Department of Astronomy, University of Bologna, Via Ranzani 1, 40127 Bologna, Italy.
Nature. 2009 Dec 24;462(7276):1028-31. doi: 10.1038/nature08607.
Stars in globular clusters are generally believed to have all formed at the same time, early in the Galaxy's history. 'Blue stragglers' are stars massive enough that they should have evolved into white dwarfs long ago. Two possible mechanisms have been proposed for their formation: mass transfer between binary companions and stellar mergers resulting from direct collisions between two stars. Recently the binary explanation was claimed to be dominant. Here we report that there are two distinct parallel sequences of blue stragglers in M 30. This globular cluster is thought to have undergone 'core collapse', during which both the collision rate and the mass transfer activity in binary systems would have been enhanced. We suggest that the two observed sequences are a consequence of cluster core collapse, with the bluer population arising from direct stellar collisions and the redder one arising from the evolution of close binaries that are probably still experiencing an active phase of mass transfer.
球状星团中的恒星通常被认为是在银河系历史早期的同一时间形成的。“蓝离散星”是指质量足够大的恒星，它们很久以前就应该进化成白矮星了。对于它们的形成，有两种可能的机制被提出：双星伴星之间的物质转移和两颗恒星直接碰撞导致的恒星合并。最近，二元解释被认为是占主导地位的。在这里，我们报告说，M30 中有两个截然不同的蓝离散星平行序列。这个球状星团被认为经历了“核心坍缩”，在这个过程中，双星系统中的碰撞率和物质转移活动都会增强。我们认为，这两个观测到的序列是星团核心坍缩的结果，较蓝的种群是由恒星的直接碰撞产生的，而较红的种群则是由可能仍处于活跃物质转移阶段的近双星的演化产生的。
