Binary neutron star (NS) mergers are promising sites of rapid neutron capture nucleosynthesis.
The explosion that results from the merger of two neutron stars spirals inward and creates a significant portion of the heavy components that make up our universe. The first instance of this process was a 2017 occurrence called GW 170817. Except for strontium, found in the optical spectrum, scientists have not been able to determine the precise elements produced in neutron star mergers even five years later.
A research group led by Nanae Domoto, a graduate student at the Graduate School of Science at Tohoku University and a research fellow at the Japan Society for the Promotion of Science (JSPS), has systematically studied the properties of all heavy elements to decode the spectra from neutron star mergers.
They used this to look at the spectra of kilonovae from GW 170817, which are strong emissions brought on by the radioactive decay of newly formed nuclei that are ejected during the merger. The scientists discovered that the rare elements lanthanum and cerium can replicate the near-infrared spectral patterns seen in 2017 based on comparisons of intricate kilonovae spectra simulations conducted by the supercomputer “ATERUI II” at the National Astronomical Observatory of Japan.
Until now, the existence of rare earth elements has only been hypothesized based on the overall evolution of the kilonova’s brightness, but not from the spectral features.
Domoto said, “This is the first direct identification of rare elements in the spectra of neutron star mergers, and it advances our understanding of the origin of elements in the Universe.”
“This study used a simple model of ejected material. Looking ahead, we want to factor in multi-dimensional structures to grasp a bigger picture of what happens when stars collide.”
- Nanae Domoto, Masaomi Tanaka, Daiji Kato, Kyohei Kawaguchi, Kenta Hotokezaka, Shinya Wanajo. Lanthanide Features in Near-infrared Spectra of Kilonovae. The Astrophysical Journal, 2022; 939 (1): 8 DOI: 10.3847/1538-4357/ac8c36