Short-lived ²⁴⁴ Pu points to compact binary mergers as sites for heavy r-process nucleosynthesis

The origin of heavy elements produced through rapid neutron capture ('r-process') by seed nuclei is one of the current nucleosynthesis mysteries ^1-3 . Core collapse supernovae (cc-SNe; ref. 4) and compact binary mergers are considered as possible sites ^5-7 . The first produces small amounts of material at a high event rate whereas the latter produces large amounts in rare events. Radioactive elements with the right lifetime can break the degeneracy between high-rate/low-yield and low-rate/high-yield scenarios. Among radioactive elements, most interesting is ²⁴⁴ Pu (half-life of 81 million years), for which both the current accumulation of live ²⁴⁴ Pu particles accreted via interstellar particles in the Earth's deep-sea floor ⁸ and the Early Solar System (ESS) abundances have been measured ⁹ . Interestingly, the estimated ²⁴⁴ Pu abundance in the current interstellar medium inferred from deep-sea measurements is significantly lower than that corresponding to the ESS measurements. Here we show that both the current and ESS abundances of ²⁴⁴ Pu are naturally explained within the low-rate/high-yield scenario. The inferred event rate remarkably agrees with compact binary merger rates estimated from Galactic neutron star binaries ¹⁰ and from short gamma-ray bursts ¹¹ . Furthermore, the ejected mass of r-process elements per event agrees with both theoretica ^112-14 and observational ^15-17 macronova/kilonova estimates.