Imaging the event horizon of M87* from space on different timescales

Abstract

Context. The concept of a new space very long baseline interferometry (SVLBI) system named the Event Horizon Imager (EHI) has been proposed to dramatically improve black hole imaging and provide precise tests of the theory of general relativity. Aims. This paper presents imaging simulations for the EHI. We investigate the ability to make high-resolution movies of the black hole shadow and jet launching region around the supermassive black hole M87* and other black hole jets with a three-satellite EHI configuration. We aim to identify orbital configurations to optimize the uυ-coverage to image variable sources. Methods. Observations of general relativistic magnetohydrodynamics (GRMHD) models were simulated for the configuration, consisting of three satellites in circular medium earth orbits with an orbital plane perpendicular to the line of sight. The expected noise was based on preliminary system parameters. Movie frames, for which a part of the uυ-coverage may be excessively sparse, were reconstructed with algorithms that recover missing information from other frames. Averaging visibilities accumulated over multiple epochs of observations with an appropriate orbital configuration then improves the image quality. With an enhanced signal-to-noise ratio, timescales of observed variability were decreased. Results. Our simulations show that the EHI with standard system parameters is capable of imaging the variability in the M87* environment on event horizon scales with approximately a month-long temporal resolution. The EHI with more optimistic noise parameters (enhancing the signal-to-noise ratio about 100-fold) would allow for imaging of the variability on gravitational timescales. Observations with an EHI setup at lower frequencies are capable of imaging the variability in extended jets. Conclusions. Our study shows that the EHI concept can be used to image the variability in a black hole environment and extended jets, allowing for stronger tests of gravity theories and models of black hole accretion, plasma dynamics, and jet launching.