Evolution of First Cores and Formation of Stellar Cores in Rotating Molecular Cloud Cores
Evolution of First Cores and Formation of Stellar Cores in Rotating Molecular Cloud Cores
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DOI：
10.1086/523888
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发表时间：
2008-02
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通讯作者：
K. Saigo;K. Tomisaka;Tomoaki Matsumoto
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作者：
K. Saigo;K. Tomisaka;Tomoaki Matsumoto
假设正压状态方程，采用三维流体力学模拟方法，对不同旋转速度和密度挫折下的云核坍缩过程进行了模拟，考察了从旋转分子云核到恒星核的综合演化路径。我们发现演化路径只依赖于初始云核的角速度Ωc0。这些演化路径与Saigo和Tomisaka的准平衡轴对称模型和Bate的SPH计算的预测一致。进化路径定性地分为三种类型。(1)缓慢旋转的云团（Ωc0 < 0.01/tff = 0.05(ρc0/10−19 g cm−3)1/2 rad Myr−1）呈球型演化，其中ρc0为初始中心密度。这样的云形成了一个主要由热压支撑的第一核心。第一个核心的质量很小，为Mcore ~ 0.01 M☉，寿命也很短，只有×100年。在H2解离密度ρ≃5.6 ×10−8 g cm−3之后，它开始了第二次塌缩，整个核心在几个自由下落的时间尺度内吸积到恒星核心/盘上。(2) 0.01/tff < Ωc0 > 0.05/tff的旋转云呈现盘状演化。在这种情况下，第一个核心变成一个离心支持的大质量圆盘，其核心质量约为× 0.01-0.1 M☉，寿命为几千年。第一个核心对非轴对称动力不稳定是不稳定的，形成螺旋臂。重力转矩通过螺旋结构将角动量从中心区域提取到第一核心的外区域。在超过解离密度后，只有含有r ~ 1 AU的中心部分开始第二次坍缩。然而，在恒星核心形成后，外层残余盘保持其离心平衡。似乎第一个核心的残余物应该控制新生恒星系统的质量和角动量的吸积。(3) 0.05/tff > Ωc0的旋转云在第一核心阶段趋向于分裂成双星或多星。
We followed the collapse of cloud cores with various rotation speed and density frustrations using three-dimensional hydrodynamical simulations by assuming a barotropic equation of state and examined the comprehensive evolution paths from the rotation molecule cloud core to stellar core. We found that the evolutionary paths depend only on the angular velocity of initial cloud core Ωc0. These evolutionary paths agree well with predictions of Saigo and Tomisaka’s quasi-equilibrium axisymmetric models and SPH calculations of Bate. Evolutionary paths are qualitatively classified into three types. (1) A slowly rotating cloud with Ωc0 < 0.01/tff = 0.05(ρc0/10−19 g cm −3)1/2 rad Myr −1 shows spherical-type evolution, where ρc0 is the initial central density. Such a cloud forms a first core which is mainly supported by the thermal pressure. The first core has a small mass of Mcore ∼ 0.01 M☉ and a short lifetime of a few ×100 yr. After exceeding the H2 dissociation density ρ ≃ 5.6 × 10−8 g cm −3, it begins the second collapse, and the whole of the first core accretes onto the stellar core/disk within a few free-fall timescales. (2) A rotating cloud with 0.01/tff < Ωc0≲ 0.05/tff shows disk-type evolution. In this case, the first core becomes a centrifugally supported massive disk with Mcore ∼ a few × 0.01–0.1 M☉ and the lifetime is a few thousand years. The first core is unstable against nonaxisymmetric dynamic instability and forms spiral arms. The gravitational torque through spiral structure extracts angular momentum from the central region to the outer region of the first core. And only a central part with r ∼ 1 AU begins the second collapse after exceeding dissociation density. However, the outer remnant disk keeps its centrifugal balance after stellar core formation. It seems that this remnant of the first core should control the mass and angular momentum accretion onto the newborn stellar system. (3) A rotating cloud with 0.05/tff≲ Ωc0 tends to fragment into binary or multiple during the first core phase.