University of the Ryukyus · Faculty of Science · 教授

Research keywordsnumerical relativity・neutron star mergers・binary black holes・compact object initial data・magnetohydrodynamics・black hole horizon detection・gravitational waves

Research fieldsParticle/Nuclear/Cosmic ray/Astro physics・Mathematics and Physics・Physics・Science and Engineering

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• General-relativistic resistive-magnetohydrodynamics simulations of self-consistent magnetized rotating neutron stars2025 · Cheong P.C.K.
• General Relativistic Stability and Gravitational Wave Content of Rotating Triaxial Neutron Stars2024 · Triaxial neutron stars can be sources of continuous gravitational radiation detectable by ground-based interferometers. The amplitude of the emitted gravitational wave can be greatly affected by the state of the hydrodynamical fluid flow inside the neutron star. In this work, we examine the most triaxial models along two sequences of constant rest mass, confirming their dynamical stability. We also study the response of a triaxial figure of quasiequilibrium under a variety of perturbations that lead to different fluid flows. Starting from the general relativistic compressible analog of the Newtonian Jacobi ellipsoid, we perform simulations of Dedekind-type flows. We find that in some cases the triaxial neutron star resembles a Riemann-S-type ellipsoid with minor rotation and gravitational wave emission as it evolves towards axisymmetry. The present results highlight the importance of understanding the fluid flow in the interior of a neutron star in terms of its gravitational wave content.
• The Parallel Compact Object CALculator: An Efficient General Relativistic Initial Data Solver for Compact Objects2024 · Boukas, L; Tsokaros, A; Uryu, K
• The Parallel Compact Object CALculator: An Efficient General Relativistic Initial Data Solver for Compact Objects2024 · Every numerical general relativistic investigation starts from the solution of the initial value equations at a given time. Astrophysically relevant initial values for different systems lead to distinct sets of equations that obey specific assumptions tied to the particular problem. Therefore, a robust and efficient solver for a variety of strongly gravitating sources is needed. In this work, we present the OpenMP version of the Compact Object CALculator (COCAL) on shared memory processors. We performed extensive profiling of the core COCAL modules in order to identify bottlenecks in efficiency, which we addressed. Using modest resources, the new parallel code achieves speedups of approximately one order of magnitude relative to the original serial COCAL code, which is crucial for parameter studies of computationally expensive systems such as magnetized neutron stars, as well as its further development towards more realistic scenarios. As a novel example of our new code, we compute a binary quark system where each companion has a dimensionless spin of 0.43 aligned with the orbital angular momentum.

• 定常波を伴う数値相対論の初期データ2022 · 基盤研究(C)
• 磁場をもつ連星中性子星の準平衡状態と数値相対論の初期データ
• 数値相対論的シミュレーションの多様な初期データの構築
• クォーク力学・原子核構造に基づく爆発的天体現象と元素合成

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