外馈星形成的数值研究
Externally Fed Star Formation: A Numerical Study
摘要：
我们调查，通过一系列的数值计算，致密的核心，吸积外部气体的恒星形成点和超越的演变。我们的模型云是球形的，非磁化的配置与固定的外边界，气体进入亚音速。当我们从任何接近平衡态开始时，我们发现云的内部速度在很长一段时间内也保持亚音速，这与观测结果一致。然而，在恒星形成前不久，速度变成超音速。因此，形成原恒星的吸积速率远大于基准值cs ^3/G，其中cs是致密核心中的声速。这种吸积尖峰将产生比即使是嵌入最多的年轻恒星更高的光度。此外，我们发现围绕原恒星的超音速下沉区域会迅速吞噬大部分云，这再次违反了观测结果，即下沉是空间受限的。类似的问题的结果已经获得了所有其他的流体动力学模拟的日期，无论具体的降落几何形状或采用的边界条件。低质量恒星的形成显然是一个准静态的过程，其中云气体以亚音速向内移动，直到恒星本身诞生。我们推测，在云的内部深处的磁张力有助于抑制在此事件之前的下降。
英文摘要：
We investigate, through a series of numerical calculations, the evolution of dense cores that are accreting external gas up to and beyond the point of star formation. Our model clouds are spherical, unmagnetized configurations with fixed outer boundaries, across which gas enters subsonically. When we start with any near-equilibrium state, we find that the cloud's internal velocity also remains subsonic for an extended period, in agreement with observations. However, the velocity becomes supersonic shortly before the star forms. Consequently, the accretion rate building up the protostar is much greater than the benchmark value c_s^3/G, where c_s is the sound speed in the dense core. This accretion spike would generate a higher luminosity than those seen in even the most embedded young stars. Moreover, we find that the region of supersonic infall surrounding the protostar races out to engulf much of the cloud, again in violation of the observations, which show infall to be spatially confined. Similar problematic results have been obtained by all other hydrodynamic simulations to date, regardless of the specific infall geometry or boundary conditions adopted. Low-mass star formation is evidently a quasi-static process, in which cloud gas moves inward subsonically until the birth of the star itself. We speculate that magnetic tension in the cloud's deep interior helps restrain the infall prior to this event.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
