2026/05/28 by Bingyang Tan, 谭炳阳, Wenyu Xin +3
#Nuclear physics research studies #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies
paper · pdf · doi:10.3847/1538-4357/ae74d2
Abstract The diffuse γ -ray emission from short-lived radioactive 26 Al and 60 Fe provides a direct probe of ongoing nucleosynthesis in the Galaxy. However, theoretical models have long struggled to reproduce the observed 60 Fe/ 26 Al flux ratio, typically predicting values significantly higher than the constraints derived from INTEGRAL/SPI observations. In this work, we investigate the impact of the recently measured temperature-dependent stellar β − decay rate of 59 Fe on the nucleosynthesis of these isotopes. We compute a grid of nonrotating massive star models (14–80 M ⊙ ) at solar metallicity using the MESA code, coupled with a rigorous numerical resolution analysis. We find that the updated rate significantly suppresses the net production of 60 Fe by approximately 0.28 dex (∼47%) compared to models using LMP theoretical rates, while leaving the 26 Al yields virtually unchanged. This reduction is primarily driven by the enhanced β − decay during convective carbon-shell burning. Integrating these yields over a standard Salpeter initial mass function (IMF), we predict a Galactic flux ratio of ∼0.18, which is in excellent agreement with the observed value of 0.184 ± 0.042. Furthermore, this ratio exhibits a weak dependence on the IMF slope. Our results indicate that the updated nuclear physics input significantly alleviates the longstanding 60 Fe overproduction problem, bringing theoretical predictions into much closer alignment with current Galactic observations.