It is widely believed that our Universe was born about 14 billion years ago with an infinite temperature and density, which is called the "Big Bang". As the Universe expanded and cooled down, various forms of matter were created, and the structures such as galaxies and stars emerged later. The main objective of our research group is to understand the various astrophysical processes that took place during the course of cosmic evolution, and clarify the formation and evolution of various astrophysical systems. We pursue a wide variety of research topics, including structure formation & cosmology, high energy astrophysics, jets, accretion disks, black holes, cosmic rays, galaxy clusters, dark matter, general relativity, gravitational wave astronomy, galaxy formation, star formation, proto-planetary disks, to name a few. In these topics, hydrodynamics, plasma physics and thermodynamics play important roles often case.
1) Structure Formation and Cosmology (large scale structure in the Universe, intergalactic medium, galaxy formation, clusters of galaxies, cosmic magnetic fields)
2) Formation of Astrophysical Bodies (planets, stars, galaxies, black holes)
3) Astrophysical plasma, magneto-hydrodynamics, solar physics
4) High Energy Emission from Astrophysical Objects
5) Gravitational Wave Astronomy

1)Observational study of optically thin hot plasma
2)Study of active galactic nuclei in X-ray observations
3)R&D of CCD cameras onboard X-ray satellites
4)Development of techniques of X-ray spectroscopy and X-ray polarimetry

Our universe is dominated by optically thin hot plasma. For example, X-ray emitting hot gas occupies a substantial fraction of the luminous matter in the clusters of galaxies, which is still much less than that of the dark matter. Therefore, the distribution of the hot gas in our universe is practically a key clue to investigate the universe. In our galaxy, the hot gas generated in the supernova explosion collides with the interstellar matter, producing high energy cosmic rays. In the vicinity of a blackhole, high temperature gas is also generated, forming jet phenomena.

We are performing observation of high temperature gas using detectors onboard various satellites. We have developed X-ray CCD cameras for the Space Station that was launched in July, 2009. . We are now developing CCD cameras for ASTRO-H. Finally, we are developing new techniques of spectroscopy and polarimetry for the future application.

(1) Spectrophotometric observation of X-ray radiation from dilute high-temperature plasma
Thermal radiation from dilute high-temperature plasma such as that surrounding supernova remnants or galaxy cluster contains numerous emission lines from heavy atoms. We are studying physical states of such plasma to determine its atomic composition and state through spectrophotometric observations. We are investigating the circulation of matter and energy in the universe to understand the evolution of the universe.

(2) Observation of active galaxies
Active galaxies are so bright that we can observe them despite of their far distance from the Earth. Observation of the large amount of produced energy and its temporal variation from the center of galaxies indicates the existence of giant black holes. In addition, the active galaxies are in such a far distance that the observation can also explore the time evolution of the early universe.

(3) Observation by using X-ray satellites and preparation of future generation of satellites
The Suzaku satellite was launched in July 2005. The XIS (CCD camera) has been functioning properly to observe various targets. In July, 2009, the SSC (CCD camera) onboard the MAXI was launched by the Space Shuttle. We are responsible for X-ray CCD cameras (XIS and SSC) for both satellites. The CCDs employed

(4) Research and development of new detector systems
Observation with superior detectors or techniques provides new findings. We are developing SD-CCD that can cover the energy range up to 100keV. By combining a super-mirror technology, we are planning to perform precise observation in hard X-ray region. We are also applying our technology in Earth observation satellite and in the laboratory experiments.

(5) Research and development of new detector systems
Observation with superior detectors or techniques provides new findings. We are developing such superior radiation detectors for the future satellite projects. We are applying our superior detector technology to observations with balloon-born experiments and small scientific satellites, as well as to ground experiments.

We study dynamics, statistics, and universality in nonequilibrium phenomena on the Earth and planets. Our approaches are theoretical, particularly statistical mechanics (either equilibrium and nonequilibrium), nonlinear dynamics, stochastic processes, and various computational methods.

1)Physics of friction, fracture, and earthquakes: Time series analyses and statistical aspects of fracture and its potential applicability for earthquake forecast. Mechanical models for fracture and earthquakes. Physics of friction across the scales.

2)Dynamics of nonequilibrium phenomena in earth and planetary sciences: Heat conduction, spin flux, granular flow, etc. Phenomena where fluxes, diffusion, and phase transitions are interrelated. Such phenomena are investigated from the viewpoint of nonequilibrium statistical mechanics.

3)Statistical physics of frustrated spin systems: Ordering and defects in pyrochlore and triangular lattices.

1)The origin and the formation of our solar system.
2)The evolution of the Earth and planets.
3)The magnetic properties of magnetic & weak magnetic planetary materials.
4)The studies on the laboratory/environmental electromagnetic phenomena.
5)Development of the technique/instrument for a new frontier of planetary science

As far as we know, the planet Earth is a unique environment (especially for life). When and how were the Earth and other planets formed in the entire universe?

