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SIRIUS Project: Dynamical Evolution of Primordial Binaries during Star Cluster Formation
Naoto Harada, Michiko S. Fujii, Takayuki R. Saitoh +1
Binary populations are closely linked to the star formation process; however, their primordial properties can be changed by subsequent dynamical interactions within their natal clu…
SIRIUS: Dark matter cusp evolution in dense dwarf galaxies
Katsuhiro Kaneko, Takayuki R. Saitoh, Yutaka Hirai +1
Dwarf galaxies have a wide variety of structures, such as dark matter (DM) distribution, stellar-to-halo mass ratio, and stellar density. Recent high-resolution simulations have sh…
Nitrogen enhancement of GN-z11 by metal pollution from supermassive stars
Sho Ebihara, Michiko S. Fujii, Takayuki R. Saitoh +4
Spectroscopic observations by the James Webb Space Telescope (JWST) have revealed young, compact, high-redshift () galaxies with high nitrogen-to-oxygen (N/O) ratios. GN-z11 at…
Bursty star formation, chemical enrichment, and star cluster formation in numerical analogues of GN-z11
Takayuki R. Saitoh, Yutaka Hirai, Michiko S. Fujii +1
The James Webb Space Telescope reveals anomalous nitrogen enrichment (high N/O ratios) in compact, star-forming galaxies, such as GN-z11 at . The origin of this chemical s…
The First Star-by-star -body/Hydrodynamics Simulation of Our Galaxy Coupling with a Surrogate Model
Keiya Hirashima, Michiko S. Fujii, Takayuki R. Saitoh +9
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-sca…
SIRIUS: Identifying Metal-poor Stars Enriched by a Single Supernova in a Dwarf Galaxy Cosmological Zoom-in Simulation Resolving Individual Massive Stars
Yutaka Hirai, Takayuki R. Saitoh, Michiko S. Fujii +2
Metal-poor stars enriched by a single supernova (mono-enriched stars) are direct proof (and provide valuable probes) of supernova nucleosynthesis. Photometric and spectroscopic obs…
ASURA-FDPS-ML: Star-by-star Galaxy Simulations Accelerated by Surrogate Modeling for Supernova Feedback
Keiya Hirashima, Kana Moriwaki, Michiko S. Fujii +5
We introduce new high-resolution galaxy simulations accelerated by a surrogate model that reduces the computation cost by approximately 75 percent. Massive stars with a Zero Age Ma…
Gravitational Wave Astronomy With TianQin
En-Kun Li, Shuai Liu, Alejandro Torres-Orjuela +50
The opening of the gravitational wave window has significantly enhanced our capacity to explore the universe's most extreme and dynamic sector. In the mHz frequency range, a divers…
Simulations predict intermediate-mass black hole formation in globular clusters
Michiko S. Fujii, Long Wang, Ataru Tanikawa +2
Intermediate-mass black holes (IMBHs) are those between 100 and 10 solar masses (); their formation process is debated. One possible origin is the growth of less mas…
Surrogate Modeling for Computationally Expensive Simulations of Supernovae in High-Resolution Galaxy Simulations
Keiya Hirashima, Kana Moriwaki, Michiko S. Fujii +4
Some stars are known to explode at the end of their lives, called supernovae (SNe). The substantial amount of matter and energy that SNe release provides significant feedback to st…
Compact Binary Formation in Open Star Clusters I: High Formation Efficiency of Gaia BHs and Their Multiplicities
Ataru Tanikawa, Savannah Cary, Minori Shikauchi +2
Gaia BHs, black hole (BH) binaries discovered from database of an astrometric telescope Gaia, pose a question to the standard binary evolution model. We have assessed if Gaia BHs c…
3D-Spatiotemporal Forecasting the Expansion of Supernova Shells Using Deep Learning toward High-Resolution Galaxy Simulations
Keiya Hirashima, Kana Moriwaki, Michiko S. Fujii +3
Supernova (SN) plays an important role in galaxy formation and evolution. In high-resolution galaxy simulations using massively parallel computing, short integration timesteps for…
