Inhomogeneous Enrichment of Radioactive Nuclei in the Galaxy: Deposition of Live ⁵³Mn, ⁶⁰Fe, ¹⁸²Hf, and ²⁴⁴Pu into Deep-sea Archives. Surfing the Wave?

Abstract

While modeling the galactic chemical evolution (GCE) of stable elements provides insights to the formation history of the Galaxy and the relative contributions of nucleosynthesis sites, modeling the evolution of short-lived radioisotopes (SLRs) can provide supplementary timing information on recent nucleosynthesis. To study the evolution of SLRs, we need to understand their spatial distribution. Using a three-dimensional GCE model, we investigated the evolution of four SLRs: 53Mn, 60Fe, 182Hf, and 244Pu with the aim of explaining detections of recent (within the last ≈1–20 Myr) deposition of live 53Mn, 60Fe, and 244Pu of extrasolar origin into deep-sea reservoirs. We find that core-collapse supernovae are the dominant propagation mechanism of SLRs in the Galaxy. This results in the simultaneous arrival of these four SLRs on Earth, although they could have been produced in different astrophysical sites, which can explain why live extrasolar 53Mn, 60Fe, and 244Pu are found within the same, or similar, layers of deep-sea sediments. We predict that 182Hf should also be found in such sediments at similar depths.

Did a Kilonova Set Off in Our Galactic Backyard 3.5 Myr ago?

“…It must be noticed how BNS mergers (and, more in general, events in which r-process nucleosynthesis occurs) are expected to be rare (Hotokezaka et al 2015;Abbott et al 2023), making their nearby occurrence in the recent past an exceptional event. Additionally, our analysis does not rule out the single supernova origin or the two-step model discussed in previous works, e.g., Wallner et al (2021), Wang et al (2021Wang et al ( , 2023, and Wehmeyer et al (2023). The identification of other relevant isotopic ratios could be the key to discriminating between the different scenarios, as suggested in Wang et al (2021Wang et al ( , 2023.…”

“…The observation of r-process abundance patterns traceable to single events has the potential to shed light on their production site. The detection of live (i.e., undecayed) radioactive isotopes in sediments is powerful in this respect, since it features a nontrivial temporal dependence from their decay profiles (Ellis et al 1996;Wehmeyer et al 2023). There is a common consensus that the 60 Fe (mean lifetime: t Fe 60 ; 3.8Myr) observed in terrestrial and lunar samples points to one or more explosive events happening 10 Myr ago (Mya) not far from the Earth (120 pc).…”

Deep-Sea and Lunar Radioisotopes from Nearby Astrophysical Explosions

“…On scales greater than the Local Bubble, effects of inhomogeneity, mixing, and stochasticity continue to play important roles (162,163). Our larger Galactic environment thus sets the context for the Local Bubble's formation and for possible enrichment by prior events that is modeled in the two-step scenario mentioned above.…”

Could a Kilonova Kill: A Threat Assessment

“…As yet, the time resolution of the 244 Pu signals is insufficient to tell if they are coincident with or independent from the 60 Fe pulses. However, the presence of 244 Pu is evidence for a recent nearby r-process event (Wang et al 2021(Wang et al , 2023Wehmeyer et al 2023), which could be due either to a kilonova (KN) explosion prior to the formation of the Local Bubble, or production by one or more exceptional SNe within the Local Bubble. If the event was a KN, the measured 244 Pu abundance suggests a distance of ∼300 pc (Wang et al 2021).…”