arXiv 0904.35682009-04-22astro-ph.SR

超音速流中原恒星的形成：球形核的生长和坍缩

Protostar Formation in Supersonic Flows: Growth and Collapse of Spherical Cores

Hao Gong, Eve C. Ostriker

备注：: 41 pages, 14 figures, accepted for publication in ApJ
发表信息：: Astrophys.J.699:230-244,2009
DOI：: 10.1088/0004-637X/699/1/230

摘要：

我们提出了一个统一的模型，分子核心的形成和演变，基于收敛，超音速流的数值模拟。我们的模型适用于大尺度湍流主导的GMC中的恒星形成，包括四个主要阶段：核心建设，核心崩溃，信封下降，和后期吸积。在构造阶段，核心由密集的激波后气体形成，随着时间的推移，随着质量的增长，核心变得越来越集中分层。当定义核心边界的激波半径超过$R\approx 4 a (4πG ρ_{mean})^{-1/2}$（其中$a$是等温声速）时，坍缩波从边缘传播到中心。在建筑和坍塌阶段，密度分布可以用Bonnor-Ebert分布拟合，温度为真实值的1.2 - 2.9倍。正如先前发现的初始静态平衡，由外向内的崩溃导致拉尔森-潘斯顿密度分布$ρ\approx 8.86 a^2/(4 πG r^2)$。第三阶段，由引力稀疏的内-外波组成，导致$ρ\propto r^{-3/2}$，$v\propto r^{-1/2}$，也类似于舒最初描述的初始静态球体。我们发现，崩溃和陷落阶段具有可比的持续时间，$\sim t_{ff}$，与观测到的星前和原恒星（0/I类）核心的估计一致。核心构建需要更长的时间，但直到崩溃前不久才产生高对比度的对象。随着来流马赫数的增加，达到堆芯坍塌的时间和坍塌时的堆芯质量减小。在所有情况下，早期的吸积速率都是$\gg a^3/G$，但会急剧下降;最终的系统质量取决于后期吸积的持续时间，这是由云中的大尺度条件决定的。

英文摘要：

We present a unified model for molecular core formation and evolution, based on numerical simulations of converging, supersonic flows. Our model applies to star formation in GMCs dominated by large-scale turbulence, and contains four main stages: core building, core collapse, envelope infall, and late accretion. During the building stage, cores form out of dense, post-shock gas, and become increasingly centrally stratified as the mass grows over time. When the shock radius defining the core boundary exceeds $R\approx 4 a (4πG ρ_{mean})^{-1/2}$, where $a$ is the isothermal sound speed, a wave of collapse propagates from the edge to the center. During the building and collapse stages, density profiles can be fit by Bonnor-Ebert profiles with temperature 1.2 - 2.9 times the true value. As found previously for initially static equilibria, outside-in collapse leads to a Larson-Penston density profile $ρ\approx 8.86 a^2/(4 πG r^2)$. The third stage, consisting of an inside-out wave of gravitational rarefaction leading to $ρ\propto r^{-3/2}$, $v\propto r^{-1/2}$, is also similar to that for initially-static spheres, as originally described by Shu. We find that the collapse and infall stages have comparable duration, $\sim t_{ff}$, consistent with estimates for observed prestellar and protostellar (Class 0/I) cores. Core building takes longer, but does not produce high-contrast objects until shortly before collapse. The time to reach core collapse, and the core mass at collapse, decrease with increasing inflow Mach number. For all cases the accretion rate is $\gg a^3/G$ early on but sharply drops off; the final system mass depends on the duration of late-stage accretion, set by large-scale conditions in a cloud.

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英文摘要：

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