Magneto-thermal instability in galaxy clusters - I. Theory and two-dimensional simulations
Magneto-thermal instability in galaxy clusters - I. Theory and two-dimensional simulations
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星系团中的磁热不稳定性——I.理论和二维模拟
DOI：
10.1093/mnras/stac974
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发表时间：
2022
影响因子：
4.8
通讯作者：
Perrone L
中科院分区：
文献类型：
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作者：
Perrone L
确定星系团中湍流的起源，并量化其热量传输，是一个突出的问题，对我们理解其热力学历史和结构具有重要意义。当团内介质（ICM）的稀等离子体被磁化时，热量和动量优先沿着磁场线传播。这种各向异性触发了一类浮力不稳定性，使ICM不稳定，其湍流运动可以增加或阻碍热传输。我们关注的磁热不稳定性（MTI），这可能是活跃在星系团的外围。我们的目标是重新审视这个问题，并构建一个通用的理论，解释MTI饱和机制，并提供缩放和估计的湍流动能，磁能和热通量。我们模拟MTI湍流与Boussinesq代码，史努比，这与以前的工作相比，使我们能够执行广泛的采样的参数空间。在两个维度的饱和机制涉及一个逆级联，携带动能从短MTI注入尺度到更大的尺度，在那里它被逮捕的稳定的熵分层;在一个特征的“浮力尺度”，能量被倾倒到大规模的g-模式，随后消散。因此，熵分层对湍流涡旋的大小和强度设置了上限。与此同时，尽管磁场的几何形状错综复杂，但MTI传递了相当大一部分热量。在一个配套文件中，这些结果被扩展到三维流，并比较观察到的真实的集群。
Determining the origin of turbulence in galaxy clusters, and quantifying its transport of heat, is an outstanding problem, with implications for our understanding of their thermodynamic history and structure. As the dilute plasma of the intracluster medium (ICM) is magnetized, heat and momentum travel preferentially along magnetic field lines. This anisotropy triggers a class of buoyancy instabilities that destabilize the ICM, and whose turbulent motions can augment or impede heat transport. We focus on the magneto-thermal instability (MTI), which may be active in the periphery of galaxy clusters. We aim to take a fresh look at the problem and construct a general theory that explains the MTI saturation mechanism and provides scalings and estimates for the turbulent kinetic energy, magnetic energy, and heat flux. We simulate MTI turbulence with a Boussinesq code,snoopy, which, in contrast to previous work, allows us to perform an extensive sampling of the parameter space. In two dimensions the saturation mechanism involves an inverse cascade that carries kinetic energy from the short MTI injection scales to larger scales, where it is arrested by the stable entropy stratification; at a characteristic ‘buoyancy scale’, the energy is dumped into large-scale g-modes, which subsequently dissipate. Consequently, the entropy stratification sets an upper limit on the size and strength of turbulent eddies. Meanwhile, the MTI conveys a substantial fraction of heat, despite the tangled geometry of the magnetic field. In a companion paper, these results are extended to three-dimensional flows, and compared to observations of real clusters.