University of Tsukuba | Center for Computational Sciences

Division of Astrophysics

Chief: Ohsuga Ken, Professor, Ph.D.

We apply fundamental physics to investigate a wide variety of astrophysical phenomena, including the birth and evolution of the firststars and galaxies in the universe, the characteristics of the light they emit, the formation and evolution of galaxies, galaxy clusters, andother large-scale structures, the formation and evolution of black holes and their jets and radiation, the formation of planets, and the originof life in the universe. We are also researching how technology developed in this field may find applications in medicine.

Black-hole physics

Fig.1
Left: Black hole accretion disks and jets in generalrelativistic radiative magnetohydrodynamic simulations.
Right: Black hole shadow reproduced by general relativistic
radiative transfer calculations

In the accretion disk, where matter accumulates owing to the strong gravity ofthe black hole, powerful radiation and jets are generated through the release ofgravitational energy. We are investigating high-energy astrophysical phenomena
around black holes and the radiation from black-hole phenomena throughgeneral-relativistic radiation-magnetohydrodynamic simulations.

Supermassive black holes and galaxy evolution
Every galaxy harbors a supermassive black hole at its center that grows by swallowing stars andinterstellar matter and simultaneously launches powerful jets into the galaxy that blow away interstellar
gas and regulates star formation and black hole growth. We are investigating these complex cycles ingalaxy evolution through relativistic magnetohydrodynamic simulations.
Fig. 3 Interaction between interstellar gas and jets

Star cluster formation
Most stars are born as members of star clusters in the Universe. The physical processes instar-cluster formation determine the properties of the stars. We are studying star-cluster
formation and cloud dispersal by radiative feedback using radiation hydrodynamics simulations.
Fig. 2 Cloud dispersal by radiative feedback in star cluster formation

Galaxy evolution and dark matter

Galaxy formation

Dark matter is known to play animportant role in the evolution ofgalaxies, but its nature remains
shrouded in mystery, and manyIn the early universe, massive galaxies and supermassive black
holes may have formed through frequent merging of galaxies andrapid gas accretion in primordial galaxyclusters. We are studying physicalcontradictions within existing theories phenomena occurring in primordialpersist. We are investigating the nature galaxy clusters through cosmologicalradiation-hydrodynamic simulations.
of dark matter haloes by studying
Fig. 4 A galaxy collision thatFig.5 Upper left: Large-scale matter distribution in the universe.
occurred in the Andromeda Galaxy galaxy collisions.
approximately 1 billion years ago

Upper right: Structure of gas near the central galaxy in a proto-galaxy cluster.
Bottom: From left to right, galactic gas, heavy elements, and stellar surface density.

Neutrinos and the formation of large-scale structures in the universe
We have conducted the world’ s first high-precision Vlasov simulations of the large-scalestructure in the universe that include neutrinos and that outperform conventional N-bodysimulation. The simulations can be used in conjunction with future observational projects oflarge-scale galaxy survey to constrain the neutrino mass.
Fig. 6 Left: Large-scale structure with neutrinos.
Right: Large-scale structure without neutrinos.

Applications of astrophysical techniques in medicine
Diffuse optical tomography (DOT) using near-infrared light in the wavelength range of 700-1000 nm has
been garnering attention as a new medical diagnostic method because it is non-invasive and does not
expose the patient to radiation. We are studying light propagation in living organisms by applying
high-precision techniques for radiative transfer calculation developed in astrophysics to DOT.

Fig. 7 Radiative transfer in live
tissue irradiated by pulsed lighthttps://www.ccs.tsukuba.ac.jp/