Short-lived radioisotopes in meteorites from Galactic-scale correlated star formation

TL;DR

This study uses high-resolution simulations of the Milky Way to show that short-lived radioisotopes in the early Solar System likely originated from large-scale galactic star formation processes, not from local supernova triggers.

Contribution

It provides a novel galactic-scale simulation approach demonstrating that SLRs are distributed through correlated star formation, challenging previous local confinement or triggering hypotheses.

Findings

SLR abundance ratios in the Solar System are typical.

SLRs originate from galactic-scale star formation, not local confinement.

Star formation is correlated across the galaxy, influencing SLR distribution.

Abstract

Meteoritic evidence shows that the Solar system at birth contained significant quantities of short-lived radioisotopes (SLRs) such as 60Fe and 26Al (with half-lives of 2.6 and 0.7 Myr respectively) produced in supernova explosions and in the Wolf-Rayet winds that precede them. Proposed explanations for the high SLR abundance include formation of the Sun in a supernova-triggered collapse or in a giant molecular cloud (GMC) that was massive enough to survive multiple supernovae (SNe) and confine their ejecta. However, the former scenario is possible only if the Sun is a rare outlier among massive stars, while the latter appears to be inconsistent with the observation that 26Al is distributed with a scale height significantly larger than GMCs. In this paper, we present a high-resolution chemo-hydrodynamical simulation of the entire Milky-Way Galaxy, including stochastic star formation, HII regions, SNe, and element injection, that allows us to measure for the distribution of 60Fe/56Fe and 26Al/27Al ratios over all stars in the Galaxy. We show that the Solar System's abundance ratios are well within the normal range, but that SLRs originate neither from triggering nor from confinement in long-lived clouds as previously conjectured. Instead, we find that SLRs are abundant in newborn stars because star formation is correlated on galactic scales, so that ejecta preferentially enrich atomic gas that will subsequently be accreted onto existing GMCs or will form new ones. Thus new generations of stars preferentially form in patches of the Galaxy contaminated by previous generations of stellar winds and supernovae.