Like all stars, our sun is powered by hydrogen combined with heavier components. Atomic fusion is not only the glow 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 when it comes to our closest star, we have another source: Neutrinos formed at the center of the sun.
When atoms fuse, they produce not only high-energy gamma rays but also neutrinos. While gamma rays have warmed the interior of the Sun for thousands of years, neutrinos compress the Sun at the speed of light.
Solar neutrinos were first discovered in the 1960s, but it’s hard to learn much about them apart from the fact that they were ejected from the Sun. This proved that nuclear fusion occurs in the sun, but not of the fusion type.
Theoretically, the dominant form of fusion in the Sun should be the combination of protons that produce helium from hydrogen. This so called PP chain is an easy reaction to form a star.
For larger stars with hotter and denser cores, the strongest reactive energy called the CNO spin is the dominant source. This reaction uses hydrogen in the reaction cycle with carbon, nitrogen and oxygen to produce helium.
The CNO cycle is one of the three components of the universe (except hydrogen and helium).
Neutrino detectors have proliferated in the last decade. Modern inventors can discover not only the energy of a neutrino but also its taste.
Solar neutrinos detected in early experiments are not derived from common PP chain neutrinos, but from secondary reactions such as boron decay that produce easily identifiable high-energy neutrinos.
Later in 2014, a team of low-energy neutrinos produced directly by the PP chain was spotted. Their observations confirmed that 99 percent of solar energy is produced by proton-proton fusion.
While the PP chain dominates the Sun’s convergence, our star is large enough for the CNO cycle to occur at low levels. This must be the reason for the extra 1 percent energy produced by the sun.
However, CNO neutrinos are rare and difficult to detect. Recently, however, a team has successfully noticed them.
One of the biggest challenges in detecting CNO neutrinos is burying the signal surfaces in neutrino noise. Atomic fusion does not occur naturally on Earth, but low levels of radioactive decay from terrestrial rocks can trigger events in a neutrino detector similar to CNO neutrino detections.
The team therefore developed a complex analytical process that filters the neutrino signal from false positives. Their studies confirm that CNO fusion occurs at predicted levels in our Sun.
The CNO cycle plays a minor role in our Sun, but it is also central to the life and evolution of more massive stars.
This work will help us understand the rotation of massive stars and better understand the origin of the heavier elements that made life possible on Earth.
This article was first published today at Universe. To read the original article.