arXiv subjects

Balendra Pratap Singh

Publications and source records attributed to Balendra Pratap Singh.

10 recordsLinked to original sources

arXiv2026

Analysis of Solar Flare and Sunspots on 4th Jan 2025 and Their Effects on Space Weather

Solar flares and coronal mass ejections (CMEs) are among the most energetic phenomena in the solar system, often impacting space weather and terrestrial technologies. In this study, we utilize SunPy, an open-source Python library for solar physics, to analyze solar active regions and their correlation with flare and CME events observed on 4th January 2025. Data from GOES, SDO (AIA and HMI), Solar Oribter (STIX), e-CALLISTO, Aditya L1 (SUIT), and SOHO are processed to track flare intensity, active region evolution, shock wave and CME dynamics. The analyzed flare is identified as an X1.8-class event, and our study highlights key magnetic precursors that led to it. This work enhances understanding of solar eruption precursors and supports future predictive models for space weather forecasting.

astro-ph.SR↗

arXiv2025

Thermodynamics and Shadows of Kerr black holes endowed with a global monopole charge

In this article, we present the thermodynamic and shadow properties of rotating black holes with global monopole charge. The angular diameter of Sgr A$^{*}$ black hole is 48.7 $\pm$ 7 $μas$, which is 8 $kps$ far away having a mass of $M = 4.0_{-0.6}^{+1.1} \times 10^6 M\odot$ as observed by Event Horizon Telescope and for the M87 black hole, the observed angular diameter is $θ_d = 42 \pm 3 μ$as, which is almost $16$ $Mpc$ far away with a mass of $M = (6.5 \pm 0.7) \times 10^9 M_\odot$. The global monopole charge parameter $α$ strongly affects the shape and size of the black hole shadow. We derived all the necessary equations to obtain the angular diameter of the rotating black hole shadow with the effect of the global monopole charge parameter $α$. For $α$ $\in$ (0, 0.08) with $a$ $\in$ $(0.7 M, 0.99 M)$, the angular diameter of M87 black hole shadow varies from $39$ $μas$ to $51$ $μas$. The angular diameter of Sgr A$^{*}$ black hole with global monopole charge parameter $α$ $\in$ (0, 0.04) and $a$ $\in$ $(0.7 M, 0.99 M)$, varies from $50$ $μas$ to $55$ $μas$. For bound values of $α$ and $a$, our results are consistent with the EHT observations.

gr-qc↗

arXiv2024

Black Hole Evaporation Process and Tangherlini-Reissner-Nordström Black Holes Shadow

In this article, we study the black hole evaporation process and shadow property of the Tangherlini-Reissner-Nordström (TRN) black holes. The TRN black holes are the higher-dimensional extension of the Reissner-Nordström (RN) black holes and are characterized by their mass $M$, charge $q$, and spacetime dimensions $D$. In higher-dimensional spacetime, the black hole evaporation occurs rapidly, causing the black hole's horizon to shrink. We derive the rate of mass loss for the higher-dimensional charged black hole and investigate the effect of higher-dimensional spacetime on charged black hole shadow. We derive the complete geodesic equations of motion with the effect of spacetime dimensions $D$. We determine impact parameters by maximizing the black hole's effective potential and estimate the critical radius of photon orbits. The photon orbits around the black hole shrink with the effect of the increasing number of spacetime dimensions. To visualize the shadows of the black hole, we derive the celestial coordinates in terms of the black hole parameters. We use the observed results of M87 and Sgr A$^{*}$ black hole from the Event Horizon Telescope and estimate the angular diameter of the charge black hole shadow in the higher-dimensional spacetime. We also estimate the energy emission rate of the black hole. Our finding shows that the angular diameter of the black hole shadow decreases with the increasing number of spacetime dimensions $D$.

gr-qc↗

arXiv2023

Shadows of quintessential dark energy black holes in the domain of outer communication

