Nonaxisymmetric instabilities of neutron star with toroidal magnetic fields
Nonaxisymmetric instabilities of neutron star with toroidal magnetic fields
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DOI：
10.1051/0004-6361/201016242
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发表时间：
2011-04
影响因子：
6.5
通讯作者：
K. Kiuchi;Shijun Yoshida;M. Shibata
中科院分区：
文献类型：
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作者：
K. Kiuchi;Shijun Yoshida;M. Shibata
上下文自然界中经常会产生具有强环向磁场的中子星。我们表明，等熵中子星与纯环向磁场是不稳定的对相互作用，帕克和/或泰勒不稳定性的环向磁场的配置无关。目标。本文的目的是阐明具有强环向磁场的中子星在非轴对称扰动下的稳定性。其动机来自于这样一个事实，即在磁驱动的超新星之后诞生的超磁化中子星、磁星和磁化质子中子星可能具有如此强的环形磁场。方法.长期，三维广义相对论磁流体动力学模拟进行，准备等熵中子星与环形磁场在平衡的初始条件。为了探索旋转对稳定性的影响，对非旋转和刚性旋转模型进行了模拟。结果我们发现出现的帕克和/或泰勒不稳定性的非旋转和旋转的模型。对于非旋转和旋转模型，帕克不稳定性是主要的不稳定性预测的局部线性摄动分析。在旋转模型中也出现了交换不稳定性。发现快速旋转不足以抑制帕克不稳定性，这一发现与扰动分析不一致。其原因是，刚性和快速旋转的恒星是边缘稳定的，因此，在恒星脉动的存在下，旋转轮廓的变形，具有负梯度的角动量轮廓的不稳定区域的发展。在不稳定性开始后，湍流被激发。与轴对称情况相反，在湍流发展之后，磁场永远不会达到平衡状态。结论.具有强环向磁场的等熵中子星很可能总是不稳定的，而不是帕克不稳定性。诱导湍流运动并维持很长时间。这一结论与轴对称模拟的结果不同，表明三维模拟对于探索磁星的形成或磁星的日珥活动（如巨型耀斑）是必不可少的。
Context. Neutron stars with strong toroidal magnetic fields are often produced in nature. We show that isentropic neutron stars with purely toroidal magnetic fields are unstable against the int erchange, Parker and/or Taylor instabilities irrespective of the toroidal magnetic field configurations. Aims. The aim of this paper is to clarify the stabilities of neutron stars with strong toroidal magnetic fields against non-axis ymmetric perturbation. The motivation comes from the fact that super magnetized neutron stars of∼ 10 15 G, magnetars, and magnetized protoneutron stars born after the magnetically-driven supernovae are likely to have such strong toroidal magnetic fields. Methods. Long-term, three-dimensional general relativistic magneto-hydrodynamic simulations are performed, preparing isentropic neutron stars with toroidal magnetic fields in equilibrium a s initial conditions. To explore the effects of rotations on the stability, simulations are done for both non-rotating and rigidly rotating models. Results. We find the emergence of the Parker and/or Tayler instabilities in both the non-rotating and rotati ng models. For both nonrotating and rotating models, the Parker instability is the primary instability as predicted by the local linear pertur bation analysis. The interchange instability also appears in the rotating models. It is found that rapid rotation is not enough to suppres s the Parker instability, and this finding does not agree with the perturb ation analysis. The reason for this is that rigidly and rapid ly rotating stars are marginally stable, and hence, in the presence of stellar pulsations by which the rotational profile is deformed, unst able regions with negative gradient of angular momentum profile is develo ped. After the onset of the instabilities, a turbulence is ex cited. Contrary to the axisymmetric case, the magnetic fields never reach an e quilibrium state after the development of the turbulence. Conclusions. Isentropic neutron stars with strong toroidal magnetic fiel ds are likely to be always unstable against the Parker instability. A turbulence motion is induced and maintained for a long time. This conclusion is different from that in axisymmetric simulations and suggests that three-dimensional simulation is indispensable for exploring the formation of magnetars or prominence activities of magnetars such as giant flares.