arXiv subjects

Heena Ali

Publications and source records attributed to Heena Ali.

3 recordsLinked to original sources

arXiv2026

Testing loop quantum gravity through EHT observations of M87* and Sgr A* using rotating holonomy-corrected black holes

The Event Horizon Telescope (EHT) has provided a new tool for testing the strong-field regime of gravity by imaging the shadows of M87* and Sgr A*. These observations provide the first real opportunity to test whether quantum gravity--specifically loop quantum gravity--leaves observable imprints on spacetime. We use the EHT observations of M87* and Sgr A* to examine the observational signs of rotating holonomy-corrected black holes (RHCBHs). We discover that, in comparison to the typical Kerr black hole, the quantum correction parameter $b$ increases the size of the black hole shadow. As the deviation parameter $b$ increases in RHCBH, the prograde photon orbits shift outward, indicating a weaker effective gravitational field near the central region. Unlike Kerr naked singularities, which produce open arc-like shadows, the RHCBH spacetime can still produce closed shadow rings even in the absence of an event horizon. We find that photon rings continue to exist in the parameter range $b_E \leq b \leq b_p$, due to the presence of unstable circular photon orbits.We apply the Kumar--Ghosh method based on the shadow observables: the shadow area $A$ and the oblateness $D$ that together allow a unique determination of the spin parameter $a$ and the quantum correction parameter $b$. At $\theta_o=17$\textdegree~, the angular diameter bound of M87$^{*}$ yields $b \leq 0.1319\,M$ at $a = 0\,$ and $b \leq 0.421\,M$ at $a = 0.784\,M$, while at $\theta_o=50$\textdegree~, the angular diameter bound of Sgr A$^{*}$ yields $b \leq 0.5764\,M$ at $a = 0\,$ and $b \leq 0.7482\,M$ at $a = 0.6253\,M$ the Sgr~A$^{*}$. Our results show that nonzero values of the holonomy correction parameter are consistent with current EHT data, indicating that RHCBHs provide viable alternatives to the classical Kerr geometry in the strong-gravity regime and are strong astrophysical black hole candidates.

gr-qc↗

arXiv2025

Parameter estimation of Kerr-Bertotti-Robinson black holes using their shadows

We investigate the shadow of Kerr-Bertotti-Robinson black holes (KBRBHs), which have a deviation parameter $B$ that captures the effect of an external magnetic field on the spacetime geometry. These spacetimes of Petrov type $D$ are asymptotically non-flat. We utilise the separability of the Hamilton-Jacobi equation to generate null geodesics and examine the crucial impact parameters for unstable photon orbits that define the black hole shadow. We carefully investigate how the magnetic field strength $B$ and spin parameter $a$ influence black hole shadows, discovering that increasing $B$ increases the shadow size while also introducing additional distortions, especially at high spins. We calculate the shadow observables, viz., area $A$ and oblateness $D$ and create contour plots in the parameter space $(a, B)$ to facilitate parameter estimation. We also investigate the dependence of the shadow on the observer's position, specifically by altering the radial coordinate $r_O$ and the inclination angle $\theta$. For far viewers, the shadow approaches its asymptotic shape, but finite-distance observers perceive substantial deviations. The energy emission rate analysis reveals that the magnetic field parameter $B$ modifies the Hawking radiation spectrum, with increasing $B$ suppressing emission via backreaction, which lowers the Hawking temperature. Our findings confirm that KBRBH shadows encode imprints of magnetic deviations, thereby offering a potential avenue to distinguish Kerr from non-Kerr spacetimes and to probe magnetic effects in the strong-gravity regime.

gr-qc↗

arXiv2024

Shadows and parameter estimation of rotating quantum corrected black holes and constraints from EHT observation of M87* and Sgr A*

The scarcity of quantum gravity (QG) inspired rotating black holes limits the progress of testing QG through Event Horizon Telescope (EHT) observations. The EHT imaged the supermassive black holes, Sgr A* and M87*, revealing an angular shadow diameter of $d_{sh} = 48.7 \pm 7 \mu$as with a black hole mass of $M = 4.0_{-0.6}^{+1.1} \times 10^6 M\odot$ for Sgr A*. For M87*, with a mass of $M = (6.5 \pm 0.7) \times 10^9 M_\odot$, the EHT measured an angular diameter of $\theta_d = 42 \pm 3 \mu$as. We present rotating quantum-corrected black hole (RQCBH) spacetimes with an additional QC parameter $\alpha$ and constrain it by EHT observations. For angular shadow diameter ($d_{sh}$) of Sgr A* at $\theta_o = 50^0$, the bounds are $0.0 \leq \alpha \leq 1.443 M^2$ and $a \in (0, 0.8066 M)$. For $\theta_o = 90^0$, the bounds are $0.0 \leq \alpha \leq 1.447 M^2$ and $a \in (0, 0.894 M)$. While for M87* at inclination $\theta_o = 17^0$, the bounds are $a \in (0, 0.8511 M)$ at $\alpha=0$ and $a \in (0, 0.6157 M)$ at $\alpha=0.8985 M^2$. For $\theta_o = 90^0$, the bounds are $a \in (0, 0.8262 M)$ at $\alpha=0$ and $a \in (0, 0.9799 M)$ at $\alpha=0.4141 M^2$. These results show that $\alpha$ significantly affects the shadows, offering key constraints on QG models. With EHT constraints from Sgr A and M87*, RQCBHs and Kerr black holes are indistinguishable in much of the EHT-constrained parameter space, making RQCBHs strong candidates for astrophysical black holes along with other BHs, e.g., regular black holes and other quantum-corrected solutions.

gr-qc↗