arXiv subjects

Manahil Ali

Publications and source records attributed to Manahil Ali.

4 recordsLinked to original sources

arXiv2026

Optical Appearance of a Rotating Black Hole in Nonlinear Electrodynamics Surrounded by Thin Accretion Disks

This work investigates the optical appearance of a rotating black hole (BH) in nonlinear electrodynamics (NED) using two illumination models, namely a celestial sphere and a thin accretion disk. The BH images are constructed using a backward ray-tracing method together with a fisheye camera model. We examine the effects of the electric charge $Q$ and the NED parameter $\beta$ on the event horizon, shadow, photon ring, and optical appearance for both prograde and retrograde accretion flows. The results indicate that an increase in $\beta$ leads to a larger shadow radius with reduced distortion, whereas increasing $Q$ decreases the shadow size and enhances its deformation. These features are further quantified through the shadow radius and distortion parameter. We also analyze the direct and lensed images of the thin accretion disk, together with their corresponding redshift distributions and emission bands. The redshifted emission is found to dominate the observed images, while the blueshifted region is confined to the vicinity of the photon ring. Our results demonstrate that both $Q$ and $\beta$ leave distinct signatures on the optical appearance of rotating NED BHs, providing useful insights for future high-resolution observations.

gr-qc↗

arXiv2026

Probing Primordial Cosmology Through BBN Observational Constraints Under Extended Gravitational Dynamics

In this article, We investigate the cosmological consequences of a recently developed $f(R,G,\mathcal{T})$ gravitational framework, in which the action is formulated as a general function of the Ricci scalar $R$, the Gauss-Bonnet invariant $G$, and the trace of the energy-momentum tensor $\mathcal{T}$. As one of the most reliable probes of the physical conditions in the early universe, Big Bang nucleosynthesis offers a stringent framework for testing deviations from standard cosmology. We consider four representative models that are analyzed and constrained using observational limits on $\left|\Delta T_f/T_f\right|$ and the primordial helium mass fraction $Y_p$. The bounds obtained identify the allowed parameter regions for each model and demonstrate that significant departures from standard cosmology are compatible with nucleosynthesis observations. Our analysis shows that broad regions of the parameter space satisfy existing nucleosynthesis constraints, indicating the consistency of $f(R,G,\mathcal{T})$ gravity with the observed primordial light-element abundances and the established picture of the early universe preserving the observed abundances of light nuclei.

gr-qc↗

arXiv2026

Testing the Nature of Rotating Black Hole Shadows Surrounded by a Thin Accretion Disk within Rastall Gravity

We investigate the observational appearance of a rotating black hole (BH) in Rastall gravity by analyzing its shadow and accretion signatures under different illumination environments. The spacetime geometry is characterized by the Rastall parameter $\mu$, the structure parameter $\gamma$, and the rotation parameter $a$. To visualize the BH environment, we employ a ray-tracing algorithm that follows photon trajectories from the observer's screen to the emission region. We analyze how the shadow radius, distortion, and photon ring morphology respond to changes in the spacetime parameters. For a fixed value of $a$, the shadow observables exhibit a pronounced dependence on the Rastall gravity parameters. In particular, increasing the structure parameter $\gamma$ leads to a gradual enlargement of the shadow radius, indicating an expansion of the photon capture region surrounding the BH. At the same time, the distortion parameter decreases, implying that the shadow boundary becomes progressively more circular and less deformed. These results suggest that larger values of $\gamma$ tend to suppress the asymmetry induced by rotation and enhance the apparent size of the shadow. Similar modifications are observed for different values of the Rastall parameter $\mu$, demonstrating that the combined effects of $\mu$ and $\gamma$ leave distinct signatures on the shadow morphology. Consequently, shadow observations may provide an effective tool for constraining the parameter space of rotating BHs in Rastall gravity.

gr-qc↗

arXiv2026

Visual Characteristics of a Rotating Black Hole in $4$D Einstein-Gauss-Bonnet Gravity with Thin Accretion Disk Under EHT Constraints

This study investigates the visual characteristics of a rotating black hole (BH) within the fabric of $4$D Einstein-Gauss-Bonnet gravity illuminated with two illumination models, such as a celestial light sphere and a thin accretion disk. To visualize the BH shadow images, we use a recent fisheye camera model and ray-tracing method. And then, we focus on investigating the impact of the coupling parameter $\alpha$ and the spin parameter $a$ on the shadow images. The results exhibit that the shadow radius decreases, while the shadow deviation increases with the aid of $\alpha$. However, with respect to $a$, the shadow radius is slightly increased compared to the corresponding shadow deviation. For a celestial light sphere, the increasing values of $\alpha$, lead to a decrease in the corresponding photon ring, while the space-dragging effect becomes more prominent with increasing $a$. For a thin accretion disk, we enhance its inner edge to the BH event horizon, and the particle motion is different in the regions inside and outside the innermost stable circular orbit. The result demonstrates that the shadow becomes progressively asymmetric with $a$, while the overall size of the inner shadow gradually decreases with the variations of $\alpha$. Subsequently, we also investigated the distinct features of red-shift configurations on the disk for both direct and lensed images. Additionally, we used the latest observational data from M87* and Sgr A* to impose certain parameter constraints on $\alpha$; the results depict the consistency of our considering the BH model.

astro-ph.HE↗