Centrally concentrated star formation in young clusters

The study of star cluster evolution necessitates modeling how their density profiles develop from their natal gas distribution. Observational evidence indicates that many star clusters follow a Plummer-like density profile. However, most studies have focused on the phase after gas ejection, neglecting the influence of gas on early dynamical evolution. We investigate the development of star clusters forming within gas clouds, particularly those with a centrally concentrated gas profile. Simulations were conducted using the Torch framework, integrating the FLASH magnetohydrodynamics code into AMUSE. This permitted detailed modeling of star formation, stellar evolution, stellar dynamics, radiative transfer, and gas magnetohydrodynamics. We study the collapse of centrally concentrated, turbulent spheres with a total mass of 2.5 × 103 M⊙, investigating the effects of varying numerical resolution and star formation scenarios. The free-fall time is shorter at the center than at the edges of the cloud, with a minimum value of 0.55 Myr. The key conclusions from this study are: (1) the final stellar density profile is more centrally concentrated than was analytically predicted, reflecting the role of global gas collapse and feedback; (2) subclusters can initially form even in centrally concentrated gas clouds; (3) gas collapses globally toward the center on the central free-fall timescale, contradicting the assumption in analytical models of local fragmentation and star formation; and (4) the mass of the most massive star formed is directly correlated with the cluster effective radius and inversely correlated with the velocity dispersion, while the duration of star formation correlates with the star formation efficiency.FullText for HTML: https://doi.org/10.1051/0004-6361/202556268

恒星团演化研究亟需对其密度轮廓从原生气体分布中的演化过程开展建模。观测证据表明，多数恒星团遵循类普朗莫（Plummer）密度轮廓。然而，绝大多数现有研究仅聚焦于气体被抛射后的演化阶段，忽略了气体对恒星团早期动力学演化的影响。本研究针对气体云内形成的恒星团展开探究，尤其关注那些气体轮廓呈中心集中分布的系统。本研究采用Torch框架开展数值模拟，将FLASH磁流体力学代码集成至AMUSE平台，该集成方案支持对恒星形成、恒星演化、恒星动力学、辐射转移以及气体磁流体力学过程开展精细化建模。本研究针对总质量为2.5×10³倍太阳质量（M⊙）的中心集中式湍流球的坍缩过程展开分析，探究不同数值分辨率与恒星形成场景对坍缩过程的影响。气体云中心区域的自由下落时间短于边缘区域，最短自由下落时间为0.55百万年（Myr）。本研究得到核心结论如下：(1) 最终恒星密度轮廓较理论解析预测结果更为中心集中，这一现象反映了整体气体坍缩与反馈过程的作用；(2) 即便在气体轮廓呈中心集中分布的云团中，子星团仍可在演化早期形成；(3) 气体以中心自由下落时标整体向中心坍缩，这与解析模型中关于局部分裂与恒星形成的假设相悖；(4) 形成的大质量恒星质量与星团有效半径呈正相关，与速度弥散呈负相关；而恒星形成持续时长则与恒星形成效率呈相关性。HTML全文链接：https://doi.org/10.1051/0004-6361/202556268