Orbital configurations of spaceborne interferometers for studying photon rings of supermassive black holes

TL;DR

This paper explores optimal orbital configurations for spaceborne interferometers to study photon rings of supermassive black holes, aiming to significantly improve resolution over Earth-based telescopes like the EHT.

Contribution

It presents preliminary mission designs and orbit configurations for a space interferometer system focused on photon ring detection and analysis.

Findings

Orbit configurations can achieve an order of magnitude better resolution than EHT.

Space interferometers enable detailed surveys of supermassive black holes.

The system allows robust tests of strong gravity through photon ring observations.

Abstract

Recent advances in technology coupled with the progress of observational radio astronomy methods resulted in achieving a major milestone of astrophysics - a direct image of the shadow of a supermassive black hole, taken by the Earth-based Event Horizon Telescope (EHT). The EHT was able to achieve a resolution of $\sim$20 $\mu$as, enabling it to resolve the shadows of the black holes in the centres of two celestial objects: the supergiant elliptical galaxy M87 and the Milky Way Galaxy. The EHT results mark the start of a new round of development of next generation Very Long Baseline Interferometers (VLBI) which will be able to operate at millimetre and sub-millimetre wavelengths. The inclusion of baselines exceeding the diameter of the Earth and observation at as short a wavelength as possible is imperative for further development of high resolution astronomical observations. This can be achieved by a spaceborne VLBI system. We consider the preliminary mission design of such a system, specifically focused on the detection and analysis of photon rings, an intrinsic feature of supermassive black holes. Optimised Earth, Sun-Earth L2 and Earth-Moon L2 orbit configurations for the space interferometer system are presented, all of which provide an order of magnitude improvement in resolution compared to the EHT. Such a space-borne interferometer would be able to conduct a comprehensive survey of supermassive black holes in active galactic nuclei and enable uniquely robust and accurate tests of strong gravity, through detection of the photon ring features.