Shadow of a black hole at cosmological distance

TL;DR

This paper develops an approximate method to calculate black hole shadow sizes in expanding universes, accounting for cosmic components like matter, radiation, and dark energy, revealing how distant supermassive black holes' shadows relate to local ones.

Contribution

It introduces a new angular size redshift relation-based approach for shadow size calculation in multicomponent expanding universes, extending beyond simple Schwarzschild-de Sitter models.

Findings

Supermassive black hole shadows at large distances can resemble local black hole shadows.

The method applies to universes with matter, radiation, and dark energy components.

Sensitivity limits for observing distant black hole shadows are discussed.

Abstract

Cosmic expansion is expected to influence on the size of black hole shadow observed by comoving observer. Except the simplest case of Schwarzschild black hole in de Sitter universe, analytical approach for calculation of shadow size in expanding universe is still not developed. In this paper we present approximate method based on using angular size redshift relation. This approach is appropriate for general case of any multicomponent universe (with matter, radiation and dark energy). In particular, we have shown that supermassive black holes at large cosmological distances in the universe with matter may give a shadow size approaching to the shadow size of the black hole in the center of our galaxy, and present sensitivity limits.