Yasuo Tanaka (1932–2018)

Reprinted with permission from Joachim Trümper

Yasuo Tanaka died of a heart attack in Tokyo on January 18, 2018, just three months after returning from a 23-year stay at the Max Planck Institute for Extraterrestrial Physics (MPE) in his homeland. At MPE he completed most of his rich life's work in the field of high-energy astrophysics and promoted scientific exchange between Japan and Germany / Europe. He leaves his wife Toshiko and three sons with their families.

Yasuo Tanaka was born in 1931 near Osaka, Japan, as the middle of three sons. During the Second World War, he had to work as a child in a factory and endure heavy bombing, but in the following years he also suffered distress and hunger. He joined the Physics Department of Osaka University in 1950 and earned his doctorate in physics in 1961, when he was also a member of a working group led by Minoru Oda on the air shower experiment at the Institute for Nuclear Study (University of Tokyo).

We met for the first time in August 1961 at the Cosmic Ray Conference in Kyoto; Afterwards he showed me the very impressive air show in Tokyo. In 1962 he accepted an offer from Satio Hayakawa to become assistant professor at Nagoya University, and just one year later he accepted an invitation from Jan Oort to come to the Netherlands. It was his first contact with the western astronomy community, and later he often said that those four years had changed his life. Conversations with the famous astrophysicists Jan Oort and Henk van de Hulst opened up new horizons for the young scientist, and Lo Woltjer and Johann Bleeker, almost the same age, became his lifelong friends. Together with Bleeker he launched the Nagoya Leiden collaboration, which had the goal

At the same time, in 1962, Riccardo Giacconi and his group discovered the first extrasolar X-ray source Sco X-1 and soft X-ray background radiation, altering the lives of many scientists who had previously studied cosmic rays. This also applied to Tanaka and Bleeker, who shifted the focus of their joint balloon program of electrons to the hard X-ray background. This pioneering work was continued after Tanaka returned to Nagoya in 1967, where he participated in the X-ray satellite program initiated by his teacher Oda at the University of Tokyo.

In 1974, Tanaka joined the Institute of Space and Aeronautical Engineering (ISAS), which had become the center for space research in Japan. During his 20 years at ISAS he designed the research program in X-ray astronomy. He was Principal Investigator for four X-ray satellites: Hakucho (started in 1979), Tenma (1983), Ginga (1987) and ASCA (1993). For two more missions that were observations of the Sun, Hinotori (1981) and Yohkoh he was a consultant.

This impressive series of X-ray satellites has led to a long list of important scientific findings and discoveries in various fields of astrophysics. Tanaka's own interest was primarily to observe matter-accreting stellar and massive black holes. He co-authored a series of reviews on the subject and was the lead author of a groundbreaking article in the journal Naturewhich was based on the discovery of the broad and unsymmetrical iron Ka line in the spectrum of the active galaxy MCG-6-30-15 with ginga, and opened up a completely new diagnosis of the accretion disk near the black hole. Also, the following mission ASCA was a great success. ROSAT and ASCA, which complemented each other perfectly with their complementary properties, dominated X-ray astronomy in the 1990s. Tanaka's great achievements at ISAS were the result of his organizational skills, coupled with foresight and determination.

After retiring from ISAS in 1994, Tanaka accepted an invitation to the MPE, which was funded by a Humboldt Prize. During his 23 years at the MPE, he continued his scientific research together with scientists from the MPE, the MPA and his former colleagues in Japan. In 1995, he was appointed Director of the European-German Office of the Japanese Society for the Advancement of Science (JSPS) in Bonn, whose work he largely directed from 1995 to 2008 from the MPE.

Tanaka has received numerous awards from national and international organizations for his achievements. In Germany, he was awarded the Humboldt Prize (1994), the Eugen and Ilse Seibold Prize of the Deutsche Forschungsgemeinschaft (1999) and the Order of Merit of North Rhine-Westphalia. In 2001, he was appointed External Scientific Member of the MPE. The last and most important recognition for him was the election to the prestigious Japan Academy 2012.

Until recently, Tanaka participated actively in scientific life at MPE and MPA. Every morning he came to the institute and stayed until late in the evening. At our daily lunches, we enjoyed talking about the latest advances in astrophysics and world politics. Close friendships with many joint meetings developed between the couple Tanaka and the married couples of some MPE and MPA colleagues. Yasuo Tanaka and his wife Toshiko loved the nearby mountains and lakes; During the holidays they traveled throughout Germany and on weekends through Bavaria. They enjoyed the rich cultural scene in Munich and often spent the New Year in Vienna, impressing in particular the "bat" by Johann Strauss.

In recent years, Tanaka's health has deteriorated significantly and he finally decided after a long struggle to return to Japan. In early October 2017, they flew home to their home in Tokyo and to their sons.

With Yasuo Tanaka, our institute and the astrophysical community are losing a great scientist and a friend with a warm and generous personality. He will be remembered best by his colleagues, friends and astronomers around the world.