AI 中文总结
本文用ELEPHANT代码模拟不同初始磁场的太阳丰度核心坍缩超新星，发现强初始磁场会减小增益区湍动能与涡量，磁场对斜压矢量的贡献超过流体动力学贡献，且涡度与磁场始终接近随机取向。
AI 中文摘要
核心坍缩超新星激波下方流体的对流湍流运动拉伸并放大了前身星的磁场，该磁场所含能量来源于流体对磁场做的功，而这部分功消耗了流体的动能与内能。除了与流体的能量交换外，磁场还通过对斜压矢量的贡献对流体产生反作用，进而影响流体的涡度。本文使用ELEPHANT代码，针对初始零龄主序质量为15和20倍太阳质量、金属丰度为太阳丰度且初始磁场为纯环向磁场（B₀=0、10¹⁰、10¹²高斯）的恒星，探究核心坍缩超新星中磁场与流体的相互作用。研究发现，在反弹后早期演化阶段，增益区的磁场并未增长到足以改变全局动力学的程度（改变幅度低于10%）；在初始磁场较强的模拟中，增益区流体的湍动能更小，但由于湍动能测量方法的局限性，具体的减少量尚不明确。模拟中，对流一旦开始，磁场结构会迅速形成大量缠结的通量绳，这使得磁场对斜压矢量的贡献大幅增加，超过流体动力学的贡献。尽管流体涡度和磁场遵循与磁场非常相似的输运方程，但在演化的每个阶段，两者始终接近随机取向。此外，与湍动能密切相关的涡量在初始磁场较强的模拟中被减小，这支持了磁场会减少流体湍流量的推论。
英文摘要
The convective turbulent motion of the fluid below the shock in a core-collapse supernova stretches and amplifies the magnetic field of the progenitor star. The energy contained in the field is sourced from the work done by the fluid on the field which comes at the expense of the fluid's kinetic and internal energy. In addition to the energy exchange with the fluid, the magnetic field also has a back-reaction upon the fluid via a contribution to the baroclinic vector and thus affects the fluid vorticity. In this paper we explore the interaction of the magnetic field with the fluid in core-collapse supernovae using the ELEPHANT code with solar-metallicity stars of 15 and 20 \msun zero-age main sequence mass and purely toroidal initial magnetic fields of $B_0 = 0, 10^{10}, and 10^{12}$~G. We find that the magnetic field in the gain region does not become so large that it alters the global dynamics above the 10% level in the early post-bounce evolution. The turbulent kinetic energy of the fluid in the gain region is smaller in simulations with a strong initial magnetic field, but the exact amount of reduction is uncertain due to limitations of the methods for measuring turbulent kinetic energy. The structure of the field in the simulations quickly becomes a tangled mass of flux ropes as soon as convection begins, which leads to a large magnetic field contribution to the baroclinic vector that dominates over the hydrodynamic contribution. Although governed by very similar transport equations to the magnetic field, the fluid vorticity and magnetic field are always close to being randomly aligned at every stage of the evolution. The enstrophy, which is seen to be closely associated with the turbulent kinetic energy, is found to be reduced in simulations with a strong initial magnetic field supporting the inference that the magnetic field reduces the amount of turbulence in the fluid.
CommentsAccepted for publication in Phys. Rev. D. 20 pages. 12 figures. Data behind figures available on zenodo
