大块星系际等离子体中的抑制有效粘性
Suppressed effective viscosity in the bulk intergalactic plasma
摘要：
星系团中炽热的星系际等离子体的传输特性，如粘性和热传导，在很大程度上是未知的。虽然对于实验室等离子体，这些特征来自气体密度和温度，但由于粒子碰撞率低和磁场弱，星系际等离子体的配方可能根本不同。在数值模拟中，人们经常通过将这些等离子体建模为流体动力学流体来突破这些未知数，即使在集群中观察到的局部非流体动力学特征与这一假设相矛盾。使用深钱德拉观测后发座星系团，我们探测星系际介质中的气体波动下降到空间尺度的运输过程应该显着表现自己-至少如果纯库仑碰撞率的流体动力学模型确实是足够的。我们发现，他们没有，这意味着有效的各向同性粘度的数量级小于天真的预期。这表明在等离子体中由于粒子散射等离子体不稳定性引起的微波动，或运输过程是各向异性相对于本地磁场的碰撞率增强。因此，高雷诺数的数值模型似乎与观测结果更一致。我们的研究结果还表明，在集群中的湍流观测正在成为天体物理学的一个分支，可以提高对这种等离子体的理论观点。
英文摘要：
Transport properties, such as viscosity and thermal conduction, of the hot intergalactic plasma in clusters of galaxies, are largely unknown. While for laboratory plasmas these characteristics are derived from the gas density and temperature, such recipes can be fundamentally different for the intergalactic plasma due to a low rate of particle collisions and a weak magnetic field. In numerical simulations, one often cuts through these unknowns by modeling these plasmas as hydrodynamic fluids, even though local, non-hydrodynamic features observed in clusters contradict this assumption. Using deep Chandra observations of the Coma Cluster, we probe gas fluctuations in intergalactic medium down to spatial scales where the transport processes should prominently manifest themselves - at least if hydrodynamic models with pure Coulomb collision rates were indeed adequate. We find that they do not, implying that the effective isotropic viscosity is orders of magnitude smaller than naively expected. This indicates an enhanced collision rate in the plasma due to particle scattering off microfluctuations caused by plasma instabilities, or that the transport processes are anisotropic with respect to local magnetic field. For that reason, numerical models with high Reynolds number appear more consistent with observations. Our results also demonstrate that observations of turbulence in clusters are becoming a branch of astrophysics that can sharpen theoretical views on such plasmas.
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