Comment on "Strong lensing and shadow of Ayon-Beato-Garcia (ABG) nonsingular black hole"

Abstract

A recent article (Ramadhan et al. Eur Phys J C 83:465, 2023) suggested that the Sagittarius A* black hole cannot be modeled by an Ayon-Beato-Garcia regular black hole due to the incompatible shadow radius. However, they overlooked the distant-observer limit of the correction term in the effective geometry, which renders their calculation invalid. When evaluated correctly, the result reverses the conclusion of the paper. This comment highlights the flaw and demonstrates how to properly compute the shadow radius of such a black hole model using elementary geometry.

Figures (2)

• Figure 1: The geometric setup for calculating the BH shadow radius, $R_{sh}$. The black filled circle represents the event horizon of the BH, and the red circle around it denotes the photon sphere. The red dot at $r_O$ marks the observer’s location.
• Figure 2: The shadow radius obtained from Eq. \ref{['eq. rsh bc sqrt3']} (blue curve) and that presented in Ref. Ramadhan:2023ogm (magenta curve), shown together with the $1\sigma$ and $2\sigma$ constraints from the Sagittarius A* BH. The black dashed line represents the shadow radius of a Schwarzschild BH.