恒星中轴对称磁场的稳定性
Stability of axially symmetric magnetic fields in stars
摘要：
在AP星、白矮星和中子星中观测到的磁场已知是长期稳定的。然而，恒星内部允许这些状态的物理条件仍然是一个研究问题。它已经正式证明，无论是纯环向和纯极向磁场发展不稳定性在某些点的恒星。另一方面，数值模拟证明了稳定层结恒星内部大致轴对称磁场位形的稳定性。这些配置包括相互稳定的环形和极向组件在一个扭曲的环面形状。先前的研究已经提出了粗略的上限和下限的比例的磁场能量的环向和极向分量的磁场。与映射出的参数空间下，这样的配置保持稳定的目的，我们使用的3D磁流体动力学模拟的磁场在非旋转，非简并的恒星，其中粘度是唯一的耗散机制，无论是一个统一的（正压）和径向增加（稳定分层）的特定熵的恒星的演变。此外，我们考虑了不同的条件下的稳定分层的程度和每个组件中的磁能，大致确认了先前提出的稳定边界的磁场。
英文摘要：
The magnetic fields observed in Ap-stars, white dwarfs, and neutron stars are known to be stable for long times. However, the physical conditions inside the stellar interiors that allow these states are still a matter of research. It has been formally demonstrated that both purely toroidal and purely poloidal magnetic fields develop instabilities at some point in the star. On the other hand, numerical simulations have proved the stability of roughly axisymmetric magnetic field configurations inside stably stratified stars. These configurations consist of mutually stabilizing toroidal and poloidal components in a twisted torus shape. Previous studies have proposed rough upper and lower bounds on the ratio of the magnetic energy in the toroidal and poloidal components of the magnetic field. With the purpose of mapping out the parameter space under which such configurations remain stable, we used the Pencil Code to perform 3D magnetohydrodynamic simulations of the evolution of the magnetic field in non-rotating, non-degenerate stars in which viscosity is the only dissipation mechanism, both for stars with a uniform (barotropic) and radially increasing (stably stratified) specific entropy. Furthermore, we considered different conditions regarding the degree of stable stratification and the magnetic energy in each component, roughly confirming the previously suggested stability boundaries for the magnetic field.
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