New research has shed light on how strontium, a metal found in items like glow-in-the-dark paint and fireworks, is formed inside stars. Scientists have long used theoretical models to explain how elements heavier than iron are created in stars, but some observations of very old stars didn’t match these models. A team led by Caley Harris, a former graduate student at the Facility for Rare Isotope Beams (FRIB), has taken a significant step toward resolving this discrepancy. Their study, published in Communications Physics, focused on a key nuclear reaction involving krypton-88, a rare isotope. By measuring the rate at which krypton-88 captures neutrons, the team reduced the uncertainty in this process from a factor of eight to about three. This improvement helped refine models of how strontium is produced in stars, bringing predictions closer to what astronomers observe in the cosmos. The team used the SuN detector, a specialized instrument installed at the Argonne Tandem Linac Accelerator System (ATLAS), to produce krypton-89—krypton-88 with an extra neutron—and measured the gamma-ray emissions that followed. These emissions provided clues about the neutron-capture rate of krypton-88. The study involved scientists from 12 institutions across the U.S., Canada, and Europe, highlighting the collaborative nature of the work. The SuN detector’s ability to capture these emissions allowed the researchers to reconstruct the nuclear reaction pathway and estimate the neutron-capture rate with greater accuracy. In astrophysics, strontium is particularly interesting because it appears in the chemical signatures of very old stars. These stars, formed in the early universe, contain clues about the processes that created heavier elements. Understanding strontium’s formation helps scientists piece together the history of element creation in the cosmos. Traditionally, scientists have relied on three main processes—r-process, s-process, and p-process—to explain the formation of heavy elements. However, some observations of ancient stars showed an abundance of strontium that didn’t align with these models. This led to the proposal of the i-process, a less understood mechanism that operates under conditions between the s- and r-processes. The i-process was thought to be a potential explanation, but previous models predicted too little strontium. This gap pointed to missing or uncertain nuclear data, especially the neutron-capture rate of krypton-88. The new study shows that this rate is consistently lower than previously predicted, which, when applied to i-process models, results in higher predicted strontium production. This better matches the observed amounts in old stars. The researchers suggest that future studies should focus on astrophysical factors, such as neutron density and the timing of nuclear reactions in stars, to further refine the models. Their findings underscore the importance of laboratory experiments on rare isotopes in bridging the gap between nuclear physics and astronomical observations.