Disc formation in magnetized dense cores with turbulence and ambipolar diffusion
Disc formation in magnetized dense cores with turbulence and ambipolar diffusion
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湍流和双极扩散下磁化致密核心中圆盘的形成
DOI：
10.1093/mnras/stz2436
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发表时间：
2019
影响因子：
4.8
通讯作者：
Zhao Bo
中科院分区：
文献类型：
--
作者：
Lam Ka Ho;Li Zhi-Yun;Chen Che-Yu;Tomida Kengo;Zhao Bo
圆盘对于恒星和行星的形成都是必不可少的，但它们如何在磁化分子云核心中形成仍然存在争议。这项工作的重点是如何光盘的形成是受湍流和双极扩散（AD），单独和组合，强调原恒星质量吸积阶段的星星形成。我们发现，一个相对较强的，在核心尺度上的声波湍流强烈扭曲，但不完全破坏众所周知的磁感应扁平伪光盘，占主导地位的内部原恒星吸积流在层流的情况下，与以前的工作。湍流使得能够在早期形成相对较大的圆盘，无论是否存在AD，但是这样的圆盘保持强烈磁化并且不会持续到我们的模拟结束，除非还存在相对较强的AD。层流模拟中启用AD的盘倾向于重力碎裂。初始湍流抑制了椎间盘碎裂。AD有利于磁盘的形成和生存，通过减少磁场强度在拱星区域通过磁通量重新分配，并使磁力线有较少的箍缩方位角，特别是在后期。我们的结论是，湍流和AD相互补充，促进椎间盘形成。在我们的模拟中形成的盘继承了来自其母核的相当强的磁场，具有几十个或更小的典型等离子体β，这比原行星盘的磁流体动力学模拟中通常采用的值低2-3个数量级。为了解决这一潜在的紧张局势，需要更长期的模拟光盘的形成和演变越来越现实的物理。
Discs are essential to the formation of both stars and planets, but how they form in magnetized molecular cloud cores remains debated. This work focuses on how the disc formation is affected by turbulence and ambipolar diffusion (AD), both separately and in combination, with an emphasis on the protostellar mass accretion phase of star formation. We find that a relatively strong, sonic turbulence on the core scale strongly warps but does not completely disrupt the well-known magnetically induced flattened pseudo-disc that dominates the inner protostellar accretion flow in the laminar case, in agreement with previous work. The turbulence enables the formation of a relatively large disc at early times with or without AD, but such a disc remains strongly magnetized and does not persist to the end of our simulation unless a relatively strong AD is also present. The AD-enabled discs in laminar simulations tend to fragment gravitationally. The disc fragmentation is suppressed by initial turbulence. The AD facilitates the disc formation and survival by reducing the field strength in the circumstellar region through magnetic flux redistribution and by making the field lines there less pinched azimuthally, especially at late times. We conclude that turbulence and AD complement each other in promoting disc formation. The discs formed in our simulations inherit a rather strong magnetic field from its parental core, with a typical plasma-β of order a few tens or smaller, which is 2–3 orders of magnitude lower than the values commonly adopted in magnetohydrodynamic simulations of protoplanetary discs. To resolve this potential tension, longer term simulations of disc formation and evolution with increasingly more realistic physics are needed.