标题： 星团形成观测与理论 显示英文标题

标题： Observations and Theory of Star Cluster Formation

摘要： 年轻恒星在各种尺度上形成，产生具有不同程度引力自结合的聚集体和星团。松散的聚集体在空间和时间上都呈现出层次结构，类似于星际湍流，这表明这些恒星仅在几次湍流跨越时间内形成，其位置映射出之前的气体分布。另一方面，密集的星团常常混合得较好，仿佛自引力运动已经抹去了最初的精细结构。然而，一些最年轻的密集星团也显示出次聚类现象，因此可能所有恒星聚集都与湍流有关。某些最密集的星团也可能被触发形成。 综述了星团内恒星质量分离的证据以及对此效应的各种解释。还回顾了星团形成的理论其他方面，包括许多关于星团形成机制的具体提议。讨论了形成束缚星团的条件。如果气体去除过程缓慢且恒星以亚临界速度诞生，则临界恒星形成效率可以低至10%。环境条件，特别是压力，可能会影响最终成为束缚状态的星团的比例和质量。球状星团可能像普通的疏散星团一样形成，但在早期晕族和核球形成时的条件下，或者在今天相互作用和发生星爆的星系中形成。 总结了球状星团形成的几种理论。 显示英文摘要

摘要： Young stars form on a wide range of scales, producing aggregates and clusters with various degrees of gravitational self-binding. The loose aggregates have a hierarchical structure in both space and time that resembles interstellar turbulence, suggesting that these stars form in only a few turbulent crossing times with positions that map out the previous gas distribution. Dense clusters, on the other hand, are often well mixed, as if self-gravitational motion has erased the initial fine structure. Nevertheless, some of the youngest dense clusters also show sub-clumping, so it may be that all stellar clustering is related to turbulence. Some of the densest clusters may also be triggered. The evidence for mass segregation of the stars inside clusters is reviewed, along with various explanations for this effect. Other aspects of the theory of cluster formation are reviewed as well, including many specific proposals for cluster formation mechanisms. The conditions for the formation of bound clusters are discussed. Critical star formation efficiencies can be as low as 10% if the gas removal process is slow and the stars are born at sub-virial speeds. Environmental conditions, particularly pressure, may affect the fraction and masses of clusters that end up bound. Globular clusters may form like normal open clusters but in conditions that prevailed during the formation of the halo and bulge, or in interacting and starburst galaxies today. Various theories for the formation of globular clusters are summarized.