Faculty of Science
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Event Horizon Imager

This project is devoted to the design of an instrument for high-resolution imaging of the shadows of supermassive black holes. A preliminary study is ongoing.

The mission concept aims for an angular resolution of ~5 micro-arcseconds, which opens up possibilities of high-precision tests of general relativity and other theories of gravity, high-precision measurements of black hole parameters like mass and spin, and an increased understanding of the behavior of the accreting plasma near the event horizon. Other science cases, including imaging of water in planet-forming disks, are considered as well.

For the desired resolution of 5 micro-acrseconds, the required distance between the telescopes (the baseline length) is over 2 times larger than our planet's diameter, at an observing frequency of ~0.5 THz. This high frequency has the additional advantage of strongly mitigating scattering by interstellar electrons in the Galactic plane, which distorts the observed image. Because, additionally, atmospheric effects make such high-frequency observations extremely challenging to perform from the ground, a fully space-based array observing at ~0.5 THz and utilizing very long baselines is considered.

With dish antennas limited to ~4 m in diameter by launch vehicle dimensions, both the required integration time for detections and imaging timescales for obtaining high-quality images are challenging. The design therefore follows the concept of interferometry using antennas on boards satellites placed in Polar Medium Earth Orbits involving inter-satellite laser links for data transmission and ranging, GNSS satellites for positioning, low-frequency observation channels for comparison with Earth-based observations and fringe detection bootstrapping, and a `local oscillator connection' between the satellites for clock synchronization. This concept also calls for an accurate reconstruction of the satellite orbits, which aids in detections.

Current studies include simulations of the source flux and structure as well as imaging performance in several frequency bands, studies on the technical feasibility of the critical components of the interferometer, studies into the requirements for the interferometer sub-systems, and studies into the achievable system performance. We built and tested in ESA`s lab a breadboard for experimental investigation of the achievable coherence. We concluded that the coherence requirement is satisfied with ample margin of 11 times. We were involved in a postdoctoral study with ESA and in an industrial study for precise satellite navigation in Medium Earth Orbits with GMV.

Papers on the candidate mission concept (2021), the system (2019) and its design (2019) are available over links 1, 2 and 3, respectively. This is Universe Today article about the mission concept. Paper on coherence achieved by breadboard Local Oscillator has been published open-access by JAI in 2021. The paper on imaging simulations of the Event Horizon Imager (2019) is available here; a press release on this paper can be found here, and media articles featuring this concept include Space dot compopular mechanics, and Phys.org.

See also the space VLBI workshop#1 `science' in NL 2018, and workshop#2 `technology' in USA 2020.

The project benefits from the support of ESTEC-ESA microwave lab of the TEC Directorate, JIVE [NL], and the industrial enterprises GMV Innovating Solutions [GB], DAS Photonics [ES], SpaceForest [PL], AXTAL GmbH [DE],  Orolia [FR], Marki Microwave [USA], and RPG Radiometer Physics GmbH [DE]. The project logo has been adapted from this paper.

The science PI is Heino Falcke. The technology PI is Manuel Martin-Neira. Studies are also performed by Volodymyr Kudriashov, Freek Roelofs and Christiaan Brinkerink.