University	  of	  Tsukuba	  	  | Center	  for	  Computational	  Sciences

Solving	  the	  Mysteries	  of	  the	  Universe	  with	  Computational	  Astrophysics
GPU-­‐accelerated high-­‐fidelity gravity and	  radiation calculations
In the universe, gravity and radiation drive and regulate the formation of astrophysical objects such as galaxies, stars,planets, and black holes. The large dynamical range in density and thus gravitational force, and the short timescales involvedin the propagation and interaction of radiation with interstellar matter pose great challenges for computational astrophysics.
GPUs can provide substantial acceleration in N-­‐body and radiative transfer calculations.

We developed an extremely efficient GPU-­‐accelerated N-­‐bodycode, named GOTHIC. The code brings together many of themost effective schemes including the tree method and block
timestep (cf. shared timestep), and couples these with on-­‐the-­‐fly auto-­‐tuning to minimize execution time. The code
optimization and tests were done on Fermi, Kepler, andMaxwell generation GPUs with particle distributions
representing the Andromeda galaxy using 8M particles. The
calculations are faster than other leading codes, e.g. Bonsai,and exhibit accelerations up to 30% of the theoretical peakGPU performance in single precision.

We developed a new GPU-­‐accelerated code, which iscapable of accurately computing the propagation ofdiffuse recombination photons in three dimensions.
Diffuse photons affect the advance of ionization fronts
and alter the ionization state in shadow regions. Thiseffect can change the conditions of the interstellar
medium and star-­‐formation in the early universe.

Simulating	  protoplanetary disks and exploring the	  formation of	  planetary systems
Protoplanetary disks are rotating gas disks surrounding newly formed stars and contain micron-­‐sized dust particles, coveredby ice mantles. The dust particles coagulate to kilometer-­‐sized planetesimals, which grow by mutual collisions andeventually turn into planets. The surface environments of planets are thought to be largely determined by gas and icy
planetesimal accretion. Thus, the study of gas and ice chemical compositions in protoplanetary disks is important forunderstanding the beginning of life on planets.

Using the N-­‐body simulations including the effects of inelastic
collision and self-­‐gravity, we investigated the dynamics of dust
aggregates and the formation processes of planetesimals fromdust aggregates in a protoplanetary disk. When a dust layer
becomes sufficiently thin, the gravitational instability takes
place and dense dust regions form. The dense dust regions
facilitate dust growth and planetesimals form rapidly.

contact	  address:	  pr@ccs.tsukuba.ac.jp

We simulated the distribution of water vapor in a
protoplanetary disk around a typical T Tauri star. Various
physical and chemical processes, e.g., gas-­‐phasechemistry, grain surface chemistry, and chemistry inducedby stellar ultraviolet photons and X-­‐rays, are included. The
simulations reveal where and how much water is present
in the disk, and are useful for interpreting astrophysicalobservations of water in protoplanetary disks.
http://www.ccs.tsukuba.ac.jp/