Neutron star collisions may forge gold more slowly than expected

Neutron star collisions may produce gold, platinum, and other heavy elements more slowly than previously believed, according to a recent study led by researchers at Technische Universität Darmstadt. The findings, published in Physical Review Letters, suggest that the rapid neutron-capture process, known as the r-process, is influenced more significantly by the mass of atomic nuclei than earlier models had assumed. This discovery could reshape scientists' understanding of how heavy elements are synthesized in the cosmos. The study focused on the r-process, which is responsible for creating approximately half of all elements heavier than iron. This process typically occurs during violent astrophysical events, such as the collision of two neutron stars. During these collisions, atomic nuclei absorb neutrons rapidly, allowing them to form increasingly heavier elements. However, many of the neutron-rich nuclei involved in this process are too unstable to be studied in terrestrial laboratories, forcing scientists to rely heavily on theoretical models. To address this challenge, the research team used a novel computational approach called the Valence-Space In-Medium Similarity Renormalization Group (VS-IMSRG) method. Takayuki Miyagi and Achim Schwenk, working under the guidance of Professor Almudena Arcones, calculated the properties of 70 critical nuclei near the magic neutron number N = 82. This region is vital for producing the second r-process abundance peak, a well-known pattern of heavy element distribution found across the universe. These newly computed nuclear masses were integrated into detailed simulations of nucleosynthesis, modeling scenarios ranging from neutron star mergers to other extreme astrophysical phenomena. The results showed that the calculated masses slowed the progression of material through the r-process more than prior models had predicted. This slowdown causes matter to accumulate for a longer duration in a particular area of the nuclear chart before the creation of even heavier elements can proceed. Jan Kuske, the lead author of the study and a doctoral student in Arcones' group, emphasized that minor variations in nuclear masses can have substantial effects on the predicted abundances of heavy elements in the universe. The study suggests a more pronounced second r-process peak and a noticeable shift in the third peak, offering fresh perspectives on how gold, platinum, and similar elements are formed after neutron star collisions. The implications of this research extend beyond theoretical physics. Many of the nuclei essential to the r-process will likely remain inaccessible even with advanced accelerator facilities planned for the future. Therefore, precise theoretical methods are growing in importance. The study highlights that ab initio nuclear structure calculations have now matured enough to provide direct contributions to understanding astrophysical processes and the cosmic origins of elements. The research underscores the value of integrating experimental data with cutting-edge theoretical models, especially in areas where experimental studies are limited. By doing so, scientists can identify the most promising isotopes for future investigations, guiding both laboratory experiments and observational astronomy efforts. The paper titled “r-Process Nucleosynthesis with Ab Initio Nuclear Masses around the N=82 Shell Closure” was authored by J. Kuske and colleagues and published in Physical Review Letters in 2026. It presents a significant advancement in the field, offering a more accurate framework for predicting the production rates of heavy elements in the universe.