129I and 247Cm in Meteorites Constrain the Last Astrophysical Source of Solar r-process Elements

TL;DR

This study uses meteoritic data of radioactive isotopes 129I and 247Cm to identify neutron star mergers as the likely last source of solar r-process elements, highlighting the importance of specific astrophysical conditions.

Contribution

It provides new constraints on the last astrophysical source of r-process elements by analyzing meteoritic isotope ratios and comparing them with nucleosynthesis models.

Findings

Moderately neutron-rich conditions fit meteoritic data best.

Radioactive isotope ratio preserved over 15.6 Myr half-lives.

Uncertain nuclear physics data affect confidence in results.

Abstract

The composition of the early Solar System can be inferred from meteorites. Many elements heavier than iron were formed by the rapid neutron-capture process (r process), but the astrophysical sources where this occurred remain poorly understood. We demonstrate that the near-identical half-lives ($\simeq$ 15.6 Myr) of the radioactive r-process nuclei 129I and 247Cm preserve their ratio, irrespective of the time between production and incorporation into the Solar System. We constrain the last r-process source by comparing the measured meteoritic 129I / 247Cm = 438 $\pm$ 184 to nucleosynthesis calculations based on neutron star merger and magneto-rotational supernova simulations. Moderately neutron-rich conditions, often found in merger disk ejecta simulations, are most consistent with the meteoritic value. Uncertain nuclear physics data limit our confidence in this conclusion.