Extended Gravity and Black Hole Shadows: Rotation Accounting

TL;DR

This paper derives rotating black hole solutions in extended gravity theories and analyzes their shadows, demonstrating how these theories can modify the effect of rotation and potentially be constrained by observational data.

Contribution

It introduces new rotating black hole solutions in specific extended gravity models using an improved Newman-Janis algorithm and links shadow observations to model constraints.

Findings

Horndesky and Gauss-Bonnet models weaken rotation effects.

Bumblebee model enhances rotation effects.

Shadow profiles can constrain extended gravity parameters.

Abstract

We obtain black hole rotating solutions for Horndesky theory (specific partial case), bumblebee model and Gauss-Bonnet scalar gravity using the specially improved Newman-Janis algorithm. The shadow profiles for these metrics were calculated. Applying the limitations from the Event Horizon Telescope we find the opportunity to constrain model parameters from considered extended gravity theories. We show that for three considered models two of them (Horndesky theory and Gauss-Bonnet scalar gravity) weaken the effect of rotation and bumblebee model enhances it. This conclusion matches the previously obtained one that extended gravity theories by themselves correct the effect of rotation in both directions.