塑性破坏的中子星壳中的磁场演化
Magnetic-field evolution in a plastically-failing neutron-star crust
摘要：
在中子星地壳的正常情况下，离子被锁定在地壳晶格中，只有电子是移动的，因此磁场的演化与电子速度直接相关。然而，这种演化建立了磁应力，它可以变得足够大，使地壳超过其弹性限度，并塑性流动。我们考虑这种塑性流动的性质和对地壳磁场演化的反作用。我们制定了一个平面平行模型的本地故障，表明表面运动是不可避免的，一旦地壳产量，在没有额外的耗散机制。我们进行数值演化的地壳磁场霍尔漂移和欧姆衰减的联合作用下，跟踪磁应力的建立，并诊断地壳故障与冯米塞斯标准。在这一点之外，我们解决了塑性速度和磁场的耦合演化。我们的研究结果表明，有一个共存的磁星日冕与小规模的磁性功能，塑性流动的粘度必须大致为$10^{36}-10^{37}\ \textrm{g cm}^{-1}\textrm{s}^{-1}$。我们发现显着的运动在表面上的速度为$10-100$厘米，每年，和本地化的磁场是弱于没有塑性流动的演变。我们讨论了天体物理学的影响，以及如何使用我们的局部模拟来建立中子星地壳场演化的全球模型。
英文摘要：
Under normal conditions in a neutron-star crust, ions are locked in place in the crustal lattice and only electrons are mobile, and magnetic-field evolution is thus directly related to the electron velocity. The evolution, however, builds magnetic stresses that can become sufficiently large for the crust to exceed its elastic limit, and to flow plastically. We consider the nature of this plastic flow and the back-reaction on the crustal magnetic field evolution. We formulate a plane-parallel model for the local failure, showing that surface motions are inevitable once the crust yields, in the absence of extra dissipative mechanisms. We perform numerical evolutions of the crustal magnetic field under the joint effect of Hall drift and Ohmic decay, tracking the build-up of magnetic stresses, and diagnosing crustal failure with the von Mises criterion. Beyond this point we solve for the coupled evolution of the plastic velocity and magnetic field. Our results suggest that to have a coexistence of a magnetar corona with small-scale magnetic features, the viscosity of the plastic flow must be roughly $10^{36}-10^{37}\ \textrm{g cm}^{-1}\textrm{s}^{-1}$. We find significant motion at the surface at a rate of $10-100$ centimetres per year, and that the localised magnetic field is weaker than in evolutions without plastic flow. We discuss astrophysical implications, and how our local simulations could be used to build a global model of field evolution in the neutron-star crust.
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