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Astronomy milestone: Researchers first discovered neutrinos from the Sun’s so-called CNO cycle, a fusion reaction predicted 82 years ago. Protons do not dissolve directly, but bind to helium through the catalysis of heavy elements such as carbon, nitrogen and oxygen. The first direct evidence of this CNO cycle has now been obtained from neutrinos, a major turning point for stellar research.
Our sun receives its energy Nuclear fusion – Hydrogen is converted into helium. About 99 percent of these fusion reactions occur in our star through direct fusion of protons. But in early 1938 the physicists Hans Bethe and Carl Friedrich von Weissecker suggested that there should be a second connection. These so-called CNO cycles, in which carbon, nitrogen and oxygen react with the fusion reaction.
Neutrinos like fusion boats
In the sun, this CNO fusion accounts for only one percent of all fusion processes. But in the case of the larger stars it is the dominant reaction pattern. “The CNO cycle is therefore the primary means of converting hydrogen to helium in the universe,” explains Gioachino Ranucci and his colleagues from the Borexino collaboration. But despite its importance, this merging path has yet to be demonstrated directly in a star.
Now things have changed: 82 years after the theoretical prediction of the CNO cycle, the researchers of the Borexino collaboration have now proved it experimentally. They did this with the help of solar neutrinos – nearly massless particles released as a byproduct of fusion reactions. Hundreds of billions of such neutrinos go unnoticed in our body every second. The fusion reaction of such a particle can be read from its energy with others.
The glow of light in the underground laboratory
The problem, however, is that CNO fusion neutrinos are relatively rare and have low energy up to a maximum of 1,700 kV. This makes them easier to use. Radiation decay reactions to confuse the released neutrinos. To detect CNO neutrinos, it is necessary to have diagnoses that are maximally protected from such mutations.
One of these discoveries is the borexin in the Gran Sasso laboratory. The underground neutrino detector is protected from the outside world by a thick rock, a steel shell and several reservoirs of liquid. In the center of the structure is a detector tank filled with 278 tons of organic liquid. When a neutrino collides with one of the liquid atoms it contains, a small incandescent light is generated, which is registered by the photosynthesizers.
In order to search for solar CNO neutrinos, the researchers evaluated the detection data from July 2016 to February 2020 and filtered them in detail and statistically.
720 million CNO neutrinos per second and square centimeters
They discovered what they were actually looking for: of the many neutrinos from other sources, they were the first to identify particles from the CNO fusion. Their discovery recorded an average of 7.2 CNO neutrinos and 100 tons of fluid per day. Considering that most of these CNO neutrinos go unnoticed, their actual size is enormous: “It could turn into 720 million CNO neutrinos, which flow into the earth every second and every centimeter,” the Boraxino scientists explain.
This is the first time that the CNO cycle in the Sun has been directly detected by the neutrinos formed during this fusion path. They confirm that such a CNO merger occurs in the sun, along with Bethe and Van Weiss’s theory of 82 years ago. At the same time, the measured values correspond to the samples, so that this melting path is one percent of the total solar fusion reactions.
“Milestone in neutrino physics”
Gianfolo Bellini, co-author of the University of Milan, said: “This gives us the first, surprising proof of how stars produce a heavier luminosity than the Sun. At the same time, these measurements open a way to determine more closely the content of heavier elements in the Sun and other stars. It affects the size of the CNO connection.
Gabriel Orebi Gunn, physicist at the University of California, Berkeley, writes :, 2020; Thoi: doi: 10.1038 / s41586-020-2934-0)
Quell: Borexino Collaboration
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