The international team of about 100 researchers, including scholars from the JU Institute of Physics that conduct the BOREXINO experiment in the underground laboratory in Gran Sasso (Italy), have announced that they have finally determined why large stars are shining. Their discovery was published in the latest issue of Nature.
For the first time, scientists have been able to register unique neutrinos that are direct markers of energy production in the CNO fusion cycle in the Sun. The cycle is the major source of energy for stars larger than the Sun, and has not been previously detected in any star.
For most of a star’s life, which lasts as much as billions of years, they burn hydrogen in their core, leaving helium as residue. In the case of stars such as the Sun or smaller, the burning of hydrogen happens mainly in the ‘proton-proton’ cycle, which features only hydrogen and helium. There are many stars that are larger and hotter than our Sun. Therefore, according to predictions made as far back as 1930s, the second CNO cycle should be the dominant source of energy. In the CNO cycle, carbon, nitrogen and oxygen are the catalysts in the process of burning hydrogen.
The lightest elementary particles, neutrinos, produced in these cycles in the Sun’s core, possess unique spectres that allow physicists to differentiate them from one another. The fact that the BOREXINO team has managed to register CNO neutrinos in our closest star proves that this type of cycle is present there. A stream of neutrinos emitted by the CNO cycle, responsible for around 1% of the Sun’s energy, is much weaker than a ‘proton-proton’ stream. Therefore, it was necessary to first eliminate any background signal. In this way, researchers have confirmed their prediction about the mechanisms governing the stars.
This breakthrough, achieved through long and arduous experimentation, is a fundamental success in the area of astrophysics and elementary particles.
The following JU scientists are participants of the BOREXINO experiment and co-authors of the paper published in Nature: Dr Anna Jany, Dr Marcin Misiaszek, Dr hab. Grzegorz Zuzel, Prof. UJ, and Prof. Marcin Wójcik.