The origin and formation of the circumstellar disc
The origin and formation of the circumstellar disc
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DOI：
10.1111/j.1365-2966.2011.18349.x
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发表时间：
2010-08
影响因子：
4.8
通讯作者：
M. Machida;Tomoaki Matsumoto
中科院分区：
文献类型：
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作者：
M. Machida;Tomoaki Matsumoto
本文从星前阶段开始，通过对分子云核和原恒星的解析，研究了有磁场和无磁场时坍缩分子云中星周盘的形成和演化。在坍缩的云核中，第一个（绝热的）核心出现在原恒星形成之前。反映坍缩气体的热力学，第一个核心的质量比原恒星大得多。当分子云没有角动量时，第一个核心福尔斯落在原恒星上，并在原恒星形成几年后消失。另一方面，当分子云具有角动量时，即使在原恒星形成之后，第一核心也不会消失，而是直接演化成具有开普勒旋转的星周盘。星周盘的形成有两条途径。当初始云具有相当小的旋转能量时，在原恒星形成后不久就会出现两个嵌套的圆盘。在早期的主吸积阶段，内盘的大小增加，并与外盘（即第一个核心）合并，形成一个单一的星周盘与开普勒旋转。另一方面，当分子云具有与观测相当的旋转能量时，对应于第一个核心的单个离心支撑盘在原恒星形成之前已经存在。在这样的星云中，第一核心密度逐渐增加，维持开普勒自转，并在其中形成原恒星。磁场很少影响星周盘的早期形成，因为磁场消散在星周盘形成的高密度气体区域。因此，无论如何，原恒星在其形成时已经被一个巨大的星周盘所包围。在主要的吸积阶段，星周盘的质量大约是原恒星的10-100倍。这样的盘是形成双星伴星和气态巨行星的有利场所。
The formation and evolution of the circumstellar disc in the collapsing molecular cloud with and without magnetic field is investigated from the pre-stellar stage resolving both the molecular cloud core and the protostar itself. In the collapsing cloud core, the first (adiabatic) core appears prior to the protostar formation. Reflecting the thermodynamics of the collapsing gas, the first core is much more massive than the protostar. When the molecular cloud has no angular momentum, the first core falls on to the protostar and disappears a few years after the protostar formation. On the other hand, when the molecular cloud has an angular momentum, the first core does not disappear even after the protostar formation, and directly evolves into the circumstellar disc with a Keplerian rotation. There are two paths for the formation of the circumstellar disc. When the initial cloud has a considerably small rotational energy, two nested discs appear just after the protostar formation. During the early main accretion phase, the inner disc increases its size and merges with the outer disc (i.e. first core) to form a single circumstellar disc with a Keplerian rotation. On the other hand, when the molecular cloud has a rotational energy comparable to observations, a single centrifugally supported disc that corresponds to the first core already exists prior to the protostar formation. In such a cloud, the first core density gradually increases, maintaining the Keplerian rotation and forms the protostar inside it. The magnetic field rarely affects the early formation of the circumstellar disc because the magnetic field dissipates in the high-density gas region where the circumstellar disc forms. As a result, in any case, the protostar at its formation is already surrounded by a massive circumstellar disc. The circumstellar disc is about 10–100 times more massive than the protostar in the main accretion phase. Such discs are favourable sites for the formation of binary companions and gas-giant planets.