恒星内部泰勒不稳定性的全球模拟：引力的稳定效应
Global simulations of Tayler instability in stellar interiors: The stabilizing effect of gravity
摘要：
揭示环向场不稳定性的演化，即泰勒不稳定性，对于理解早期型恒星、红巨星核心或任何恒星辐射带中观测到的磁场的强度和拓扑结构至关重要。我们要研究的非线性演化的不稳定性储存在一个稳定的分层层，在球对称和旋转的情况下的环形场。特别是，我们打算量化的Brunt-Väisäla（$ω_{\rm BV}$）和阿尔文（$ω_{\rm A}$）频率的函数的不稳定性的抑制。我们使用的MHD方程中实现的滞弹性近似的EULAG-MHD代码，并进行了大量的数值模拟的不稳定性探索的参数空间的$ω_{\rm BV}$和$ω_{\rm A}$。我们表明，超过临界值的重力强烈抑制的不稳定性，与线性分析。初始场的强度也起着重要的作用：较弱的场显示出慢得多的增长率。此外，在重力很低的情况下，增长最快的模式具有很大的特征径向尺度，与强重力的情况不同，在强重力的情况下，不稳定性的特点是水平位移。结果表明滞弹性近似可以有效地描述恒星内部环向场不稳定性的演化。由于$ω_{\rm BV}$值的增加，不稳定性被抑制，这可能有助于解释Ap/Bp星的磁沙漠，因为在强引力的情况下，弱场只是轻微地不稳定。
英文摘要：
Unveiling the evolution of toroidal field instability, known as Tayler instability, is essential to understand the strength and topology of the magnetic fields observed in early-type stars, in the core of the red giants, or in any stellar radiative zone. We want to study the non-linear evolution of the instability of a toroidal field stored in a stably stratified layer, in spherical symmetry and in the absence of rotation. In particular, we intend to quantify the suppression of the instability as a function of the Brunt-Väisäla ($ω_{\rm BV}$) and the Alfvén ($ω_{\rm A}$) frequencies. We use the MHD equations as implemented in the anelastic approximation in the EULAG-MHD code and perform a large series of numerical simulations of the instability exploring the parameter space for the $ω_{\rm BV}$ and $ω_{\rm A}$. We show that beyond a critical value gravity strongly suppress the instability, in agreement with the linear analysis. The intensity of the initial field also plays an important role: weaker fields show much slower growth rates. Moreover, in the case of very low gravity, the fastest growing modes have a large characteristic radial scale, at variance with the case of strong gravity, where the instability is characterized by horizontal displacements. Our results illustrate that the anelastic approximation can efficiently describe the evolution of toroidal field instability in stellar interiors. The suppression of the instability as a consequence of increasing values of $ω_{\rm BV}$ might play a role to explain the magnetic desert in Ap/Bp stars since weak fields are only marginally unstable in the case of strong gravity.
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