Origin of the heavy elements in binary neutron-star mergers from a gravitational wave event

TL;DR

This paper models the electromagnetic emission from neutron star mergers to identify the origin of heavy elements, confirming such mergers as a major source of r-process elements like gold and platinum in the universe.

Contribution

It introduces detailed models linking kilonova emissions to ejecta properties, providing evidence that neutron star mergers are a primary source of heavy r-process elements.

Findings

Identification of two distinct ejecta components, light and heavy r-process elements.

Estimation of ejecta mass and velocity from GW170817 observations.

Support for neutron star mergers as dominant r-process element producers.

Abstract

The cosmic origin of the 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 detailed electromagnetic emission of kilonovae and enable the mass, velocity and composition of ejecta to be derived from the observations. We compare the models to the optical and infrared radiation associated with 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. Inferring the ejected mass and a merger rate from GW170817 implies that such mergers are a dominant mode of r-process production in the Universe.