Enhanced production of 60Fe in massive stars

TL;DR

This paper presents experimental data that suggests massive stars produce more 60Fe than previously estimated, highlighting a persistent discrepancy between observed and predicted isotope ratios that likely stems from stellar modeling issues.

Contribution

The study provides new experimental constraints on neutron-capture reactions, revealing higher 60Fe production in massive stars and emphasizing the need to refine stellar models.

Findings

Higher 60Fe production in massive stars than previously thought

Persistent discrepancy between observed and predicted 60Fe/26Al ratios

Nuclear uncertainties are unlikely to resolve the ratio discrepancy

Abstract

Massive stars are a major source of chemical elements in the cosmos, ejecting freshly produced nuclei through winds and core-collapse supernova explosions into the interstellar medium. Among the material ejected, long lived radioisotopes, such as 60Fe (iron) and 26Al (aluminum), offer unique signs of active nucleosynthesis in our galaxy. There is a long-standing discrepancy between the observed 60Fe/26Al ratio by {\gamma}-ray telescopes and predictions from supernova models. This discrepancy has been attributed to uncertainties in the nuclear reaction networks producing 60Fe, and one reaction in particular, the neutron-capture on 59Fe. Here we present experimental results that provide a strong constraint on this reaction. We use these results to show that the production of 60Fe in massive stars is higher than previously thought, further increasing the discrepancy between observed and predicted 60Fe/26Al ratios. The persisting discrepancy can therefore not be attributed to nuclear uncertainties, and points to issues in massive-star models.