To decipher the history of the Earth, we focus on the origin, evolution and current environment of our solar system based on various experimental approaches. Mainly, we carry out precise isotopic analyses from hydrogen to uranium in Apollo samples, Martian meteorites, other various meteorites and circum-stellar dusts. We also conduct the studies on the organic matter in planetary materials. For better understanding of the magnetic structure of the primordial solar nebula, the magnetic properties of magnetic & weak magnetic planetary materials are examined. We are also investigating electron spin resonance and the relation between environmental electromagnetic field and natural phenomena.

1)Phase transition and physical property change of minerals in the Earth's interior.
2)Origin and evolution of the Earth.
3)Phase transition in frustrated magnets under extreme conditions.
4)Development of technologies to produce extremely high pressure and high/low temperature, and perform measurements under such extreme conditions.

Our research interests are in the change of materials under extreme conditions of high pressure, high/low temperature, and strong magnetic field. Such conditions are generally realized in planetary interiors in nature. Most materials change their physical and chemical properties drastically in planets. For example, phase transition, crystal structure, density, elastic constants, electrical and magnetic properties, bonding nature, and chemical reaction with coexisting phases, are important clues for the geophysical modeling of planets. They affect the global structure, evolution and dynamics from the core to the surface. We generate extreme conditions in our laboratory by using various techniques of high-pressure generation (multi-anvil apparatus, laser-heated diamond anvil cell, laser shock), and then cook high-density materials and measure their property changes with various in-situ observation techniques of X-ray diffraction (synchrotron), imaging, spectroscopy, and electrical and magnetic measurements. Through these laboratory-based experiments, we strive for the comprehensive understanding of the planetary system and materials.

We study astronomical phenomena by infrared observations (including visible light and submillimeter wavelengths) using ground-based telescopes and space telescopes, and develop instruments for such observations. In particular, we focus on understanding the formation process of exoplanets and aim to detect extrasolar biosignatures in the future. We are also conducting research on optical and near-infrared identification of gravitational wave sources (black holes and/or neutron star mergers), galaxy structure, and dark matter.

1. MOA: More than 4,000 exoplanets have been discovered so far, but few of them are as small as the Earth outside the snow line, which is important for planet formation research. Therefore, we are using gravitational microlensing to search for such exoplanets. We are using MOA-II, a dedicated 1.8m wide-field telescope in New Zealand. We collaborate with Nagoya University, Auckland University, Massey University, Canterbury University, and NASA.

2. PRIME: A new wide-field telescope in the Republic of South Africa will be built to conduct microlensing planet survey in the near-infrared. The PRIME project is a collaboration with Astrobiology Center, Nagoya University, Massey University, SAAO, University of Maryland, JAXA, and NASA.

3. Roman: We participate in NASA's Roman mission scheduled for launch in 2025 to conduct microlensing planet survey from space. The goal is to reveal the distribution of all planets outside the Earth's orbit and to understand the process of planetary system formation. A joint research with JAXA, NAOJ, and NASA.

4. Searching for biosignatures: In preparation for NASA's proposed very large space telescope mission (OST, LUVOIR) in the 2030s, we are investigating and demonstrating technologies for the search for life outside the solar system. In collaboration with NASA, we are developing a highly stable instrument for use onboard satellites to measure the atmospheric composition of exoplanets and find traces of life (biosignatures) using direct imaging and transit spectroscopy method.

5. We study exoplanets, stars, and protoplanetary disks by using space and ground-based telescopes such as Kepler, TESS, Gaia, and ALMA. In particular, we aim to reveal the formation and evolutionary processes of various planetary systems through detailed studies of the orbital structures of transiting planetary systems.

The Earth, planets, the moon and satellites have wide varieties in surface environments and interior structures. Differentiation of materials along with planetary thermal evolution played a crucial role in the present state of these solar system bodies. Using spacecraft and ground observations, simulations, and experimental methods, we investigate the origin and evolution of various solar system bodies from dust particle to gas giant planets.

1)Formation and evolution processes of solid planets, satellites, and solar system small bodies, and their igneous processes.
2)Phase transitions and physical properties of the Earth's deep interior (Ultra-high pressure experiments using synchrotron radiation on the Earth's interior materials and their simulants).
3)Formation processes of the Earth's surface materials and topography (gas hydrates and igneous rocks).
4)Developments of new apparatus and techniques (e.g., microtomography using synchrotron radiation, three-dimensional image analysis, hyperspectoral telescope, etc.).
5)In situ detection of interplanetary and interstellar dust (e.g. BepiColombo mission) and development of dust accelerator.
6)Material sciences and instrument developments in space missions (e.g., HAYABUSA, KAGUYA, HAYABUSA-2, SELENE-2, JUICE).