Hidden Processes in the Center of the Sun Uncovered


Researchers from RWTH Aachen University and Forschungszentrum Jülich publish their findings on the first experimental evidence of fusion processes in heavy stars in the journal Nature.


The scientists involved in the so-called Borexino collaboration have for the first time proven the existence of the CNO fusion cycle in nature by detecting solar neutrinos that originated from this process. They have now published their findings in the renowned scientific journal Nature.

At its core, the sun is a gigantic fusion reactor. Inside, at a temperature of around 15 million degrees, hydrogen nuclei continuously fuse together to form the element helium. In the process, they emit different types of radiation and particles. Some of these are neutrinos. Billions of them pass through every square centimeter on earth every second. This property of being able to pass through materials undisturbed makes them ideal probes for gaining a closer glimpse inside the solar fusion furnace: They provide direct, uncompromised information about the conditions in the center of the sun.

The instrument that enabled this measurement is the Borexino Observatory, where data on neutrinos from the sun have been gathered since 2007. The facility is located in the world’s largest underground laboratory, the Laboratori Nazionali del Gran Sasso, beneath a 1,400-meter-thick layer of dolomitic rock at the Gran Sasso mountain range near Rome, Italy.

“Proof of the CNO neutrinos represents a significant milestone,” explains Professor Livia Ludhova from RWTH’s Department of Experimental Physics 3 B and Head of the Neutrino Group at the Nuclear Physics Institute at Forschungszentrum Jülich. She is one of the two current scientific coordinators of the Borexino collaboration. “This proof paves the way for us to better understand the composition of the sun’s core, particularly its metallicity.” This term, commonly used in astrophysics to refer to the abundance of “heavy” chemical elements in stars, is one of the most important unanswered questions in solar physics today. “The Borexino detector has once again played a pioneering role in research into the sun, unlocking the deepest secrets of the processes that keep our star alive,” underlines Ludhova.

Forschungszentrum Jülich press release