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Scientists make major breakthrough in finding out why the Sun shines

Scientists have detected neutrinos formed during a largely mysterious process in the Sun, in what they are hailing as a major breakthrough.

The discovery could help reveal the structure of our Sun and the elements within its core. But it could also allow us to better understand other phenomena throughout the universe, such as supernovae or the insides of distant stars.

The detection was made using the Borexino Collaboration, a vast particle physics experiment located in Italy and worked on by researchers from around the world. It aims to better understand the processes powering the Sun, as well as those in other stars.

An expert who was not involved in the research said that the new results “blast past a milestone in neutrino physics”.

“Measurements of these neutrinos have the potential to resolveuncertainties about the composition of thesolar core, and offer crucial insights into the formation of heavy stars," wrote Gabriel D Orebi Gann from the University of California, Berkeley, in an article accompanying the publication of the research in Nature.

“The Borexino Collaboration’s tremendous accomplishment moves us closer to a complete understanding of our Sun, and of the formation of massive stars, and is likely to define the goal in this field for years to come.”

Stars shine from the nuclear fusion of hydrogen into helium. That can happen in two ways: what is called the proton–proton or pp chain, which involves only hydrogen and helium, or the carbon–nitrogen–oxygen or CNO cycle, where the fusion is catalysed by carbon, nitrogen and oxygen.

In our own Sun, and other stars of a similar size, the pp chain accounts for some 99 per cent of the energy. Researchers have studied it extensively since the early 1970s, and the Borexino experiment has helped contribute to a comprehensive understanding of the processes that govern it.

But the CNO cycle – which represents a tiny but important minority of the energy production – has proven almost entirely evasive. The small number of neutrinos that come from that mechanism mean that they are difficult to separate from background signals.

Now researchers say they have detected neutrinos coming from that process, however. Because the Borexino detector is sensitive and highly attuned so that it can block out background noise – as a result of recent breakthroughs that allow for the detector to stop the detector being contaminated – it was able to specifically pick up those neutrinos, which until now have remained mysterious.

The two nylon vessels in the core of Borexino filled with water during the initial operation of the detector

It is the first ever time that researchers have been able to pick up those neutrinos – or direct evidence for the CNO cycle in any form at all. It is the first time that humanity has seen evidence of the mechanism that converts hydrogen into helium throughout the universe.

It also confirms theories about that cycle, including the fact that it accounts for only one per cent of the Sun’s energy.

Though that is a small proportion of the Sun’s power, the discovery could lead to large breakthroughs in the understanding of stars, the researchers say. The measurements can be used to understand how much carbon, nitrogen and oxygen might be found in stars such as our Sun, and how it might be structured.

What’s more, other, heavier stars are thought to rely on the CNO cycle much more than our own Sun, where that process is the dominant way of producing energy. The new findings could help show whether that is true and by what degree, allowing us to understand how other stars are powered too.

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