This breakthrough not only confirms hypotheses dating back to the 1930s but also ranks among the greatest discoveries in physics of the new millennium.
“This is a significant breakthrough in the field of solar physics and astrophysics,” says researcher Gioacchino Ranucci from the National Institute for Nuclear Physics (INFN) in Italy, one of the experts involved in the project since its inception in 1990.
The scientists utilized the highly sensitive particle counting machine called Borexino at the Gran Sasso National Laboratory of the INFN in central Italy. This underground research facility, located deep beneath the Apennine Mountains, approximately 105 km northeast of Rome, is the largest of its kind in the world.
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Photo: NASA
The team of experts’ discovery marks the culmination of the solar neutrino research project, revealing for the first time the crucial nuclear reaction that most stars, including our Sun, employ to synthesize hydrogen into helium. Nearly all stars, including our Sun, release immense amounts of energy through the process of converting hydrogen into helium.
Hydrogen, the most abundant element, serves as the primary source of energy in the universe. In the case of the Sun, 99% of its energy is generated through the proton-proton fusion reaction, which produces beryllium, lithium, and boron before decaying into helium. However, most stars in the universe are larger than our Sun. For instance, the red giant star Betelgeuse is about 20 times larger and has a diameter 700 times greater than that of the Sun.
These larger stars are also hotter, meaning they are constantly fueled by the CNO cycle (carbon-nitrogen-oxygen fusion reaction). The CNO cycle is also the dominant source of energy in the universe but is challenging to detect in cooler stars like our Sun, where it accounts for only about 1% of the energy released by the Sun.
The Borexino particle detector has long been searching for evidence of neutrinos generated in the nuclear fusion process at the core of the Sun. However, neutrinos are extremely difficult to detect. Every second, billions of neutrinos from the Sun pass through the Borexino particle detector, but it can only capture about 7 neutrinos per day from the CNO cycle.
After a prolonged period of monitoring, the researchers have finally found the first evidence confirming the occurrence of the CNO cycle in the Sun and other stars in the universe. According to long-standing hypotheses, neutrinos emitted from the Big Bang event that gave birth to the universe may play a role in dark matter, a form of mysterious matter surrounding stars and galaxies, constituting about 25% of their mass.