission rate. Additionally, we look for criteria to restrict the free parameters of the theory by comparing them to observational data of M87$^{\star}$. Then, we employ the Newman-Janis algorithm to build the rotating counterpart of the static solution in $R^{2}$ gravity and calculate the energy emission rate for the rotating case as well as discuss how the rotation factor and other parameters of this theory affect the emission of particles around the BHs. In the following, we consider the obtained rotating BH as a supermassive black hole and evaluate the parameters of the model with shadow size estimates based on the observations of M87$^{\star}$ from EHT.

gr-qc↗

arXiv2025

Gravitational Lensing by a Dark Compact Object in Modified Gravity and Observational Constraints from Einstein Rings

In this manuscript, we provide a comprehensive study of gravitational lensing by dark compact objects predicted by a Modified Gravity (MOG) based on the Scalar-Vector-Tensor action, and the aim is to analyze new insights into the nature of gravitational interactions. We compute weak and strong deflection angles for the specified static, spherically symmetric MOG spacetime. Additionally, we dedicate a section to explore observational implications in the weak field limit. By employing a supermassive galactic black hole as a gravitational lens, we compare various parameters in MOG with those of the Schwarzschild black hole as lens in strong-field scenarios. Specifically, we model the black holes M87${^*}$ and Sgr A${^*}$ as lenses within the MOG framework, calculating the corresponding lensing coefficients and distortion parameters in the weak field regime.

gr-qc↗

arXiv2025

Periodic orbits and their gravitational wave radiations around the Schwarzschild-MOG black hole

This article explores the motion of massive particles in the gravitational field of a modified gravity (MOG) black hole (BH), characterized by the parameter $\alpha$. Using the Hamiltonian formalism, the geodesic equations and the effective potential governing particle trajectories are derived. Key features, including the innermost stable circular orbit (ISCO) and the innermost bound circular orbit (IBCO), are analyzed, revealing their dependence on the particle's energy, angular momentum, and the MOG parameter. In the extremal case, where $\alpha=-1$, the event horizon merges with the Cauchy horizon, forming a distinctive BH configuration. Numerical methods are employed to compute periodic orbits in this spacetime, with a comparison drawn to the Schwarzschild BH. The findings indicate that for $\alpha>0$, periodic orbits around Schwarzschild-MOG BH exhibit lower energy requirements than those in Schwarzschild spacetime, whereas for $-1<\alpha<0$, the energy requirements are higher. Precessing orbits near periodic trajectories are also examined, offering insights into their complex dynamical behavior. Finally, the gravitational wave (GW) radiation from the periodic orbits of a test particle around the Schwarzschild-MOG BH is examined, generating intricate waveforms that provide insights into the gravitational structure of the system.

gr-qc↗

arXiv2025

Universal thermodynamic topological classes of black holes in perfect fluid dark matter background

In this paper, we study the universal thermodynamic topological classes of a family of black holes in a perfect fluid dark matter (PFDM) background. Recent research on black hole thermodynamics suggests that all black holes can be classified into four universal thermodynamic classes, denoted by $W^{1-}$, $W^{0+}$, $W^{0-}$, and $W^{1+}$. Our study reveals that the Schwarzschild black hole in PFDM belongs to the $W^{1-}$ class, and independence of black hole size thermodynamically unstable at both low- and high-temperature limits. The Reissner-Nordstr\"om, Kerr, and Kerr-Newman black holes in the PFDM background belong to the same universal thermodynamic class, $W^{0+}$, which represents small, stable black holes and large, unstable black holes at low-temperature limits, whereas no black hole state exists at high temperatures. The AdS black holes behave differently compared to their counterparts in PFDM. The Schwarzschild-AdS black hole belongs to the $W^{0-}$ class, indicating no black hole state at low temperatures, but small, unstable and large, stable black hole states at high temperatures. Furthermore, the Kerr-AdS black hole belongs to the $W^{1+}$ class, characterized by small, stable black holes at low temperatures, large, stable black holes at high temperatures, and unstable, intermediate-sized black holes at both low and high temperatures. These findings uncover the universal topological classifications underlying black hole thermodynamics, offering profound insights into the fundamental principles of quantum gravity.

gr-qc↗

arXiv2024

Gravitational Lensing and Image Distortion by Buchdahl Inspired Metric in $\mathcal{R}^2$ Gravity

We investigate gravitational lensing by \textit{special} Buchdahl inspired metric with the Buchdahl parameter $\tilde{k}$. In strong deflection limit, we derive the deflection angle analytically for the light rays that diverge as photons approach the photon sphere. These are then used in order to compute the angular image positions modeling supermassive black holes, Sgr A* and M87* as lenses. The Einstein rings for the outermost relativistic images are also depicted here alongside observational constraints on $\tilde{k}$ by the Einstein radius and lens mass. Constraints on $\tilde{k}$ are obtained modelling black holes ( Sgr A* and M87*) and Canarias Einstein ring. In weak deflection limit, the analytic expression of deflection angle of the subject asymptotically flat metric in $\mathcal{R}^2$ gravity is determined using the Gauss Bonnet theorem. Considering M87* as a lens, weak deflection angle is used to study the image magnification and image distortion for primary and secondary images. It is shown that image distortion satisfies the hypothesis of Virbhadra. Moreover, it is seen that our general expression of deflection angle reduces, as a special case, to the deflection angle of Schwarzschild metric in both weak and strong deflection limits.

gr-qc↗

arXiv2024

A Study of Black Holes in $F(R)-$ModMax Gravity: Gravitational Lensing and Constraints from EHT Observations

The study of astrophysical phenomena like black hole shadows is an effective approach to properly understand the modified gravity and explore its validity. Motivated by recent astrophysical observations, we consider a black hole (BH) in $F(R)-$ModMax gravity and study the optical features such as the shadow's geometrical shape, energy emission rate, and deflection of light. More specifically, we show how the variation of the model parameters imprints specific signatures on these optical quantities. In the following, we consider such black holes as supermassive BHs and evaluate the parameters of the model with shadow size estimates done by the observations of M87* from the Event Horizon Telescope (EHT). According to our findings, the parameter $f_{R_{0}}$ plays an effective role in having results consistent with the EHT data such that the resulting shadow of AdS black holes in $F(R)-$ModMax gravity agrees with the observational data for $f_{R_{0}}<-1$. However, for dS black holes, a consistent result is observed for $f_{R_{0}}>-1$.

gr-qc↗

arXiv2024

Particle Dynamics and Quasi-Periodic Oscillations in the GUP-Modified Schwarzschild Spacetime: Constraint Using Micro-Quasars Data

In this work, we have worked out dynamical aspects for the particles moving around the GUP-corrected-Schwarzschild (S-GUP) black hole. We have calculated the innermost stable circular orbit (ISCO) around black hole and explored its implications for different microquasars. Additionally, we have shown that the Kerr black hole mimics S-GUP black hole after some tuning of parameters. Finally, considering the S-GUP black hole as a microquasar source, we have studied quasi-periodic oscillation (QPO). Further utilizing the available observational data of few microquasars, we have obtained constrains on the GUP parameter $\epsilon$ as well.

gr-qc↗