Kawazura Yohei, Kimura Shigeo S
Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, 6-3 Aoba, Aramaki, Sendai 980-8578, Japan.
Department of Geophysics, Graduate School of Science, Tohoku University, 6-3 Aoba, Aramaki, Sendai 980-8578, Japan.
Sci Adv. 2024 Aug 30;10(35):eadp4965. doi: 10.1126/sciadv.adp4965. Epub 2024 Aug 28.
Accretion disks around compact stars are formed due to turbulence driven by magnetorotational instability. Despite over 30 years of numerous computational studies on magnetorotational turbulence, the properties of fluctuations in the inertial range-where cross-scale energy transfer dominates over energy injection-have remained elusive, primarily due to insufficient numerical resolution. Here, we report the highest-resolution simulation of magnetorotational turbulence ever conducted. Our simulations reveal a constant cross-scale energy flux, a hallmark of the inertial range. We found that as the cascade proceeds to smaller scales in the inertial range, the kinetic and magnetic energies tend toward equipartitioning with the same spectral slope, and slow magnetosonic fluctuations dominate over Alfvénic fluctuations, having twice the energy. These findings align remarkably with the theoretical expectations from the reduced magnetohydrodynamic model, which assumes a near-azimuthal mean magnetic field. Our results provide important implications for interpreting the radio observations by the Event Horizon Telescope.
致密恒星周围的吸积盘是由磁旋转不稳定性驱动的湍流形成的。尽管对磁旋转湍流进行了30多年的大量计算研究，但在惯性范围内波动的特性——其中跨尺度能量传递比能量注入占主导地位——仍然难以捉摸，主要是由于数值分辨率不足。在这里，我们报告了有史以来进行的最高分辨率磁旋转湍流模拟。我们的模拟揭示了一个恒定的跨尺度能量通量，这是惯性范围的一个标志。我们发现，随着级联在惯性范围内向更小尺度发展，动能和磁能趋向于以相同的谱斜率达到均分，并且慢磁声波波动比阿尔文波动占主导，能量是阿尔文波动的两倍。这些发现与简化磁流体动力学模型的理论预期非常吻合，该模型假设了一个近方位平均磁场。我们的结果对于解释事件视界望远镜的射电观测具有重要意义。
