Departments of Physics and Astronomy, and Theoretical Astrophysics Center, University of California, Berkeley, California 94720-7300, USA.
Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-8169, USA.
Nature. 2017 Nov 2;551(7678):80-84. doi: 10.1038/nature24453. Epub 2017 Oct 16.
The cosmic origin of elements heavier than iron has long been uncertain. Theoretical modelling shows that the matter that is expelled in the violent merger of two neutron stars can assemble into heavy elements such as gold and platinum in a process known as rapid neutron capture (r-process) nucleosynthesis. The radioactive decay of isotopes of the heavy elements is predicted to power a distinctive thermal glow (a 'kilonova'). The discovery of an electromagnetic counterpart to the gravitational-wave source GW170817 represents the first opportunity to detect and scrutinize a sample of freshly synthesized r-process elements. Here we report models that predict the electromagnetic emission of kilonovae in detail and enable the mass, velocity and composition of ejecta to be derived from observations. We compare the models to the optical and infrared radiation associated with the GW170817 event to argue that the observed source is a kilonova. We infer the presence of two distinct components of ejecta, one composed primarily of light (atomic mass number less than 140) and one of heavy (atomic mass number greater than 140) r-process elements. The ejected mass and a merger rate inferred from GW170817 imply that such mergers are a dominant mode of r-process production in the Universe.
重元素（比铁重的元素）的宇宙起源长期以来一直不确定。理论模型表明，在两颗中子星剧烈合并过程中被抛出的物质可以通过一种称为快速中子捕获（r 过程）核合成的过程，组装成金和铂等重元素。预测重元素的同位素放射性衰变将为独特的热辉光（“千新星”）提供动力。对引力波源 GW170817 的电磁对应物的发现代表了首次有机会探测和仔细研究新合成的 r 过程元素样本的机会。在这里，我们报告了详细预测千新星电磁发射的模型，并使我们能够从观测中得出抛射物的质量、速度和组成。我们将这些模型与 GW170817 事件相关的光学和红外辐射进行比较，以证明观测到的源是千新星。我们推断出抛射物存在两个不同的成分，一个主要由轻（原子质量数小于 140）元素组成，另一个由重（原子质量数大于 140）r 过程元素组成。从 GW170817 推断出的抛射物质量和合并率表明，这种合并是宇宙中 r 过程产生的主要模式。
