Where do neutrinos come from?
They can be produced in many ways: they are created in solar fusion, in radioactive decays, in fission reactions (for instance, in nuclear reactors), in particle collisions (for instance, when cosmic rays strike the atmosphere or in accelerators), in supernova explosions (more on that later), and in exotic astrophysical objects. There are also “relic” neutrinos everywhere, left over from the Big Bang. We’re basically awash in a vast sea of neutrinos, all just sliding right through us at nearly the speed of light.
