Imaging black holes and jets with a VLBI array including multiple space-based telescopes

Abstract

Very long baseline interferometry (VLBI) from the ground at millimeter wavelengths can resolve the black hole shadow around two supermassive black holes, Sagittarius A* and M87. The addition of modest telescopes in space would allow the combined array to produce higher-resolution, higher-fidelity images of these and other sources. This paper explores the potential benefits of adding orbital elements to the Event Horizon Telescope. We reconstruct model images using simulated data from arrays including telescopes in different orbits. We find that an array including one telescope near geostationary orbit and one in a high-inclination medium Earth or geosynchronous orbit can succesfully produce high-fidelity images capable of resolving shadows as small as 3 µas in diameter. One such key source, the Sombrero Galaxy, may be important to address questions regarding why some black holes launch powerful jets while others do not. Meanwhile, higher-resolution imaging of the substructure of M87 may clarify how jets are launched in the first place. The extra resolution provided by space VLBI will also improve studies of the collimation of jets from active galactic nuclei.

THEZA: TeraHertz Exploration and Zooming-in for Astrophysics

“…The concept of multi-element space-borne interferometer has been also considered by [27]. Their concept differs from the EHI in the choice of orbits, number of space-borne antennas and the overall interferometric configuration of the system.…”

Space VLBI: from first ideas to operational missions

“…That said, the presence of the H-maser on board the RadioAstron spacecraft made it possible to conduct the ad hoc Gravitational Redshift Experiment (Litvinov et al, 2018;Nunes et al, 2019). Future advanced SVLBI systems operating at millimetre and sub-millimetre wavelengths (Andrianov et al, 2019;Fish et al, 2019;Kudrishov et al, 2019;Linz et al, 2019;Roelofs et al, 2019) might require new approaches to space-borne telescope heterodyning.…”

“…Several pre-design studies addressed mm-SVLBI issues over the past two decades: ARISE (Ulvestad, 2000), VSOP-2 (Hagiwara et al, 2009) (Part 2) and Millimetron (Kardashev et al, 2015). The current Special Issue presents the current status of Millimetron (Andrianov et al, 2019) and several new concepts (Fish et al, 2019;Linz et al, 2019;Kudrishov et al, 2019). All these concepts face many engineering challenges.…”

Black hole parameter estimation with synthetic Very Long Baseline Interferometry data from the ground and from space

“…Also, a ground-based imaging array at frequencies higher than about 345 GHz is extremely challenging due to strong attenuation and turbulence introduced by water vapor in the troposphere. A space-based array could overcome these limitations and potentially increase the array resolution by an order of magnitude (Roelofs et al 2019;Fish et al 2020), or provide fast uv-coverage suitable for dynamical imaging of variable sources like Sgr A* (Palumbo et al 2019). For this work, we consider the Event Horizon Imager (EHI) concept (Martin-Neira et al 2017;Kudriashov et al 2019;Roelofs et al 2019), which is a purely space-based interferometer consisting of two or three satellites in Medium Earth Orbits.…”

“…Synthetic data tools have been developed and used to predict the imaging performance of the EHT (e.g. Fish & Doeleman 2010;Falcke et al 2010;Lu et al 2014;Chael et al 2016;Johnson et al 2017;Bouman et al 2018;Roelofs et al 2020) and Space VLBI arrays (Roelofs et al 2019;Palumbo et al 2019;Fish et al 2020). However, image comparisons are challenging to quantify except for simple metrics evaluating pixel-by-pixel differences or cross-correlations, which do not always match a quality assessment by eye where a person looks at the reconstruction of certain model features, like a photon ring or extended jet.…”