Gravitational lensing and shadow around a non-minimally coupled Horndeski black hole in plasma medium

TL;DR

This paper explores how a non-minimally coupled Horndeski black hole's shadow and light deflection are affected by plasma environments, providing insights into observational signatures and parameter constraints.

Contribution

It presents an analytical study of light deflection and shadow features of a Horndeski black hole in plasma, including observational constraints from EHT data.

Findings

Plasma properties significantly influence the black hole shadow.

Constraints on Horndeski coupling are derived from shadow observations.

Black hole geometry affects plasma distribution and observable signatures.

Abstract

We investigate the light deflection and the shadow characteristics of a non-minimally coupled Horndeski black hole surrounded by a magnetized, cold, pressureless plasma medium, while considering both homogeneous and non-homogeneous plasma distributions. We consider an analytical expression for the deflection angle of light and analyze how it is influenced by the plasma properties and the Horndeski coupling constant. The circular light orbits, which define the photon sphere, are also analyzed for both types of plasma media, highlighting their impact on the shadow boundary. The shadow properties of the black hole are examined in detail, and constraints on the model parameters are derived by comparing the theoretical shadow radius with observational measurements of Sgr A* and M87* obtained by the Event Horizon Telescope Collaboration. We also study the black hole shadow images along with the corresponding intensity profiles produced by a radially infalling accretion flow in the plasma environment. The results are particularly interesting, as they reveal how the modified black hole geometry affects both the plasma distribution and the black hole parameters in a realistic astrophysical context.