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Chinese Journal of Space Science ›› 2021, Vol. 41 ›› Issue (2): 211-233.doi: 10.11728/cjss2021.02.211

• Research Articles • Previous Articles     Next Articles

An Event Horizon Imager (EHI) Mission Concept Utilizing Medium Earth Orbit Sub-mm Interferometry

KUDRIASHOV V1, MARTIN-NEIRA M2, ROELOFS F1, FALCKE H1,3, BRINKERINK C1, BARYSHEV A4, HOGERHEIJDE M5,6, YOUNG A1, POURSHAGHAGHI H1, KLEIN-WOLT M1, MOSCIBRODZKA M1, DAVELAAR J1,7, BARAT I2, DUESMANN B2, VALENTA V2, PERDIGUES ARMENGOL J M2, DE WILDE D2, MARTIN IGLESIAS P2, ALAGHA N2, VAN DER VORST M2   

  1. 1 Department of Astrophysics/IMAPP, Radboud University Nijmegen, P. O. Box 9010, 6500 GL Nijmegen, the Netherlands;
    2 ESTEC/ESA, Keplerlaan 1, 2201 AZ Noordwijk, the Netherlands;
    3 Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, D-53121 Bonn (Endenich), Germany;
    4 University of Groningen, Landleven 12, 9747 AD Groningen, the Netherlands;
    5 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, Leiden, the Netherlands;
    6 Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, the Netherlands;
    7 Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA
  • Received:2020-08-20 Revised:2021-01-29 Online:2021-03-15 Published:2021-04-10
  • Supported by:
    The research work reported in the paper was partly supported by the Project NPI-552 "Space-to-space Interferometer System to Image the Event Horizon of the Super Massive Black Hole in the Center of Our Galaxy" co-funded by the European Space Agency (ESA) and the Radboud University of Nijmegen (ESA contract 4000122812), and by the NWO project PIPP "Breakthrough Technologies for Interferometry in Space".

Abstract: Submillimeter interferometry has the potential to image supermassive black holes on event horizon scales, providing tests of the theory of general relativity and increasing our understanding of black hole accretion processes. The Event Horizon Telescope (EHT) performs these observations from the ground, and its main imaging targets are Sagittarius A* in the Galactic Center and the black hole at the center of the M87 galaxy. However, the EHT is fundamentally limited in its performance by atmospheric effects and sparse terrestrial (u,v)-coverage (Fourier sampling of the image). The scientific interest in quantitative studies of the horizon size and shape of these black holes has motivated studies into using space interferometry which is free of these limitations. Angular resolution considerations and interstellar scattering effects push the desired observing frequency to bands above 500 GHz.
This paper presents the requirements for meeting these science goals, describes the concept of interferometry from Polar or Equatorial Medium Earth Orbits (PECMEO) which we dub the Event Horizon Imager (EHI), and utilizes suitable space technology heritage. In this concept, two or three satellites orbit at slightly different orbital radii, resulting in a dense and uniform spiral-shaped (u,v)-coverage over time. The local oscillator signals are shared via an inter-satellite link, and the data streams are correlated on-board before final processing on the ground. Inter-satellite metrology and satellite positioning are extensively employed to facilitate the knowledge of the instrument position vector, and its time derivative. The European space heritage usable for both the front ends and the antenna technology of such an instrument is investigated. Current and future sensors for the required inter-satellite metrology are listed. Intended performance estimates and simulation results are given.

Key words: Instrumentation, Space, VLBI, Radio Telescopes

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