发表机构
University of Illinois Urbana-Champaign; University of Arizona; National Center for Supercomputing Applications, University of Illinois Urbana-Champaign; Academy of Athens; University of the Ryukyus（伊利诺伊大学厄巴纳-香槟分校; 亚利桑那大学; 伊利诺伊大学厄巴纳-香槟分校国家超级计算应用中心; 雅典科学院; 琉球大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过长期GRMHD模拟发现，中子星混合磁场的动态稳定平衡态不唯一，保留初始条件记忆，但环向与极向振幅比呈现20%-40%的普适性。
AI 中文摘要
已知具有纯极向或纯环向磁场的中子星是不稳定的，并会演化为混合极向-环向位形。这些不稳定性最终状态仍知之甚少。该状态是否唯一，或者动态稳定位形是否保留初始条件的记忆，尚不清楚。在本工作中，我们对具有自洽混合极向和环向磁场的缓慢旋转中子星的平衡位形进行了长期、完全广义相对论磁流体动力学（GRMHD）模拟。我们的初始位形在初始磁化强度和磁场几何上有所不同。我们将初始平衡态演化数十个阿尔芬时间尺度，直至任何不稳定性充分饱和之后。利用从可视化到等离子体四电流结构以及已稳定磁场的矢量球谐分解等一系列诊断工具，我们表征了动态稳定、已稳定的磁平衡态的结构。我们发现，稳定后的位形并非唯一。相反，它们表现出多样的多极结构，其中高阶模式贡献显著。我们的发现表明，磁场初始条件存在记忆，且中子星不存在唯一的动态稳定磁场几何。然而，我们发现，在稳定位形的主体中，磁场环向与极向振幅的角度平均径向轮廓表现出一定程度的普适性，典型值在20%至40%之间。
英文摘要
Neutron stars endowed with purely poloidal or purely toroidal magnetic fields are known to be unstable, and settle into mixed poloidal-toroidal configurations. The end state of these instabilities is still poorly understood. It is unclear whether this state is unique or whether the dynamically stable configuration has memory of the initial conditions. In this work, we perform long-term, fully general relativistic magnetohydrodynamic simulations of equilibrium configurations of slowly rotating neutron stars endowed with self-consistent mixed poloidal and toroidal magnetic fields. Our initial configurations differ in their initial magnetization and magnetic field geometry. We evolve the initial equilibria for tens of Alfvén timescales until well after any instabilities have saturated. Employing an array of diagnostic tools from visualizations to the structure of the plasma four-current and a vector spherical harmonic decomposition of the settled magnetic fields, we characterize the structure of the dynamically stable, settled magnetic equilibria. We find that the settled configurations are not unique. Instead, they exhibit diverse multipolar structures, with higher-order modes contributing substantially. Our findings demonstrate that there is memory of the magnetic-field initial conditions, and that there is no unique dynamically stable magnetic-field geometry for neutron stars. Nevertheless, we find that the angle-averaged radial profile of the magnetic field toroidal to poloidal amplitude in the bulk of the settled configurations exhibits some degree of universality with typical values of order \(20\)--\(40\%\).
