New source of neutrinos from the Sun is seen for the first time by the Borexino collaboration – Technology News, Firstpost

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In a remarkable experiment designed to provide answers to one of the main mysteries about our Sun, physicists have reported finding evidence of a new source of neutrinos that was first discovered.

Neutrinos are small subatomic particles that interact only through weak force and gravity. What makes neutrinos unique (and a complex subject to be studied) is that they are electrically neutral and have a mass so small that it was thought to be zero. The mass of a neutrino is much less than any other known particle that makes up atoms.

Solar neutrinos, or neutrinos from the sun, are all around us and passing us at any moment. Scientists estimated that 100 billion solar neutrinos just pass our thumbnail every second that passes. Neutrons are the products of the main reaction that powers the sun and other stars – nuclear fusion.

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The Sun, captured by NASA's Solar Dynamics Observatory, pointing to "active regions" on its surface, where there are bright spots and illuminated arches, on April 20, 2015. Image credit: NASA / SDO

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Stars are fed most of their lives by nuclear fusion at their core. The main type of nuclear fusion that occurs in the core of a star is protons (charged hydrogen molecules) being converted to helium. That said, depending on the mass of the star itself, this conversion can occur in different ways.

In the nuclei of stars like the Sun, most of the energy produced (99%) comes from a process called proton-proton chain reaction (pp). This process creates helium from the fusion of two protons, releasing a positron and a neutrino in the process. The reaction releases an enormous amount of energy in the form of gamma rays.

However, in our Sun, there is little evidence to explain where the lost energy comes from (the remaining 1%). Physicists theorized that it could be produced in another set of nuclear fusion reactions called CNO chain reactions.

The CNO cycle uses carbon, nitrogen and oxygen as intermediates to finally produce helium, just like in the pp chain. However, there has been no experimental neutrino evidence for this reaction so far.

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In stars much heavier than our Sun, the CNO cycle is the main source of energy.

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Scientists had already detected neutrinos in 1956 and established a firm link with the most prevalent fusion process, the pp chain, in 2001.

But only now, remarkably, have neutrinos from the second set of reactions – the CNO cycle – been detected. Researchers in the Borexino experiment have been working to measure low-energy solar neutrinos – a central feature in the history of absent solar neutrinos – since 2000.

The Borexino team announced its findings on June 23 at the Neutrino 2020 virtual meeting, concluding that the "search (for) CNO neutrinos finally produced the first observation of the signal", in their presentation.

The study still awaits peer review before the announcement is made official.

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