Magnetic inhibition of centrifugal instability
Magnetic inhibition of centrifugal instability
复制标题
离心不稳定性的磁抑制
DOI：
--
复制
发表时间：
2019
影响因子：
4.8
通讯作者：
J. Matsumoto
中科院分区：
文献类型：
--
作者：
S. Komissarov;K. Gourgouliatos;J. Matsumoto
最近的研究表明，离心不稳定性在受外部压力约束的天体物理射流动力学中可能是重要的。然而，这些研究仅限于非磁化流的情况。在这里，我们将探讨磁场在牛顿和相对论框架中的作用。由于射流问题相当复杂，我们将重点放在与射流问题有很大相似之处的圆柱旋转和轴向磁场的简单问题上，并且只考虑轴对称摄动。所研究的平衡构型包括一个圆柱形界面，除了该界面外，它们对非磁性离心和磁旋转不稳定都是稳定的。我们采用启发式方法推导了磁情况下界面的局部稳定性判据，并通过数值模拟验证了磁场的作用。理论和模拟结果与牛顿模型相当一致，但在界面处旋转运动的高洛伦兹因子极限上，与相对论模型存在潜在的差异。一般来说，磁场设定了一个临界波长，在这个波长以下离心模式是稳定的。我们讨论了我们的发现对天体物理喷流的影响，这表明离心不稳定性只在相对低磁化的喷流中发展。也就是说，磁压力必须低于热压力，而在相对论的情况下，喷流必须以动能为主。
Recently, it was shown that the centrifugal instability may be important in the dynamics of astrophysical jets undergoing reconfinement by external pressure. However, these studies were limited to the case of unmagnetized flows. Here, we explore the role of the magnetic field within both the Newtonian and relativistic frameworks. Since the jet problem is rather complicated, we focus instead on the simpler problem of cylindrical rotation and axial magnetic field, which shares significant similarity with the jet problem, and consider only axisymmetric perturbations. The studied equilibrium configurations involve a cylindrical interface and they are stable to non-magnetic centrifugal and magnetorotational instabilities everywhere except this interface. We use a heuristic approach to derive the local stability criterion for the interface in the magnetic case and numerical simulations to verify the role of the magnetic field. The theory and simulations agree quite well for Newtonian models but indicate a potential discrepancy for the relativistic models in the limit of high Lorentz factor of the rotational motion at the interface. In general, the magnetic field sets a critical wavelength below which the centrifugal modes are stabilized. We discuss the implication of our findings for the astrophysical jets, which suggest that the centrifugal instability develops only in jets with relatively low magnetization. Namely, the magnetic pressure has to be below the thermal one and for the relativistic case the jets have to be kinetic-energy dominated.