Enhanced production of Fe in massive stars.

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 Fe (iron) and Al (aluminum), offer unique signs of active nucleosynthesis in our galaxy. There is a long-standing discrepancy between the observed Fe/Al ratio by γ-ray telescopes and predictions from supernova models. This discrepancy has been attributed to uncertainties in the nuclear reaction networks producing Fe, and one reaction in particular, the neutron-capture on Fe. Here we present experimental results that provide a strong constraint on this reaction. We use these results to show that the production of Fe in massive stars is higher than previously thought, further increasing the discrepancy between observed and predicted Fe/Al ratios. The persisting discrepancy can therefore not be attributed to nuclear uncertainties, and points to issues in massive-star models.