Like all stars, our sun combines hydrogen into powerful elements. Nuclear fusion not only causes stars to glow, but is also the primary source of the chemical elements that make up the world around us.
Much of our understanding of stellar fusion is based on theoretical models of atomic nuclei, but we have another source for our nearest star: Neutrinos Created at the core of the sun.
When atomic nuclei undergo fusion, they produce not only high energy gamma rays but also neutrinos. Gamma rays have been heating the interior of the Sun for thousands of years, and neutrinos travel out of the Sun at the speed of light.
Solar neutrinos were first discovered in the 1960s, but it was difficult to learn much about them except when they were ejected from the Sun. It has been proven that nuclear fusion occurs in the sun, but not the type of fusion.
Theoretically, the main form of fusion in the Sun must be a combination of protons producing helium from hydrogen. Known as the PP-chain, it is the easiest reaction to create stars.
For larger stars with hotter and denser cores, there is a stronger reaction known as the CNO-cycle .The main source of energy. This reaction produces helium using hydrogen in the reaction cycle with carbon, nitrogen, and oxygen.
The CNO cycle is one of the most abundant of these three elements in the universe (except hydrogen and helium).
Neutrino detectors have become much more efficient in the last decade. Modern detectors can detect not only the energy of a neutrino, but also its taste.
We know that solar neutrinos discovered from early experiments are not from ordinary PP-chain neutrinos, but from secondary reactions such as boron decay, which produce high-energy neutrinos that are easy to detect.
Then a team in 2014 Discovered low energy neutrinos directly produced by the PP-chain. Their observations confirmed that proton-proton fusion produces 99 percent of the Sun’s energy.
Although the PP-chain dominates the conjunction in the Sun, our star CNO cycle is large enough to occur. This should be about 1 percent of the sun’s energy.
But CNO neutrinos are rare and difficult to detect. But recently a team successfully observed them.
The biggest challenge in detecting CNO neutrinos is that their signal is buried within the terrestrial neutrino sound. Nuclear fusion does not occur naturally on Earth, but radioactive decay from Earth rocks can cause events in neutrino detectors similar to CNO neutrino detections.
So the team created an innovative analytics process that filters the neutrino signal from false positives. Their study confirms that CNO synthesis occurs on our Sun at unpredictable levels.
The CNO cycle plays a small role in our Sun, but it is also the center for the life and evolution of more giant stars.
This work will help us to understand the cycle of the big stars and to better understand the origin of the heavier elements that make life possible on Earth.
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