Conditions for circumstellar disc formation - II. Effects of initial cloud stability and mass accretion rate
Conditions for circumstellar disc formation - II. Effects of initial cloud stability and mass accretion rate
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DOI：
10.1093/mnras/stw2256
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发表时间：
2016-12
影响因子：
4.8
通讯作者：
M. Machida;Tomoaki Matsumoto;S. Inutsuka
中科院分区：
文献类型：
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作者：
M. Machida;Tomoaki Matsumoto;S. Inutsuka
利用三维磁流体动力学模拟研究了强磁化云核中圆盘的形成，重点研究了初始云稳定性和质量吸积率的影响。初始云的稳定性大大改变了光盘的形成过程，即使是星前云具有相同的质量流量比。一个高的质量吸积率的盘形成区域实现在最初的不稳定的云，并在短时间内引入一个大的角动量到星周区域。原恒星周围的区域既有薄的下落包层，又有弱磁场，这两个因素都削弱了磁制动的效果。在这样的不稳定云中，旋转支撑盘的生长得到促进。相反，云在最初接近平衡状态时，质量和角动量的吸积率较低。角动量在原恒星形成之前被传输到外层。在原恒星形成后，星周区域有一个厚厚的下沉包层和一个强大的磁场，有效地制动了圆盘。结果，当初始云处于接近稳定的状态时，盘形成被抑制。初始云的密度分布也影响盘的形成过程。星前云密度均匀时，星盘的生长强烈依赖于初始条件，而星前云密度不均匀时，星盘的形成过程没有显著差异。
Disc formation in strongly magnetized cloud cores is investigated using a three-dimensional magnetohydrodynamic simulation with a focus on the effects of the initial cloud stability and the mass accretion rate. The initial cloud stability greatly alters the disc formation process even for prestellar clouds with the same mass-to-flux ratio. A high mass accretion rate on to the disc-forming region is realized in initially unstable clouds, and a large angular momentum is introduced into the circumstellar region in a short time. The region around the protostar has both a thin infalling envelope and a weak magnetic field, which both weaken the effect of magnetic braking. The growth of the rotation-supported disc is promoted in such unstable clouds. Conversely, clouds in an initially near-equilibrium state show lower accretion rates of mass and angular momentum. The angular momentum is transported to the outer envelope before protostar formation. After protostar formation, the circumstellar region has a thick infalling envelope and a strong magnetic field that effectively brakes the disc. As a result, disc formation is suppressed when the initial cloud is in a nearly stable state. The density distribution of the initial cloud also affects the disc formation process. Disc growth strongly depends on the initial conditions when the prestellar cloud has a uniform density, whereas there is no significant difference in the disc formation process in prestellar clouds with non-uniform densities.