International research groups such as Kyoto University have announced that they have actually discovered a new type of “supernova explosion” that a large-mass star causes at the end of its life, which has been theoretically considered. Called an “electron-captured supernova,” it was an important achievement in understanding the physics of the life of a star and the sudden phenomena that occur in the universe.
Stars continue to support their weight through internal fusion reactions. In the end, a star with a small mass becomes a “white dwarf” and supports its own weight without a nuclear reaction, while a star with a large mass cannot support its own weight and collapses, causing a supernova explosion. The mass of the star, which is the junction of these two phenomena, is said to be eight times that of the Sun.
In theoretical studies so far, it has been thought that the core of a star with the mass of a branch point is made of oxygen, neon, and magnesium. The core is supported by the pressure generated by the electrons, but at the end, the electrons are captured by magnesium and neon, and the core collapses and explodes.
An electron-capture type supernova with such a mechanism has been predicted by Kenichi Nomoto, a senior scientific researcher at the Kavli Institute for the Physics and Mathematics of the Universe, the University of Tokyo, for about 40 years, but has not been observed. There is a view that the 1054 supernova that Fujiwara no Teika wrote in his diary “Meigetsuki” was this type, but it is not clear.
Under these circumstances, in March 2018, an amateur astronomer from Yamagata Prefecture, Koichi Itagaki, discovered the supernova “2018zd” immediately after the explosion in the direction of Camelopardalis. Chiba Prefecture’s amateur astronomer, Toshihide Noguchi, recorded changes in brightness. In response to this, Daichi Hiramatsu, a graduate student at the University of California, Santa Barbara, formed an observation team and made detailed observations with telescopes and space telescopes around the world.
As a result of the analysis, the number of elements of the supernova, the explosive energy, and the environment around the star is in good agreement with the characteristics of the electron-capturing supernova predicted by theory and simulation. It was also found that the Hubble Space Telescope accidentally captured the supernova before the explosion and had eight times the mass of the Sun. From this, the research group concluded that 2018zd is an electron-capturing supernova.
Keiichi Maeda (Astrophysics), Associate Professor of the Graduate School of Science, Kyoto University, said, “This discovery is an important achievement that approaches the mystery of the turning point of whether a star will become a white dwarf or a supernova at the end. This type If we continue to discover and know the frequency of occurrence of these supernovae, we will know the turning point accurately. It is also important to understand the role of this type of supernovae in the synthesis of elements in the universe. ”
After a supernova explosion, relatively large stars collapse into black holes and small stars become dense “neutron stars”. In order to understand these origins, it is important to understand electron-captured supernovae. Associate Professor Maeda said, “This time, even in the present age when large-scale telescopes are active, we have shown once again that amateur astronomers have a great influence on astronomy.”
The research group consists of the University of California, Santa Barbara, Kyoto University, the University of Tokyo, and the National Astronomical Observatory. The results were published in the English astronomy magazine “Nature Astronomy” dated June 28th.