Research Overview

Cool Observations of a Hot Universe!

X-rays originate from extremely "hot" regions, with temperatures exceeding ten million degrees, or from high-speed particles traveling close to the speed of light. We now know that X-rays are emitted from all cosmic scales — from planets and comets to galaxy clusters. In other words, most celestial objects exhibit some form of high-energy activity. Our aim is to observe X-rays arriving from space, analyze the data while considering physics, and unravel the mysteries of high-energy phenomena in the universe — with a cool, scientific approach.

Research in High-Energy Astrophysics

Our laboratory studies a variety of celestial objects such as black holes, neutron stars, magnetars, as well as supernova remnants and explosive stellar phenomena that follow stellar deaths mainly based on X-ray observations. In particular, compact objects provide natural laboratories for studying extreme environments — such as strong gravitational and magnetic fields — that cannot be replicated on Earth. Understanding the origin and evolution of these objects also leads to a better grasp of large-scale cosmic structures like galaxies. Now, the cutting-edge X-ray satellite XRISM provides crucial data for revealing the dynamics of structures around compact objects, including accretion disks and relativistic plasma outflows. In addition to data analysis, quantitative comparison with theoretical models is essential for research progress. To that end, we have developed our own Monte Carlo radiation transport simulation code to model X-ray emission processes under diverse physical conditions, aiming to interpret the observations theoretically.

Keywords

Next-Generation Space Missions and Instrumentation

Another pillar of our research is the development of observational instruments for X-ray astronomy. Our laboratory was a core contributor to the development of the X-ray CCD camera onboard XRISM, launched in September 2023. This CCD operates at -110 to -120 degrees in orbit to reduce noise and can capture wide-field X-ray images and spectra — covering a field of view larger than a full moon. XRISM is also equipped with an X-ray microcalorimeter, cooled to an ultra-low temperature of 50 mK, enabling ultra-high-resolution X-ray spectroscopy. In this way, XRISM observes the hot universe with "cold eyes". We are also developing a new type of detector — a liquid argon time projection chamber — to pioneer MeV gamma-ray astronomy and explore the nature of dark matter. This detector also operates at a "cold" -185 degrees. Additionally, we are engaged in the international balloon-borne experiment XL-Calibur, a collaboration between Japan, the U.S., and Sweden. In this project, a balloon is launched from Antarctica — an extremely cold region — to observe the polarization of hard X-rays during long-duration flights. We are also working on technologies for the realization of future high-performance X-ray telescopes.

Keywords