Tianyou Ren | Searcharxiv

arXiv2026

Radiation properties of a regular black hole embedded in a Dehnen-type dark matter halo with a thin accretion disk

We investigate the shadow, timelike geodesic structure, radiation properties of thin accretion disks, and optical appearance of a static spherically symmetric regular black hole, constructed based on the Dehnen-type density profile. Using observational data from M87* and Sgr A*, we constrain the model parameter $a$ at both $1\sigma$ and $2\sigma$ confidence levels. Based on the Page--Thorne model, we calculate the local radiative flux, redshift factor distribution, and the radiation flux received by a distant observer, systematically examining the effects of the parameter $a$ and the viewing angle on the black hole image. The results show that larger $a$ will enlarge the effective radiation area of the accretion disk and significantly enhance the asymmetry and Doppler boosting effects of the direct and secondary images at large viewing angles.

gr-qc↗

arXiv2025

Spherically symmetric charged (anti-)de Sitter black hole in $f(R,T)$ gravity coupled with nonlinear electrodynamics

We investigate black hole solutions in quadratic $f(R,T)=R+kT^2$ gravity coupled with nonlinear electrodynamics $\mathcal{L}(F)=\alpha - F/(4\pi) + \gamma F^2$. Solving the field equations yields an exact magnetically charged (anti-)de Sitter black hole metric featuring novel $r^{-6}$ and $r^{-14}$ correction terms. The horizon structure can exhibit up to four horizons depending on the parameters. Thermodynamic analysis reveals that the heat capacity exhibits critical phase transitions, with the critical point significantly shifted by the coupled corrections. Using the effective metric formalism, we study the photon sphere and black hole shadow, finding that the magnetic charge $Q$ shrinks the shadow while the nonlinear parameter $\gamma$ enlarges it. Constraints from Event Horizon Telescope observations of M87* and Sgr A* place the parameter $\gamma$ at the order of $10^3$ at $1\sigma$ and $2\sigma$ confidence levels. Our results demonstrate that quadratic $f(R,T)$ gravity combined with nonlinear electrodynamics provides a consistent framework for strong-field gravity phenomenology.

gr-qc↗