Disentangling photon rings beyond General Relativity with future radio-telescope arrays

TL;DR

This paper investigates how future radio-telescope arrays could detect modifications in black hole images caused by new physics beyond General Relativity, focusing on the potential to resolve multiple photon rings.

Contribution

It introduces synthetic models of black hole images with two rings and analyzes detection prospects with upgraded and space-based radio telescopes using super-resolution.

Findings

Current arrays cannot detect second rings in motivated parameter regions.

Upgrading with Earth-based telescopes improves detection sensitivity.

Adding space-based stations and super-resolution techniques enhances detection capabilities.

Abstract

New physics beyond General Relativity can modify image features of black holes and horizonless spacetimes and increase the separation between photon rings. This motivates us to explore synthetic images consisting of two thin rings. Our synthetic images are parameterized by the separation as well as the relative flux density of the two rings. We perform fits to the visibility amplitude and analyze closure quantities. The current Event Horizon Telescope array cannot detect the presence of a second ring in the region of parameters motivated by particular new-physics cases. We show that this can be improved in three ways: first, if the array is upgraded with Earth-based telescopes with sufficiently high sensitivity, second, if the array is upgraded with a space-based station and third, if super-resolution techniques are used for the data obtained by the array.