The rotating black holes in the quintessential dark energy correspond to three horizons: inner, outer, and quintessential horizon. The domain of outer communication is the region between outer and quintessential horizon. Here, in this work we study the photon region and shadows of the quintessential dark energy black holes when the observer stays statically in the domain of outer communication. The quintessential dark energy black holes shadow characterizes by its mass $(M)$, spin parameter $(a)$, quintessential dark energy parameter $(ω_q)$, and normalization factor $(γ)$. The dark energy parameter $ω_q$ can take values in between $-1.1<ω_q<-1/3$ and follows the equation of state $ω_q$=pressure$(p)$/energy density($ρ_q)$. This state parameter significantly affects the shape and size of the black hole shadow. We generalize all the geodesic equations of motion for $ω_q$ and obtain relation to visualize the black hole shadow by a static observer at any arbitrary distance in the domain of outer communication. We analytically estimate the black hole shadow observables: radius $R_s$, distortion parameter $δ_s$ and the shadow area $A$. Using the numerical values of shadow radius $R_s$ and area $A$, we obtain the angular diameter of the black hole shadow. The angular size of the M87 and Sgr A$^*$ black holes are $\ 42 \pm 3 μa s$ and $48.7 \pm 7 μa s $ respectively as observe by Event Horizon Telescope (EHT). In this case, the angular diameter of the black hole shadow increases with the quintessence parameter $ω_q$ and takes values $θ_d \approx 20 \pm 3{^o}$ with the parameter $-0.66 \leq ω_q \leq -0.62$ for the static observer at $r_o=5M$ in the domain of outer communication.

gr-qc↗

arXiv2022

Rotating regular black holes in AdS spacetime and its shadow

The presence of a photon region around the black hole is an essential feature in receiving the emitted spectrum from the vicinity of the black hole by the distant observer. In this paper, we investigate the optical properties of rotating regular anti-de Sitter (AdS) black holes, which characterized by its mass $(M)$, spin parameter $(a)$, deviation parameter $(k)$ and the cosmological constant $(Λ)$ related to the curvature radius via $(Λ=-3/l^2)$. We derive the complete null geodesic equations of motion and study the unstable circular orbits for an observer at given Boyer-Lindquist coordinates ($r_O,\;\vartheta_O$) in the domain of outer communication and trace the photon rings. For the analytical part of our study, we investigate the observables, namely, shadow radius $(R_s)$ and distortion parameter $(δ_s)$. These rotating regular AdS black holes have smaller shadows when compare to the Kerr and regular spacetimes. We also estimate the energy emission rate of the black hole.

gr-qc↗

arXiv2022

Rotating charged black holes shadow in quintessence

We study the shadow of rotating charge black holes in the presence of quintessence. The shadow of a rotating black hole is a distorted circle and in our study, we find that the shape and size of the black hole shadow depend upon four parameters, i.e., charge $q$, spin parameter $a$, quintessential field parameter $ω_q$ and normalization factor $c$. The parameter $ω_q$ can take the value between $-1<ω_q<-1/3$ and related with pressure $p$ and density $ρ_q$ by the equation of state $p=ω_q ρ_q$. We derive the complete geodesic structure of photon near black hole using the Hamilton-Jacobi equation and Carter constant separable method. We relate celestial coordinate to geodesics equation and plot the contour of the black hole shadow for the case $ω_q=-2/3$. We compare our results with the standard Kerr-Newman black hole and find that for a fix value of $a$ and $q$, the black hole shadow decreases and get distorted with $c$. The area of the photon sphere is equal to the high-energy absorption cross section due to the optical properties of the black hole. On the basis of this assumption we calculate the energy emission rate of the black hole.

gr-qc↗

arXiv2021

Shadows of black hole surrounded by anisotropic fluid in Rastall theory

Due to the gravitational lensing effect, a black hole casts a shadow larger than its horizon over a bright background, and the shape and size can be calculated. The Event Horizon Telescope collaboration has produced the first direct image (shadow) of the black hole and it is in accordance with the shadow of a Kerr black hole of general relativity. However, deviations from the Kerr black hole arising from modified theories of gravity are not ruled out and they are important as they offer an arena to test these theories through astrophysical observation. This stimulates us to investigate rotating black holes surrounded by anisotropic fluid in Rastall theory namely a rotating Rastall black hole, which is characterized by mass $M$, spin $a$, field structure parameter $N_s$ and the Rastall parameter $ψ$. It encompasses, as special cases, Kerr ($N_s \to 0$) and Kerr-Newman ($s=0$ and $N_s = -Q^2 $) black holes. The rotating Rastall black hole is characterized by an additional cosmological-like horizon apart from Cauchy and event horizons. We derive an analytical formula for the shadow of a rotating Rastall black hole and go on to visualize the shadow of black holes for various values of the parameters for an observer at a given coordinate ($r_O, θ_O$) in the domain $[r_+,r_q]$.

