arXiv subjects

Javokhir Sharipov

Publications and source records attributed to Javokhir Sharipov.

5 recordsLinked to original sources

arXiv2026

Magnetic Modification of Black Hole Photospheres with Image Contraction, Efficiency Shifts and Redshift Boosts in Schwarzschild-Bertotti-Robinson Spacetime

We investigate the optical and radiative signatures of an accretion disk around a Schwarzschild black hole (BH) immersed in a uniform magnetic field. The spacetime geometry is described by the Schwarzschild-Bertotti-Robinson (SBR) metric, which represents the non-rotating sector of the recently discovered Kerr-Bertotti-Robinson exact solution to the Einstein-Maxwell equations. We begin with the study of null geodesics and demonstrate that the self-consistent magnetic field fundamentally alters photon propagation, causing an expansion of light bundles relative to the Schwarzschild case due to modified initial conditions in the orbital equation. We then compute the magnetic field-dependent shifts of key characteristic radii: the event horizon ($r_h$), photon sphere ($r_{ph}$), and innermost stable circular orbit ($r_{ISCO}$). We find that all three increase monotonically with field strength $B$, revealing a magnetic amplification of the effective gravitational field. For $B=0.05$, we find that the lensed emission bands contract to a narrower impact parameter range, $b\in(4.976,5.149)\cup(5.19,6.128)$. Employing ray-tracing formalism, we construct observed accretion disk images and quantify magnetic modifications, showing that the direct image contracts while maximum energy flux, radiation temperature, and redshift factor are enhanced. Complementing these numerical findings, we develop an analytical framework for the accretion disk dynamics. We derive the modified Keplerian frequency $Ω_K$, along with the specific energy $E$ and angular momentum $L$ for circular orbits. From these, we obtain the exact ISCO radius $r_{\text{ISCO}}$, which shows an outward shift. This outward shift reveals that the radiative efficiency decreases dramatically with increasing magnetic field strength $B$. For $β= BM \sim 0.1$, the efficiency drops by approximately $91\%$.

gr-qc↗

arXiv2026

Optical Signatures of a Schwarzschild Black Hole in a Dehnen-Type Dark Matter Halo

In this paper, the optical effects that occur near a Schwarzschild-like black hole (BH) with a Dehnen-type $(1,4,2)$ dark matter (DM) halo are explored. We first derive the photon sphere radius and obtain an analytical expression for the deflection angle in the weak-field regime by applying the Gauss-Bonnet theorem (GBT). For the strong-field regime, we perform ray-tracing calculations to examine the behavior of light trajectories and determine the corresponding number of orbits. We further compute the BH shadow and gravitational lensing in a plasma medium and provide constraints arising from the DM halo parameters. We also extend our analysis to weak gravitational lensing within plasma environments, considering both uniform and singular isothermal sphere (SIS) distributions. We find the analytical expressions for the deflection angle in the presence of plasma and examine the resulting effects on image magnification. The overall results highlight how DM halo properties and plasma characteristics jointly alter observable lensing signatures.

gr-qc↗

arXiv2025

Nonlinear electrodynamic black holes and their role in testing modified theories of gravity

The nature of black holes (BHs) and their potential deviations from classical General Relativity (GR) remain central questions in modern astrophysics. Nonlinear electrodynamics (NED) offers a promising mechanism to construct regular BHs that avoid singularities while retaining key astrophysical features. In this work, we analyze NED-inspired BHs and derive constraints on the magnetic parameter using Bayesian parameter estimation from Event Horizon Telescope (EHT) observations. We obtain $q = 0.63 ^{+0.68}_{-0.44} \times 10^9 M_{\odot}$ for M87* and $q = 0.33 ^{+0.36}_{-0.23} \times 10^6 M_{\odot}$ for Sgr A*, affecting their horizon structure. A comparison with the Schwarzschild solution highlights deviations in geometry and horizon properties, emphasizing the impact of NED. We also examine observational signatures, including BH shadows and gravitational lensing. Using $R_{\text{sh}} = r_{\text{ph}} \sqrt{1/f(r_{\text{ph}})}$, we explore shadow features under uniform and non-uniform plasma conditions, revealing deviations from GR predictions due to NED effects. By analyzing photon sphere shifts and lensing patterns, we identify observable features that distinguish these BHs from classical ones. Our results suggest that NED-induced modifications may leave detectable imprints in strong-field regimes, opening pathways to test alternative gravity models. Future missions such as the Laser Interferometer Space Antenna (LISA) and next-generation X-ray observatories, along with ongoing observations from the EHT and gravitational wave detections by the Laser Interferometer Gravitational-Wave Observatory and Virgo (LIGO--Virgo), will be essential for refining constraints on such models.

gr-qc↗

arXiv2025

Periodic orbits and observational accretion disk around a Schwarzschild-like black hole surrounded by dark matter halo

In this work, we investigate the dynamics of periodic orbits and the properties of accretion disks around a Schwarzschild-like black hole (BH) immersed in a King-type dark matter (DM) halo. Our analysis focuses on how the presence of the King DM halo influences both the behavior of periodic orbits and the radiative characteristics of the accretion disk. We begin by examining time-like periodic geodesic orbits for various configurations characterized by different energy and angular momentum values, represented by the integers $(z, w, v)$. Furthermore, we explore the effects of the King DM halo on time-like periodic geodesics, marginally bound orbits, and innermost stable circular orbits, thereby providing a deeper understanding of how the DM halo environment modifies the behavior of these stable orbits and timelike particle geodesics. Finally, we analyze the null geodesics and the accretion disk properties by studying their direct and secondary images, redshift distributions, and radiation fluxes as observed at infinity for a range of inclination angles. This approach allows us to gain valuable insights into the spacetime geometry of a Schwarzschild-like BH within the King-type DM halo, its physical and radiative properties in the accretion disk, and the corresponding observational implications.

gr-qc↗

arXiv2025

Observable thin accretion disk around a self-dual black hole in loop quantum gravity

In this paper, we study a self-dual black hole (BH) in Loop Quantum Gravity (LQG), analyzing both timelike and null geodesics. Using observational data from Mercury's perihelion shift and the orbit of the S2 star around Sagittarius A$^{\star}$ (Sgr A$^{\star}$), we derive constraints on the polymeric function $P$. We further investigate photon trajectories near the self-dual BH under various scenarios to explore their observational relevance. Finally, we examine the properties of accretion disks around the self-dual BH in LQG, including their direct and secondary images, and study the redshift and the observed energy flux distribution across the accretion disk as measured by distant observers for different inclination angles. Our findings provide new insights into the physical nature and accretion properties of self-dual BHs in LQG and their possible observational consequences.

gr-qc↗