Magnetic fields in the formation of the first stars.--II Results
Magnetic fields in the formation of the first stars.--II Results
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第一批恒星形成过程中的磁场。--II 结果
DOI：
10.1093/mnras/stac372
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
P. Li
中科院分区：
文献类型：
--
作者：
A. Stacy;C. McKee;Aaron T. Lee;R. Klein;P. Li
从z = 100的宇宙学初始条件开始，我们模拟了磁场对第III星族星形成的影响，并将我们的结果与论文I的预测进行了比较。我们使用gadget-2来跟踪系统在弱场时的演化。我们介绍了一种新的方法来治疗运动学领域的跟踪变形张量的演变。在这一阶段的模拟的增长率低于预期的扩散天体物理等离子体，具有非常低的电阻率（高磁普朗特数），我们归因于模拟中的大数值电阻率，对应于磁普朗特数的顺序统一。当磁场开始在z = 27的minihalo的核心动态显着，我们将其映射到一个统一的网格，并遵循自适应网格细化，MHD模拟猎户座2的演变。在orion 2模拟中，场的非线性演化违反了通量冻结，与Xu & Lazarian提出的理论一致。在密度为10 - 10 cm-3时，场接近动能均分。当在没有磁场的猎户座2中进行同样的计算时，会形成几颗原恒星，质量从101到30 M <$m不等;在有磁场的情况下，到模拟结束时只会形成一颗101到30 M <$m的原恒星。因此，磁场抑制了低质量Pop III星的形成，产生了头重脚轻的Pop III IMF，并导致了观测不到Pop III星。
Beginning with cosmological initial conditions at z = 100, we simulate the effects of magnetic fields on the formation of Population III stars and compare our results with the predictions of Paper I. We use gadget-2 to follow the evolution of the system while the field is weak. We introduce a new method for treating kinematic fields by tracking the evolution of the deformation tensor. The growth rate in this stage of the simulation is lower than expected for diffuse astrophysical plasmas, which have a very low resistivity (high magnetic Prandtl number); we attribute this to the large numerical resistivity in simulations, corresponding to a magnetic Prandtl number of order unity. When the magnetic field begins to be dynamically significant in the core of the minihalo at z = 27, we map it onto a uniform grid and follow the evolution in an adaptive mesh refinement, MHD simulation in orion2. The nonlinear evolution of the field in the orion2 simulation violates flux-freezing and is consistent with the theory proposed by Xu & Lazarian. The fields approach equipartition with kinetic energy at densities ∼ 10 − 10 cm. When the same calculation is carried out in orion2 with no magnetic fields, several protostars form, ranging in mass from ∼ 1 to 30 M⊙; with magnetic fields, only a single ∼ 30 M⊙ protostar forms by the end of the simulation. Magnetic fields thus suppress the formation of low-mass Pop III stars, yielding a top-heavy Pop III IMF and contributing to the absence of observed Pop III stars.