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In research published Wednesday in the journal Nature, scientists reported that they have made the first detection of near-ethereal particles called neutrinos that can be traced to the carbon-nitrogen-oxygen fusion, known as the CNO cycle, inside the sun.
It is a fundamental discovery that confirms the theoretical predictions of the 1930s, and has been hailed as one of the greatest discoveries in physics of the new millennium.
“It’s really a breakthrough for solar and stellar physics,” said Gioacchino Ranucci of the Italian National Institute of Nuclear Physics (INFN), one of the researchers on the project since its inception in 1990.
Scientists used the ultra-sensitive Borexino detector at INFN’s Gran Sasso particle physics laboratory in central Italy, the largest underground research center in the world, deep in the Apennines, about 65 miles north-east of Rome.
The detection concludes the Borexino project’s decades of solar neutrino study and reveals for the first time the major nuclear reaction that most stars use to fuse hydrogen into helium.
Almost all stars, including our sun, give off enormous amounts of energy by fusing hydrogen into helium – effectively a way to “burn” hydrogen, the simplest and most abundant element and the main fuel source in the universe. .
In the case of the sun, 99 percent of its energy comes from proton-proton fusion, which can create beryllium, lithium and boron before breaking them down into helium.
But most of the stars in the universe are much larger than our sun – the red giant Betelgeuse, for example, is about 20 times more massive and about 700 times wider.
Large stars are also much hotter, which means they are overwhelmingly fueled by CNO fusion, which fuses hydrogen into helium by means of transformed atomic nuclei in an infinite loop between carbon, nitrogen and oxygen.
The CNO cycle is the dominant energy source in the universe. But it’s hard to spot inside our relatively cool sun, where it only accounts for 1% of its energy.
The giant detector Borexino looks for neutrinos emitted during nuclear fusion in the sun’s core.
Neutrinos barely interact with anything, so they’re ideal for studying nuclear reactions from a distance, but they’re also extremely difficult to detect.
Trillions of neutrinos from the sun pass through the Borexino detector every second, but it only detects dozens of them every day looking for faint flashes of light as they decay in its 300-ton dark water tank.
Ranucci said the Borexino detector spent decades measuring neutrinos from the sun’s main proton-proton chain reaction, but detecting its CNO neutrinos was very difficult: only about seven neutrinos with the revealing energy of the CNO cycle were identified in one day.
The discovery has required making the detector increasingly sensitive over the past five years, he said, protecting it from external sources of radioactivity so that the detector’s inner chamber is the most radiation-free place on Earth.
The result is the only direct sign of CNO merger ever seen anywhere: “This is the first evidence that the CNO cycle is at work in the sun and stars,” Ranucci said.
Gabriel Orebi Gann, a particle physicist at the University of California, Berkeley, called the discovery “an important milestone”.
“This discovery takes us one step closer to understanding the composition of our sun’s core and the formation of heavy stars,” he said.
Orebi Gann is the author of a scientific article in Nature on the new study, but was not involved in the research.
Neutrinos are naturally produced in nuclear reactions and pass through most matter with no effect, so they can be used to probe otherwise unreachable regions of the universe, he said.
For this reason, several neutrino detectors are observing their fleeting presence around the world in the dark, including the IceCube observatory at the South Pole and the Super-Kamiokande detector in Japan.
It is theorized that the Big Bang neutrinos may explain part of the mysterious “dark matter” of the universe: vast invisible halos around stars and galaxies that make up about a quarter of its mass.
Orebi Gann said that an asymmetry between neutrinos and their antiparticles could also explain the apparent deficiency of antimatter in our universe and its dominance over normal matter – in other words, precisely because there is something here, rather than absolutely. nothing.
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