1987 →

Disclaimer: machine translated by DeepL which may contain errors.

Toshikazu Shigeyama, Professor, Research Center for the Early Universe (RESCEU)

One of my favorite Japanese rock bands, Spitz, wrote a song titled "1987. 1987 is the year when Spitz started their activities, and it is also the year that changed my life, hence the title of this essay. In late February of that year, I was a first-year graduate student in the Doctoral dissertation program, struggling to write my thesis for publication in the graduate student room of the Space and Earth Science Department in Komaba's Building No. 4. At that time, my advisor, Kenichi Nomoto (now a Visiting Senior Scientist at Kavli IPMU, The University of Tokyo), came to my room and said, "A supernova has appeared in the Large Magellanic Cloud. Will you stop your current research and help us model this supernova?" I remember that he said something to me to the effect of, "I want you to stop your current research and help me make a model of this supernova. The Large Magellanic Cloud is a small nearby galaxy, and this was the first time a supernova had appeared so close to a planet since Galileo Galilei observed it with his telescope. Prior to that, nearby supernovae had only been seen with the naked eye. Immediately after hearing this story, I immediately said "I'll do it" (I think).

Dr. Nomoto was one of the few researchers who could construct a model of how a massive star changes over time until just before it explodes into a supernova. Being in such a laboratory, there was no way for me to pass up this opportunity. The goal of my research was to build a numerical model of stellar explosions and compare the observed changes in color and brightness of supernovae with the model to determine what kind of star exploded and at what energy. Model building (≈program writing and bug catching) was a daily competition with new observation results. The frequency of sorting out problems and thinking about what to do next increased beyond comparison. It also became a habit to create a quantitative picture in my mind of the important physical processes taking place based on the calculation results. I felt like my brain had transitioned to an excited state.

The right image was taken on February 5, 1984, and the left image was taken on March 8, 1987, in the same region of the Large Magellanic Cloud. The arrow in the right image shows the exploded star at the end of the arrow. The image on the left shows a supernova in its brightening phase.Credit: David Malin © Australian Astronomical Observatory

From the beginning, there were rumors that neutrinos should have been received by Kamiokande II (the predecessor to the now operational Super-Kamiokande). However, the Koshiba Lab, which operates the Kamiokande II, was (apparently) kept in the dark. I remember that I was eagerly awaiting the detection report, because I thought that they would not do such a thing if they had not received the prize. As it turned out, 11 neutrinos were detected for about 13 seconds, about 3 hours before the discovery in visible light (as you all know, Masatoshi Koshiba, who led Kamiokande, was awarded the Nobel Prize in Physics 15 years later). From the energy and duration of the explosion, it was inferred that the central core of the exploded star, which has a mass about 1.5 times that of the Sun, underwent gravitational collapse. Our model, which reproduces the time difference between the neutrino detection and the supernova discovery, indicates that the exploded star was a blue supergiant with a relatively small radius. This is consistent with the star that disappeared when we compared pre- and post-explosion photographs of the region (Figure). The same model also revealed that this supernova was the explosion of a massive star with a mass about 15 times that of the Sun. These studies marked the beginning of a new type of astronomy, recently called multi-messenger astronomy, in which information from neutrinos and gravitational waves is added to electromagnetic waves. I also discovered the joy of learning various things from natural phenomena. Just as Spitz put their desire to continue their band's activities into their song, I would like to continue my exciting research as long as my brain remains in the excited state it has been in since that time.

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