Testing Charged Black Holes Embedded in Anisotropic Matter and Surrounded by Plasma through Gravitational Lensing: Bounds from the Sloan Lens ACS Survey

Abstract

We investigate weak gravitational lensing by a charged black hole surrounded by anisotropic matter, described by the two-component Kiselev metric, and immersed in a homogeneous plasma. We first examine the black hole geometry and horizon structure and then derive the weak-deflection angle from the Hamiltonian description of light propagation in plasma, using an expansion with a fixed turning point that we verify against direct numerical integration. Using the gravitational lens equation, we obtain the Einstein-ring angle, the image positions, the total magnification and the fractional magnifications of the primary and secondary images. We then confront the model with the Einstein radii of two galaxy-scale lenses of the Sloan Lens ACS Survey, J0008$-$0004 and J0029$-$0055. Because the Einstein angle cannot be smaller than the reduced deficit deflection, the observed radii give the mass-independent bounds $K<6.5\times10^{-6}$ and $K<4.2\times10^{-6}$, respectively. The charge correction to the Einstein radius is suppressed by $r_s/R_E\approx 5\times10^{-6}$ and is unobservable, while the plasma parameter at the optical wavelengths of the SLACS imaging is of order $10^{-22}$ and cannot be constrained. Our results show that galaxy-scale strong lensing data place stringent limits on anisotropic matter surrounding the lens, whereas plasma effects can be probed only at low radio frequencies.