gr-qc↗

arXiv2020

Shadow and deflection angle of rotating black hole in asymptotically safe gravity

We analytically investigate the shadows cast by rotating black holes in the asymptotically safe gravity (ASG) by deriving complete null geodesics and observables using the Hamilton-Jacobi equation and Carter separable method. It turns out that the apparent shape and size of the shadow depend on the ASG parameters ($ζ, γ$) in addition to other black hole parameters ($M, a$). The size of black hole shadows monotonically decreases and shadows get more distorted with increasing values of ASG parameters when compared with the Kerr black hole shadows. In turn, we use shadow observables to estimate black hole spin and ASG parameters. Noteworthy, we find that the deflection angle of the light has been modified by ASG parameters to generalize the Kerr deflection angle, and the corrections in the deflection angle are of $\mathcal{O}(μ$as). In the vanishing limits of ASG parameters, our results smoothly reduced to the Kerr black holes. The inferred circularity deviation $ΔC\leq 0.10$ for the M87* black hole shadow merely constrains the ASG parameter $ζ$, however, shadow angular diameter $θ_d=42\pm 3\, μ$as, within the $1σ$ region, places bounds $ζ\leq 0.1324$ for $γ=0.10$.

gr-qc↗

arXiv2018

Shadows of rotating five-dimensional charged EMCS black holes

Higher dimensional theories admit astrophysical objects like supermassive black holes, which are rather different from standard ones, and their gravitational lensing features deviate from general relativity. It is well known that a black hole shadow is a dark region due to the falling geodesics of photons into the black hole and, if detected, a black hole shadow could be used to determine which theory of gravity is consistent with observations. Measurements of the shadow sizes around the black holes can help to evaluate various parameters of the black hole metric. We study the shapes of the shadow cast by the rotating five-dimensional charged Einstein-Maxwell-Chern-Simons (EMCS) black holes, which is characterized by the four parameters, i.e., mass, two spins, and charge, in which the spin parameters are set equal. We integrate the null geodesic equations and derive an analytical formula for the shadow of the five-dimensional EMCS black hole, in turn, to show that size of black hole shadow is affected due to charge as well as spin. The shadow is a dark zone covered by a deformed circle, and the size of the shadow decreases with an increase in the charge $q$ when compared with the five-dimensional Myers-Perry black hole. Interestingly, the distortion increases with charge $q$. The effect of these parameters on the shape and size of the naked singularity shadow of five-dimensional EMCS black hole is also discussed.

gr-qc↗

arXiv2017

Shadow of Schwarzschild-Tangherlini black holes

We study the shadow cast by the H$D$ Schwarzschild-Tangherlini black hole, and analytically calculate the influence of extra dimensions on the shadow of a black hole. A black hole casts a shadow as an optical appearance because of its strong gravitational field which is known to be a dark zone covered by a circle for a Schwarzschild black hole. We demonstrate that the null geodesic equation can be integrated by Hamilton-Jacobi approach, which enables us to investigate the shadow cast by the H$D$ Schwarzschild-Tangherlini black holes. Interestingly, it turns out that, for fixed values of the mass parameter, the shadow in H$D$ spacetimes are smaller when compared with 4$D$ Schwarzschild black hole. Further, the shadows of H$D$ Schwarzschild-Tangherlini black holes are concentric circles with a radius of the circle decreases with increase in $D$. We visualize the photon regions and the shadows in various dimensions for different values of the parameters, and the energy emission rates are is also investigated. Our results, in the limit $D=4$, reduced exactly to \emph{vis-$\grave{a}$-vis} Schwarzschild black hole case.

gr-qc↗