Gravitational wave of intermediate-mass black holes in Population III star clusters
Long Wang, Ataru Tanikawa, Michiko Fujii
Previous theoretical studies suggest that the Population III (Pop3) stars tend to form in extremely metal poor gas clouds with approximately embedded in mini dark ma…
SIRIUS Project. V. Formation of off-center ionized bubbles associated with Orion Nebula Cluster
Michiko S. Fujii, Kohei Hattori, Long Wang +4
Massive stars born in star clusters terminate star cluster formation by ionizing the surrounding gas. This process is considered to be prevalent in young star clusters containing m…
Impact of bar resonances in the velocity-space distribution of the solar neighbourhood stars in a self-consistent -body Galactic disc simulation
Tetsuro Asano, Michiko S. Fujii, Junichi Baba +3
The velocity-space distribution of the solar neighbourhood stars shows complex substructures. Most of the previous studies use static potentials to investigate their origins. Inste…
SIRIUS Project. IV. The formation history of the Orion Nebula Cluster driven by clump mergers
Michiko S. Fujii, Long Wang, Yutaka Hirai +3
The Orion Nebula Cluster (ONC) is an excellent example for understanding the formation of star clusters. Recent studies have shown that ONC has three distinct age populations and a…
SIRIUS Project. III. Star-by-star simulations of star cluster formation using a direct N-body integrator with stellar feedback
Michiko S. Fujii, Takayuki R. Saitoh, Yutaka Hirai +1
One of the computational challenges of cluster formation simulations is resolving individual stars and simulating massive clusters with masses of more than without…
SIRIUS project II: a new tree-direct hybrid code for smoothed particle hydrodynamics/N-body simulations of star clusters
M. S. Fujii, T. R. Saitoh, L. Wang +1
Star clusters form via clustering star formation inside molecular clouds. In order to understand the dynamical evolution of star clusters in their early phase, in which star cluste…
SIRIUS project. I. Star formation models for star-by-star simulations of star clusters and galaxy formation
Yutaka Hirai, Michiko S. Fujii, Takayuki R. Saitoh
Most stars are formed as star clusters in galaxies, which then disperse into galactic disks. Upcoming exascale supercomputational facilities will enable performing simulations of g…
The Keplerian three-body encounter II. Comparisons with isolated encounters and impact on gravitational wave merger timescales
Alessandro A. Trani, Mario Spera, Nathan W. C. Leigh +1
We investigate the role of the Keplerian tidal field generated by a supermassive black hole (SMBH) on the three-body dynamics of stellar mass black holes. We consider two scenarios…
Kinematics of Subclusters in Star Cluster Complexes: Imprint of their Parental Molecular Clouds
M. S. Fujii
Star cluster complexes such as the Carina Nebula can have formed in turbulent giant molecular clouds. We perform a series of -body simulations starting from subclustering initia…
Growth of intermediate mass black holes by tidal disruption events in the first star clusters
Yuya Sakurai, Naoki Yoshida, Michiko S. Fujii
We study the stellar dynamics of the first star clusters after intermediate-mass black holes (IMBHs) are formed via runaway stellar collisions. We use the outputs of cosmological s…
The Keplerian three-body encounter I. Insights on the origin of the S-stars and the G-objects in the Galactic center
Alessandro A. Trani, Michiko S. Fujii, Mario Spera
Recent spectroscopic analysis has set an upper limit to the age of the S-stars, the ~30 B-type stars in highly eccentric orbits around the supermassive black hole (SMBH) in the Gal…
Modeling the Milky Way as a Dry Galaxy
Michiko S. Fujii, Jeroen Bédorf, Junichi Baba +1
We construct a model for the Milky Way Galaxy composed of a stellar disc and bulge embedded in a dark-matter halo. All components are modelled as -body systems with up to 8 bill…