Rare Earth Elements Are Created During Neutron Star Mergers, Study Confirms

Before now, scientists thought that rare earth elements existed based on how bright a kilonova became over time, not on their spectral properties. “This is the first direct identification of rare elements in the spectrum of neutron star mergers and advances our understanding of the origin of elements in the Universe,” explained Dotomo. “This study used a simple model of expelled material. Going forward, we want to take multidimensional structures into account to understand a bigger picture of what happens when stars collide,” added Dotomo. You can see the study for yourself in the journal. The Astrophysical Journal.

Study Summary: “The observations of GW170817/AT2017gfo have provided us with evidence that binary neutron star mergers are sites of r-process nucleosynthesis. However, the signatures observed in the spectra of GW170817/AT2017gfo have not been fully decoded, especially in the near infrared (NIR). In this paper, we investigate kilonova spectra across the entire wavelength range with the goal of elemental identification. We systematically calculate the strength of linked transitions by building a list of hybrid lines that is accurate for large and full strong transitions. for weak transitions. We found that elements on the left side of the periodic table, such as Ca, Sr, Y, Zr, Ba, La, and Ce, tend to produce prominent absorption lines in the spectra. This is because such elements they have a small number of valence electrons and low energy levels, resulting in strong transitions. By performing self-consistent radiative transfer simulations for the entire ejecta, we found that tLa iii and Ce iii appear in the NIR spectra, which can explain the absorption characteristics at λ ∼ 12000–14000 Å in the spectra of GW170817/AT2017gfo. The mass fractions of La and Ce are estimated to be >2 × 10−6 and ∼(1–100) × 10−5, respectively. A Th actinide element can also be a source of absorption since the atomic structure is analogous to that of Ce. However, we show that Th iii features are less prominent in the spectra due to the denser energy levels of the actinides. compared to those of the lanthanides.