Rare Particles from the Sun Discovered Under a Mountain in Italy

The particles called CNO cycle neutrinos prove that the Sun has two methods for hydrogen fusion.
Loukia Papadopoulos
Inside view of the Borexino detectorBorexino

For the first time ever, physicists have detected rare particles called CNO cycle neutrinos on Earth. Initially, the particles were assumed to only exist on the Sun.

CNO cycle neutrinos are subatomic particles produced by the sun's Carbon-Nitrogen-Oxygen cycle. For this experiment, it seems that the neutrinos traveled from the Sun to the detector that was buried deep underneath a mountain in Italy.

The experiment, called Borexino, brings us closer to understanding what happens on our Sun. Borexino wasn't an easy feat, described by its conductors as a real "daunting task."

Rare Particles from the Sun Discovered Under a Mountain in Italy
View of the internal of the Borexino Stainless Steel Sphere, Source: Borexino

"In general, Solar Neutrinos can be caught only with highly sensitive detectors, capable of suppressing most sources of background signals. To achieve the required sensitivity, the Borexino experiment was built with an onion-like design, characterized by layers of increasing radiopurity while moving from the periphery to the center," wrote the statement concerning the discovery.


The Borexino detector is made of a tank 60 feet (18 meters) tall that contains 280 tons (254 metric tons) of scintillating liquid. This is a liquid that emits a light when electrons inside it interact with a neutrino.

It is also buried deep underground and cocooned in a water tank. This was necessary because, without severe shielding, other signals would drown out the rare signals coming from the CNO neutrinos.

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Rare Particles from the Sun Discovered Under a Mountain in Italy
PMTs installed on the Borexino Stainless Steele Sphere, Source: Borexino

The impressive device was able to achieve results that may close a chapter of physics that begun in the 1930s. Back in 1938, Bethe and von Weizsäcker independently hypothesized that hydrogen fusion in the Sun might be catalyzed by the heavy nuclei carbon, nitrogen, and oxygen.

They speculated that this second mechanism of hydrogen burning into helium complemented the Sun's dominant energy-generating process. However, the two hypothesized engines powering the Sun and the stars could only be proved via a direct experimental confirmation of detecting the rare and ghostly neutrinos that the Borexino experiment finally achieved.

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