Magnetic-field evolution in a plastically failing neutron-star crust
Magnetic-field evolution in a plastically failing neutron-star crust
复制标题
塑性失效中子星地壳中的磁场演化
DOI：
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发表时间：
2019
影响因子：
4.8
通讯作者：
K. Gourgouliatos
中科院分区：
文献类型：
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作者：
S. K. Lander;K. Gourgouliatos
在中子星（NS）地壳的正常条件下，离子被锁定在地壳晶格中的适当位置，只有电子是移动的，因此磁场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，使地壳超过其弹性极限，并塑性流动。我们认为这种塑性流动的性质和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。我们进行数值的地壳磁场的霍尔漂移和欧姆衰减的联合作用下的演变，跟踪磁应力的积累，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，要使磁星日冕与小尺度的磁性特征共存，塑性流的粘度必须大约为1036-1037 g cm− 1 s −1。我们发现在表面有显著的运动，速率为10-100 cm/年，并且局部磁场比没有塑性流动的演化要弱。我们讨论天体物理的影响，以及如何我们的本地模拟可以用来建立一个全球模型的NS地壳场演化。
Under normal conditions in a neutron-star (NS) 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 1036–1037 g cm−1s−1. We find significant motion at the surface at a rate of 10–100 cm yr−1, and that the localized 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 NS crust.