The First Star-by-star N-body/Hydrodynamics Simulation of Our Galaxy Coupling with a Surrogate Model

Keiya Hirashima, Michiko S. Fujii, Takayuki R. Saitoh, Naoto Harada, Kentaro Nomura +7 more
10/27/2025
astro-ph.GAcs.DCcs.LG

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Abstract

A major goal of computational astrophysics is to simulate the Milky Way Galaxy with sufficient resolution down to individual stars. However, the scaling fails due to some small-scale, short-timescale phenomena, such as supernova explosions. We have developed a novel integration scheme of $N$-body/hydrodynamics simulations working with machine learning. This approach bypasses the short timesteps caused by supernova explosions using a surrogate model, thereby improving scalability. With this method, we reached 300 billion particles using 148,900 nodes, equivalent to 7,147,200 CPU cores, breaking through the billion-particle barrier currently faced by state-of-the-art simulations. This resolution allows us to perform the first star-by-star galaxy simulation, which resolves individual stars in the Milky Way Galaxy. The performance scales over $10^4$ CPU cores, an upper limit in the current state-of-the-art simulations using both A64FX and X86-64 processors and NVIDIA CUDA GPUs.

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Cite this paper

@article{hirashima2025first,
  title  = {The First Star-by-star N-body/Hydrodynamics Simulation of Our Galaxy Coupling with a Surrogate Model},
  author = {Keiya Hirashima and Michiko S. Fujii and Takayuki R. Saitoh and Naoto Harada and Kentaro Nomura and Kohji Yoshikawa and Yutaka Hirai and Tetsuro Asano and Kana Moriwaki and Masaki Iwasawa and Takashi Okamoto and Junichiro Makino},
  year   = {2025},
  eprint = {2510.23330},
  archivePrefix = {arXiv},
  url    = {http://arxiv.org/abs/2510.23330v1}
}

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