University of Southampton, School of Physics and Astronomy, Southampton SO17 1BJ, UK.
Nature. 2011 Nov 9;479(7373):372-5. doi: 10.1038/nature10529.
Two types of supernova are thought to produce the overwhelming majority of neutron stars in the Universe. The first type, iron-core-collapse supernovae, occurs when a high-mass star develops a degenerate iron core that exceeds the Chandrasekhar limit. The second type, electron-capture supernovae, is associated with the collapse of a lower-mass oxygen-neon-magnesium core as it loses pressure support owing to the sudden capture of electrons by neon and/or magnesium nuclei. It has hitherto been impossible to identify the two distinct families of neutron stars produced in these formation channels. Here we report that a large, well-known class of neutron-star-hosting X-ray pulsars is actually composed of two distinct subpopulations with different characteristic spin periods, orbital periods and orbital eccentricities. This class, the Be/X-ray binaries, contains neutron stars that accrete material from a more massive companion star. The two subpopulations are most probably associated with the two distinct types of neutron-star-forming supernova, with electron-capture supernovae preferentially producing systems with short spin periods, short orbital periods and low eccentricities. Intriguingly, the split between the two subpopulations is clearest in the distribution of the logarithm of spin period, a result that had not been predicted and which still remains to be explained.
据认为，有两种类型的超新星会在宇宙中产生绝大多数的中子星。第一种是铁核塌缩超新星，发生在一颗高质量恒星形成一个超过钱德拉塞卡极限的简并铁核时。第二种是电子捕获超新星，与较低质量的氧氖镁核的坍缩有关，当它由于氖和/或镁核的突然电子捕获而失去压力支撑时，就会发生这种情况。迄今为止，还不可能识别出这两种形成渠道中产生的两种截然不同的中子星家族。在这里，我们报告说，一类大型的、众所周知的中子星宿主 X 射线脉冲星实际上由两个具有不同特征自旋周期、轨道周期和轨道偏心率的不同子群组成。这个名为 Be/X 射线双星的类别包含了从更大伴星吸积物质的中子星。这两个子群很可能与两种不同类型的形成中子星的超新星有关，电子捕获超新星更倾向于产生具有短自旋周期、短轨道周期和低偏心率的系统。有趣的是，两个子群之间的分裂在自旋周期对数的分布中最为明显，这一结果是以前没有预测到的，仍有待解释。
