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The Event Horizon Telescope (EHT) - a planet-scale array of eight ground-based radio telescopes forged through international collaboration - was designed to capture black hole images. On April 10, 2019, in coordinated press conferences across the globe, EHT researchers revealed that they successfully, unveiled the first direct visual evidence of a supermassive black hole and its shadow. This provides strong evidence regarding the validity of Einstein's general theory of relativity and the existence of a supermassive black hole in the center of a galaxy. This breakthrough was announced on April 10, 2019, in a series of six papers published in a special issue of The Astrophysical Journal Letters.

The EHT collaboration involves more than 200 researchers from Africa, Asia, Europe, North and South America. The collaboration is working to capture the most detailed black hole images ever by creating a virtual Earth-sized telescope. Supported by considerable international investment, the EHT links existing telescopes using innovative systems - creating a fundamentally new, unprecedented instrument with the highest angular resolving power that has yet been achieved.

Japanese researchers contributed to various aspects of this research. The ALMA Telescope, one of the eight telescopes found in the EHT, is the most sensitive telescope of the EHT additionally, The National Astronomical Observatory of Japan (NAOJ) developed a data transmission instrument for ALMA to deliver the vast amount of data taken with the telescopes to its base facility. Japan, together with Asian partners, established the East Asian Observatory, which operates the James Clark Maxwell Telescope at Maunakea, Hawai`i.

"We also contributed to software," said Mareki Honma, Professor and Director of NAOJ Mizusawa VLBI Observatory. "We adopted a new method called 'sparse modeling' in the imaging software. It enabled us to obtain a reliable image from limited data. The EHT collaboration established four independent teams for imaging and the teams employed three different methods to generate the final images. In the end, all the teams obtained nearly identical images of the black hole."

"We also contributed to theory," said Kenji Toma, Associate Professor of Frontier Research Institute for Interdisciplinary Sciences in Tohoku University. "The EHT collaboration theory team, including several Japanese researchers and me, constructed a large library of models based on Einstein's general theory of relativity as well as plasma physics."

"The team compared the observed data with this library and confirmed that the observed ring image is consistent with expectations of the spinning black hole shadow, as predicted by the general theory of relativity. M87 has a powerful jet, for which the Japanese researchers have long been developing a theoretical model. This knowledge was very helpful for constraining the models for the observed ring image."

Publication Details:

Title: First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
Authors:The Event Horizon Telescope Collaboration, Kazunori Akiyama, Antxon Alberdi, Walter Alef, Keiichi Asada, Rebecca Azulay, Anne-Kathrin Baczko, David Ball, Mislav Baloković, Kenji Toma, et al.
Journal: The Astrophysical Journal Letters
DOI: https://doi.org/10.3847/2041-8213/ab0ec7

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