Effect of Magnetic Braking on Circumstellar Disk Formation in a Strongly Magnetized Cloud
Effect of Magnetic Braking on Circumstellar Disk Formation in a Strongly Magnetized Cloud
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DOI：
10.1093/pasj/63.3.555
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发表时间：
2010-09
影响因子：
2.3
通讯作者：
M. Machida;S. Inutsuka;Tomoaki Matsumoto
中科院分区：
文献类型：
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作者：
M. Machida;S. Inutsuka;Tomoaki Matsumoto
利用电阻磁流体力学模拟，我们考虑了强磁化云中星周盘的形成。初始状态采用孤立云核嵌入低密度均匀磁场的星际介质中。云的演化经过计算，直到几乎所有初始云内的气体落在星周盘或一颗原恒星上，一部分气体被星周盘驱动的原恒星流出物喷射到星际介质中。在早期的主吸积阶段，由于星周盘的角动量被磁制动和原恒星流出物有效地转移，盘的大小被限制在- 10 AU。然而，在主吸积阶段后期，星周盘迅速增长，在主吸积阶段结束时超过了100 AU。星周盘的快速增长是由流入包络层的耗尽引起的，而当流入包络层的质量大于星周盘时，磁制动是有效的。当星周盘的质量大于星周盘时，下降的包络层不能使其断裂。此外，原恒星的外流减弱并在后期的主吸积阶段消失，因为外流是由气体吸积到星周盘上提供动力的。虽然在磁化云中形成的星周盘比在非磁化云中形成的要小得多，但即使在强磁化云中也可以形成超过100 AU的星周盘。
Using resistive magnetohydrodynamics simulation, we consider circumstellar disk formation in a strongly magnetized cloud. As the initial state, an isolated cloud core embedded in a low-density interstellar medium with a uniform magnetic field was adopted. The cloud evolution was calculated until almost all gas inside the initial cloud fell onto either the circumstellar disk or a protostar, and a part of the gas was ejected into the interstellar medium by the protostellar outflow driven by the circumstellar disk. In the early main accretion phase, the disk size is limited to � 10 AU because the angular momentum of the circumstellar disk is effectively transferred by both magnetic braking and the protostellar outflow. In the later main accretion phase, however, the circumstellar disk grows rapidly and exceeds & 100 AU by the end of the main accretion phase. This rapid growth of the circumstellar disk is caused by depletion of the infalling envelope, while magnetic braking is effective when the infalling envelope is more massive than the circumstellar disk. The infalling envelope cannot brake the circumstellar disk when the latter is more massive than the former. In addition, the protostellar outflow weakens and disappears in the later main accretion phase, because the outflow is powered by gas accretion onto the circumstellar disk. Although the circumstellar disk formed in a magnetized cloud is considerably smaller than that in an unmagnetized cloud, a circumstellar disk exceeding 100 AU can form even in a strongly magnetized cloud.