Scientists say there’s new evidence that our sun is experiencing a second entire mode of fusion, indicated by the presence of neutrinos in a very hard-to-find energy range. That means the sun is doubling its output by harmonizing on different wavelengths.
The sun is pretty small for a star, and different sizes of stars have different kinds of fusion reactions at their cores. Universe Today explains: “According to theory, the dominant form of fusion in the Sun should be the fusion of protons that produces helium from hydrogen. Known as the pp-chain, it is the easiest reaction for stars to create. For larger stars with hotter and more dense cores, a more powerful reaction known as the CNO-cycle is the dominant source of energy. This reaction uses hydrogen in a cycle of reactions with carbon, nitrogen, and oxygen to produce helium.”
But detecting the evidence of different kinds of reactions is difficult. Enter neutrinos, which are lightweight, neutral subatomic particles that can pass through matter almost without any evidence. This is because of their physical properties and the fact that they respond to the weak, rather than strong, force of physics in our universe. (In a colloquial sense, the furthest extension of the weak interaction of neutrinos is something like dark matter, which scientists believe is mingling around us all the time without disturbing our matter.)
Because of how neutrino detection technology developed, the way we discovered neutrinos wasn’t in order of abundance, for example. The first neutrinos we were able to find represent an unusual chemical reaction at much higher energy than many other reactions. That makes sense—the highest-energy neutrinos are the most likely to make a blip big enough to appear on something made by people using materials that mostly respond in the strong force realm.
The CNO-cycle mentioned above is, in contrast, one of the most difficult neutrinos to observe. Scientists have known for years that the sun’s energy is mostly a result of pp-chain reaction, but they couldn’t say for sure if it had CNO-cycle processes that are found in way bigger stars. And detecting them is procedurally hard.
Universe Today explains: “One of the biggest challenges with detecting CNO neutrinos is that their signal tends to be buried within terrestrial neutrino noise. Nuclear fusion doesn’t occur naturally on Earth, but low levels of radioactive decay from terrestrial rocks can trigger events in a neutrino detector that are similar to CNO neutrino detections.”
To solve this problem, scientists made a neutrino-noise coin sorter that shakes out the big, heavy quarters, so to speak, leaving behind the finer and less heavy dimes. With their new noise-filtering tool, they have the first sound measurement of the sun’s combination of CNO-cycle as well as pp-chain reactions.
And, the scientists say, this could pave the way to a more sophisticated understanding of how small stars and large stars share common reactions in different quantities as size and circumstances change.