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Magnetorotational dynamo chimeras - The missing link to turbulent accretion disk dynamo models?

机译：磁力电动发电机嵌入式 - 湍流增值磁盘发电机模型的缺失链接？

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In Keplerian accretion disks, turbulence and magnetic fields may be jointly excited through a subcritical dynamo mechanisminvolving magnetorotational instability (MRI). This dynamo may notably contribute to explaining the time-variability of various accreting systems, as high-resolution simulations of MRI dynamo turbulence exhibit statistical self-organization into large-scale cyclic dynamics. However, understanding the physics underlying these statistical states and assessing their exact astrophysical relevance is theoretically challenging. The study of simple periodic nonlinear MRI dynamo solutions has recently proven useful in this respect, and has highlighted the role of turbulent magnetic diffusion in the seeming impossibility of a dynamo at low magnetic Prandtl number (Pm), a common regime in disks. Arguably though, these simple laminar structures may not be fully representative of the complex, statistically self-organized states expected in astrophysical regimes. Here, we aim at closing this seeming discrepancy by reporting the numerical discovery of exactly periodic, yet semi-statistical “chimeral MRI dynamo states” which are the organized outcome of a succession of MRI-unstable, non-axisymmetric dynamical stages of different forms and amplitudes. Interestingly, these states, while reminiscent of the statistical complexity of turbulent simulations, involve the same physical principles as simpler laminar cycles, and their analysis further confirms the theory that subcritical turbulent magnetic diffusion impedes the sustainment of an MRI dynamo at low Pm. Overall, chimera dynamo cycles therefore offer an unprecedented dual physical and statistical perspective on dynamos in rotating shear flows, which may prove useful in devising more accurate, yet intuitive mean-field models of time-dependent turbulent disk dynamos.
机译：在拍摄型吸收磁盘中，湍流和磁场可以通过亚临界发电机机制透过磁化机构不稳定性（MRI）共同激发。该发电机可能尤其有助于解释各种增压系统的时间可变性，因为MRI发电机湍流的高分辨率模拟表现出统计自组织成为大规模的循环动态。然而，了解这些统计态的基础和评估其确切的天体物理相关性的物理学是理论上的挑战性。简单的周期性非线性MRI发电机解决方案的研究最近证明了在这方面有用，并且突出了湍流磁散扩散在低磁性PRANDTL号码（PM）的似乎不可能性中的作用，磁盘中的共同制度。但是，尽管如此，这些简单的层状结构可能不完全代表在天体物理制度中预期的复杂的统计上自组织状态。在这里，我们的目的是通过报告恰好周期性，半统计“ChimerAlar MRI发电机状态”的数值发现，这似乎是差异，这是一种不同形式的MRI-不稳定，非轴对称动态阶段的组织结果。幅度。有趣的是，这些状态，同时让人想起湍流模拟的统计复杂性，涉及与更简单的层循环相同的物理原理，并且它们的分析进一步证实了亚临界湍流磁散阻碍了在低PM下MRI发电机的维持的理论。总的来说，嵌合型发电机周期为旋转剪切流动的发电机提供了前所未有的双重物理和统计透视，这可能证明在设计更准确的湍流磁盘发电机的更准确，但直观的平均场模型方面可以证明。

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