Speaker
Description
The diffuse $\gamma$-ray emission from short-lived radioactive $^{26}\text{Al}$ and $^{60}\text{Fe}$ provides a direct probe of ongoing nucleosynthesis in the Galaxy. However, theoretical models have long struggled to reproduce the observed $^{60}\text{Fe}/^{26}\text{Al}$ 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 $\beta^-$ decay rate of $^{59}\text{Fe}$ on the nucleosynthesis of these isotopes. We compute a grid of nonrotating massive star models (14–80 $M_\odot$) 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 $^{60}\text{Fe}$ by approximately 0.28 dex ($\sim 47\%$) compared to models using LMP theoretical rates, while leaving the $^{26}\text{Al}$ yields virtually unchanged. This reduction is primarily driven by the enhanced $\beta^-$ decay during convective carbon-shell burning. Integrating these yields over a standard Salpeter initial mass function (IMF), we predict a Galactic flux ratio of $\sim 0.18$, which is in excellent agreement with the observed value of $0.184 \pm 0.042$. Furthermore, this ratio exhibits a weak dependence on the IMF slope. Our results indicate that the updated nuclear physics input significantly alleviates the longstanding $^{60}\text{Fe}$ overproduction problem, bringing theoretical predictions into much closer alignment with current Galactic observations.
| Category | Theory |
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