Non-ideal magnetohydrodynamic simulations of the first star formation: the effect of ambipolar diffusion
Non-ideal magnetohydrodynamic simulations of the first star formation: the effect of ambipolar diffusion
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第一个恒星形成的非理想磁流体动力学模拟：双极扩散的影响
DOI：
10.1093/mnras/stac3724
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发表时间：
2022
影响因子：
4.8
通讯作者：
Tomida Kengo
中科院分区：
文献类型：
--
作者：
Sadanari Kenji Eric;Omukai Kazuyuki;Sugimura Kazuyuki;Matsumoto Tomoaki;Tomida Kengo
在现今宇宙中，磁场在星星形成过程中扮演着角动量输运和外流驱动的重要角色，控制着星周盘的形成/碎裂以及星星的形成效率。虽然在早期宇宙中只存在一个弱得多的场，但最近的理论研究发现，在引力坍缩期间，湍流发电机可以产生强场。在这里，我们研究了云核的引力坍缩（）到原恒星形成（）的非理想磁流体动力学模拟考虑双极扩散（AD），占主导地位的非理想效应的原始气体。我们系统地研究了旋转云核，无论有或没有湍流，并与不同强度的均匀场渗透。我们发现，AD可以稍微抑制发电机的字段增长，特别是在规模小于在密度范围内的Jeans尺度，而我们不能看到AD的温度演变的效果，因为AD加热速率总是小于压缩加热。AD的低效率使得磁场与形成的原恒星一样强，比现在的情况强得多，即使在最初磁场很弱的情况下。磁场影响流入运动时，放大到均分的水平与湍流的琼斯规模，虽然扰动场不发射风。这可能意味着发电机放大场对吸积阶段后期的动力学影响要小于电离反馈等其他过程。
In the present-day universe, magnetic fields play such essential roles in star formation as angular momentum transport and outflow driving, which control circumstellar disc formation/fragmentation and also the star formation efficiency. While only a much weaker field has been believed to exist in the early universe, recent theoretical studies find that strong fields can be generated by turbulent dynamo during the gravitational collapse. Here, we investigate the gravitational collapse of a cloud core () up to protostar formation () by non-ideal magnetohydrodynamic simulations considering ambipolar diffusion (AD), the dominant non-ideal effects in the primordial-gas. We systematically study rotating cloud cores either with or without turbulence and permeated with uniform fields of different strengths. We find that AD can slightly suppress the field growth by dynamo especially on scales smaller than the Jeans-scale at the density range, while we could not see the AD effect on the temperature evolution, since the AD heating rate is always smaller than compression heating. The inefficiency of AD makes the field as strong asnear the formed protostar, much stronger than in the present-day cases, even in cases with initially weak fields. The magnetic field affects the inflow motion when amplified to the equipartition level with turbulence on the Jeans-scale, although disturbed fields do not launch winds. This might suggest that dynamo amplified fields have smaller impact on the dynamics in the later accretion phase than other processes such as ionization feedback.