Japan’s role in black hole image: Compiling data, filling in blanks

Japanese scientists and engineers compiled immense amounts of data and filled in gaps for the international effort that produced the first image of a black hole, hailed as the greatest science news this century.
In total, 207 scientists in 17 nations and regions took part in the project that led to the April 10 release of the image of the black hole from the M87 galaxy, about 55 million light years away.
The team included 22 Japanese scientists working both in Japan and overseas, and they were represented by Mareki Honma, a professor of astrophysics at the National Astronomical Observatory of Japan (NAOJ).
“For the first time since Einstein’s theory of relativity, the image provides visual evidence of a black hole,” Honma said. “It is a hugely significant image that proves beyond a doubt the existence of a black hole in the center of a galaxy.”
Eight radio telescopes in six locations around the globe played a central role in producing the image. The eight telescopes created a virtual telescope with an aperture of about 10,000 kilometers, close to the Earth’s diameter.
Although none of the NAOJ’s telescopes in Japan was used in the project, the Japanese scientists were tasked with pulling together the huge amount of scattered data recorded from those locations.
The ALMA telescope used in the project was installed at an altitude of about 5,000 meters in Atacama, northern Chile, in a very dry environment to prevent humidity from affecting the observations.
However, the low pressure at such an altitude often led to malfunctions in the hard drives used to record the observed data.
Members of the Japanese team installed optical transmission equipment developed by researchers at NAOJ and private-sector companies to allow for large data flows.
After repeated tests in Chile, the equipment worked effectively and was used to transmit the data from the ALMA telescope to another facility constructed at a lower altitude of about 2,900 meters at Atacama.
Japanese researchers also contributed to what can be considered the processing of the black hole image.
The distances between the eight telescopes used to observe the black hole created gaps in the data collected from those facilities. To produce a complete image of the black hole, additional work was needed to statistically deduce what laid in the gaps of data.
With the cooperation of mathematicians, the Japanese researchers developed a technology to obtain high-quality images even with a minimal amount of data.
Two similar technologies were also used to produce three different images. Because all three images were the same, the project participants became increasingly confident that the image they had captured was from the black hole.
Honma explained that technology used for magnetic resonance imaging of patients at medical institutions was adapted from around 2010 to develop the new telescope processing technology.
Ken Ohsuga, a professor of theoretical astrophysics at the University of Tsukuba, said of the image: “The achievement is worthy of a Nobel Prize. This represents the start of a new age in black hole research.”
(This article was written by Tetsuya Ishikura and Ryoma Komiyama.)