| Astrophysics (Index) | About |
Solar neutrinos, neutrinos from the Sun, were the first detected from off Earth in the 1960s after well-established models of fusion predicted their existence and practical detection methods were devised. After relic neutrinos (those from very soon after the Big Bang), which are by far the most common neutrinos passing through Earth's neighborhood, solar neutrinos are the next the most common. The bulk of cosmic neutrinos have by far the lowest kinetic energy (KE), with the bulk of solar neutrinos, the next lowest, up to about 400 keV. KE is a clue in determining whether a neutrino is one of these or is from some other astronomical source.
The first neutrino observatories were aimed at detecting solar neutrinos, but some newer ones clearly aim to detect those from other astronomical sources. There are more solar neutrinos to detect, but their low energy makes it a challenge to detect them. The solar neutrino unit (SNU) is a unit devised to relate interactions used in the detection of neutrinos to the rate of neutrinos from the Sun, and reflects the fact that the neutrino interactions that are detected have very low probability.
The solar neutrino problem was an anomaly in the results of detections of solar neutrinos: detections were only a fraction of what theory had predicted. This anomaly provided support to the theories of neutrino oscillation and the Mikheyev-Smirnov-Wolfenstein effect (MSW effect), which explains the anomaly, and eventual observation of the effect's predicted neutrino flavors confirmed the effect to be the cause of the anomaly. The detection of solar neutrinos along with confirmation that they match theory is considered a detailed confirmation that the Sun produces its energy from fusion at the solar core.