University of Notre Dame researcher Michael Wiescher and collaborators reviewed techniques used to determine nuclear reaction rates in cold stellar environments and shared newer concepts for measuring low-energy nuclear reactions.

Wiescher, a professor in the University of Notre Dame Department of Physics and Astronomy, and collaborators proposed a new concept for predicting the emergence of low-energy resonances because of the effects of quantum mechanics. Their work, Quantum physics of stars appeared in Reviews of Modern Physics. Research in this area may someday be applied to the defense industry and to the development of fusion reactors, alternative power sources that could potentially provide a safe, sustainable resource for producing electricity later this century.

Using theoretical models, researchers predicted the emergence of strong resonances at very low energies. In unusual circumstances, particles can briefly stick together, even if they normally would not. This happens when two different quantum states interact or “couple,” causing a temporary resonance, which is similar to tuning two radios to the same frequency. Scientists can predict when this will happen by understanding how these quantum states influence each other.

Fusion, a process where two atomic nuclei combine to form a heavier nucleus and release excess energy, powers our Sun and all stars. Low-mass stars burn fuel slower and live for billions of years, while high-mass stars burn through their fuel much faster. With few significant measurements of these reactions, it has been difficult to learn exactly how the process works, Wiescher said.

In his paper Wiescher collaborated with several theorists and discussed the quantum effects that may impact reactions. Though experimental advances using deep underground accelerators have improved the understanding of nuclear reactions at low energies, nuclear reactions at stellar burning conditions rely on theoretical extrapolations, which are now considerably improved through the understanding and implementation of the quantum effects in the calculations.

Many examples in the paper pertain to stable beams. However, nuclear reactions far from stability, such as the proton and neutron capture reaction on unstable particles investigated at Michigan State’s Facility for Rare Isoptope Beams are important, Wiescher said. Researchers also reviewed advanced theoretical techniques to extrapolate reaction cross sections into new-threshold regions for nuclei far-off stability.

Scientists need to understand the quantum threshold effects discussed in the review paper in order to reliably model nuclear reaction processes, Wiescher said. This includes not only models for stars but also for low-temperature plasma environments such as controlled magnetic or inertial confinement fusion systems, which operate in similar temperatures. Wiescher described these as similar to “suns for a mere nanosecond.”

In addition to researchers at Notre Dame, collaborators included researchers from East Texas A&M University, Commerce, Texas; Grand Accélérateur National d’Ions Louds, Caen Cedex, France; GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany; Michigan State University, East Lansing, Michigan; Ohio University, Athens, Ohio; Polish Academy of Sciences, Kraków, Poland; TRIUMF, Vancouver, Canada; Universidade de São Paulo, Brazil; Università degli Studi di Enna “Kore,” Enna, Italy; and University of Surrey, Guildford, United Kingdom.

The work was supported in part by funding from the National Science Foundation and the U.S. Department of Energy Office of Science Office of Nuclear Physics.

Originally published by Deanna Csomo Ferrell at science.nd.edu on August 11, 2025.