Shadows near supermassive black holes: from a theoretical concept to GR test

TL;DR

This paper discusses the evolution of black hole shadow studies from a theoretical idea to a practical tool for testing general relativity in strong gravitational fields, highlighting observational confirmations.

Contribution

It reviews the development of black hole shadow research and its role in testing GR beyond weak-field approximations.

Findings

Black hole shadows have been observed around Sgr A* and M87*.

Observational data supports the existence of supermassive black holes.

Black hole shadow studies provide strong tests of general relativity.

Abstract

General relativity (GR) passed many astronomical tests but in majority of them GR predictions have been tested in a weak gravitational field approximation. Around 50 years ago a shadow has been introduced by J. Bardeen as a purely theoretical concept but due to an enormous progress in observational and computational facilities this theoretical prediction has been confirmed and the most solid argument for an existence of supermassive black holes in Sgr A* and M87* has been obtained.