Ultra-high-resolution magnetohydrodynamic simulations for the small-scale properties of accretion disk turbulence

2023 Fiscal Year Final Research Report

• Project/Area Number: 20K14509
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 16010:Astronomy-related
• Research Institution: Tohoku University
• Principal Investigator: Kawazura Yohei 東北大学, 学際科学フロンティア研究所, 助教 (80725375)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Keywords: 降着円盤 / プラズマ乱流 / 電磁流体力学 / 並列計算

Outline of Final Research Achievements

In this study, we developed a pseudospectral code to accurately solve the local turbulence in accretion disks and succeeded in performing the highest-resolution magnetorotational turbulence simulation ever using the Fugaku supercomputer. As a result, while it has been known that magnetic energy exceeds kinetic energy in previous magnetorotational turbulence studies, we discovered that at smaller scales, magnetic energy and kinetic energy are energetically equipartitioned, leading to an 'Alfven turbulence state' where the spectrum follows a -3/2 power law of the wavenumber. Additionally, we found that the energy of slow magnetosonic waves is twice that of Alfven waves. These results perfectly match our previous predictions derived from a reduced magnetohydrodynamic model.

Free Research Field

プラズマ物理、天体物理学

Academic Significance and Societal Importance of the Research Achievements

降着円盤における乱流の特性は３０年以上の未解決問題であった。本研究は、富岳を用いた超高解像度シミュレーションによってその答えを世界で初めて導いたという点において学術的な意味が大きい。また、その結果が簡約化磁気流体モデルの予測と一致するため、今後は降着円盤の微小スケールに関する研究は、高解像度シミュレーションを使わなくても、簡約化電磁流体で僅かな数値資源のシミュレーションで十分であるということを意味しており、数値計算に必要な環境負荷の低減につながるだろう。