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Like all stars, our sun is powered by combining hydrogen into heavier components. Atomic fusion is not only the brightness of the stars, but also the primary source of the chemical elements that make up the world around us.
Much of our understanding of stellar fusion comes from theoretical models of atoms, but as for our closest star, we have another source: the neutrinos formed in the center of the sun.
Whenever atoms undergo fusion, they produce not only high-energy gamma rays but neutrinos as well. As gamma rays heat the Sun’s interior for thousands of years, neutrinos whiz across the Sun at the speed of light.
Solar neutrinos were first discovered in the 1960s, but it’s hard to learn much about them other than the fact that they were ejected from the sun. This showed that nuclear fusion occurs in the sun, but not the type of fusion.
Theoretically, the dominant form of fusion in the Sun would be the combination of protons that produce helium from hydrogen. This so-called PP chain is an easy reaction to form stars.
For larger stars with hotter and denser nuclei, the most powerful reactive energy, called the CNO rotation, is the dominant source. This reaction uses hydrogen in the cycle of reactions with carbon, nitrogen and oxygen to produce helium.
The CNO cycle is one of the three components of the universe (with the exception of hydrogen and helium).
The CNO cycle begins at higher temperatures. (RJ Hall)
Neutrino detectors have multiplied effectively over the past decade. Modern inventors are able to discover not only the energy of a neutrino but also its taste.
The solar neutrinos detected by the first experiments do not derive from common PP-chain neutrinos, but from secondary reactions such as the decay of boron, which produce easily identifiable high-energy neutrinos.
Then, in 2014, a team of low-energy neutrinos produced directly from the PP chain was detected. Their observations confirmed that 99% of the solar energy is generated by proton-proton fusion.
Energy levels of various solar neutrinos. (Heron / Brown University)
While the PP chain dominates the convergence of the Sun, our star is large enough that the CNO cycle occurs at low levels. This should be the reason for the 1% more energy produced by the sun.
But CNO neutrinos are rare and difficult to detect. But recently a team noticed them successfully.
One of the biggest challenges in detecting CNO neutrinos is burying their signal surface in neutrino noise. Atomic fusion does not occur naturally on Earth, but low levels of radioactive decay from Earth’s rocks can trigger events in a neutrino detector similar to CNO neutrino detections.
The team then developed a sophisticated analytical process that filters the neutrino signal from false positives. Their study confirms that CNO fusion occurs at predicted levels within our Sun.
The CNO cycle plays a small role in our Sun, but is also central to the life and evolution of more massive stars.
This work will help us understand the rotation of large stars and better understand the origin of the heavier elements that make life on Earth possible.
This article was originally published today by the Universe. Read the original article.
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