Three routes to jet collimation by the Balbus–Hawley magnetorotational instability
Three routes to jet collimation by the Balbus–Hawley magnetorotational instability
复制标题
巴尔布斯-霍利磁旋转不稳定性实现射流准直的三种途径
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发表时间：
2005
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影响因子：
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通讯作者：
P. Williams
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文献类型：
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作者：
P. Williams
最近，三种完全不同的工作导致了磁旋转不稳定性(MRI)可能会产生环状应力，从而准直喷流的结论。一种观点认为，一般而言，磁流体力学(MHD)湍流，特别是由核磁共振驱动的湍流，更接近于粘弹性，而不是粘性。另一个论点是基于核磁共振在一维模拟岩芯坍塌的情况下的色散关系。然而，第三个论点存在于塌陷星和厚吸积流的直接MHD数值模拟结果中。我详细阐述了我之前关于上述第一个论点的工作，并简要讨论了这三组结果是如何联系在一起的。我还讨论了磁张力和磁压在这项工作中所扮演的不同角色。我指出，这会导致考虑环向应力和径向应力之间的法向应力差，而不是只关注环向应力本身。此外，我认为，如果厚吸积流和塌陷星的模拟包含了MRI诱导的粘性应力的现象学模型，但忽略了这些MRI诱导的其他应力分量，那么它们就不是自洽的。我简要地评论了RHESSI在伽马射线暴GRB0212206.1中对极化的观测，认为这种极化与纠缠场是一致的，不需要大规模的有组织的场。最后，我建议，这里所描述的磁场在形成喷流中的作用，应该理解为不是在喷流的磁心模型的范围内工作，而是作为它们的替代。
Three completely different lines of work have recently led to the conclusion that the magnetorotational instability (MRI) may create a hoop stress that collimates jets. One argument is based upon consideration that magnetohydrodynamic (MHD) turbulence, in general, and turbulence driven by the MRI, in particular, is more nearly viscoelastic than it is viscous. Another argument is based upon the dispersion relation for the MRI in the context of 1 D simulations of core collapse. Yet a third argument rests in the results of direct numerical MHD simulations of collapsars and thick accretion flows. I elaborate on my previous work regarding the first argument above and I briefly discuss how these three sets of results are all related. I also discuss the different roles played by the magnetic tension and the magnetic pressure within the context of this work. I point out that this leads to consideration of the normal stress difference between the hoop stress and the radial stress, in preference to a focus on just the hoop stress itself. Additionally, I argue that simulations of thick accretion flows and collapsars are not self-consistent if they include a phenomenological model for an MRI-induced viscous stress but disregard these other MRI-induced stress components. I comment briefly on the RHESSI observation of polarization in the gamma-ray burst GRB0212206.1 argue that this polarization is consistent with a tangled field, and does not require a large-scale organized field. Finally, I suggest that the role of magnetic fields in creating jets, as described here, should be understood not to work within the confines of magnetocentrifugal models of jets, but rather as an alternative to them.