Shigeru Yoshida,
Director,
International Center for
Hadron Astrophysics,
Chiba University

Throughout history, humankind has looked up to the stars in wonder, marveling at the mysteries of the universe, but the part that we can see with our own eyes is only a mere sliver of what lies out there. The signals that we pick up from the universe are observed not only in visible light; they span the entire electromagnetic spectrum, from radio waves to infrared, from x-rays to gamma rays, from waves hundreds of thousands of meters in length to waves as small as a picometer. Observing each of those different radiation bands has given us a new window for looking out into the universe and has shown us things that we could never have imagined.

However, electromagnetic radiation is not the only thing we can see in the universe. We have discovered that our planet is being constantly bombarded by mysterious particles called “neutrinos,” elementary particles with energy one quadrillion times or 1015 times higher than that of visible light. Neutrinos are able to pass through almost all forms of matter, which means when they arrive at our planet their properties are the same as they were when emitted, even if they came from the far end of the universe. Neutrinos are subatomic particles related to the electrons with which we are all familiar, but unlike electrons, neutrinos hold no charge, and they travel at almost the speed of light. Neutrinos, mysterious particles carrying orders of magnitude more energy than other particles, are made somewhere out there in the universe. But what does this mean?

All matter in the universe contains the subatomic particles called protons, and it is known that subatomic particles are blown up to ultimate energies and emitted as super energetic radiation. (By the way, protons are a type of subatomic particle called a hadron, which is where part of the name of our center comes from.) We learned about this property of subatomic particles by observing and understanding the radiation we call cosmic rays. However, no one knew where they came from. Somewhere out there in the universe, something was accelerating protons and atomic nuclei to extremely high energies. Somewhere, there are astronomical bodies acting as engines, operating through some unknown mechanism. However, those great astronomical engines remain hidden because magnetic fields and other forms of radiation interfere with the cosmic rays between the time the rays leave their sources and the time they arrive at Earth. This is where the neutrinos come into play.

Neutrinos can pass through all forms of matter, so after they are emitted, they can travel unmolested through the universe until they arrive at Earth. They can provide a direct statement about their point of origin. Scientists recognized the potential there, and a large-scale observatory called IceCube was built at the South Pole in order to observe neutrinos. This allowed us to confirm that neutrinos were really being generated throughout the universe, and in numbers consistent with theoretical projections. We were even able to identify a unique galaxy located four billion light years away as being a source of neutrinos. That was the moment the field of high-energy neutrino astronomy was born.

Chiba University’s International Center for Hadron Astrophysics (ICEHAP) is the leading high-energy neutrino astronomy research institution not only in Japan, but throughout Asia and Oceania as well. As a part of the IceCube Collaboration, which is comprised of member institutions from 12 different countries, ICEHAP made the leading contributions to the world’s first discovery of high-energy cosmic neutrinos in 2012, and led the effort to the first identification of a neutrino-emitting object in 2017. We are playing an important role in the remarkable progress being made in the field of Neutrino Astronomy. We are currently preparing to engage in observational experiments of even greater scale in order to discover more neutrino emitters and to unravel the true nature of how they generate neutrinos.

To understand that mechanism, we must also harness supercomputers to conduct numerical simulations in addition to observations. The issue lies in the fact that we cannot simply take an astronomical body and placed it within the controlled environment of a research laboratory. At ICEHAP, we have a top-class research team that uses the supercomputer Fugaku, the pride of Japan, to conduct simulations of plasma dynamics around neutrino sources and simulations of proton and electron radiation associated with those phenomena. ICEHAP’s mission is to unravel the mysteries behind the universe’s extreme energy sources, through observational neutrino research and through conducting numerical simulations that make use of computer technologies.

Welcome to the cutting-edge of astronomy research: the International Center for Hadron Astrophysics, ICEHAP.

Shigeru Yoshida,
Director,
International Center for Hadron Astrophysics,
Chiba University