astrophysical neutrino

The term astrophysical neutrino naturally refers to a neutrino other than those from Earth (from radioactive decay, human activities such as nuclear reactors, and reactions on Earth from cosmic rays), and typically also is meant to exclude the two well-known sources that produce the majority of neutrinos reaching Earth: the cosmic neutrino background, and solar neutrinos. Both these excluded populations have limited kinetic energy, and the term astrophysical neutrino often is used to mean higher energy than solar, though this may well exclude some neutrinos from distant sources that happen to have lower energy. To use a detected neutrino in the study of astrophysical phenomena that also can be studied by other methods (multi-messenger astronomy), knowing its trajectory well enough to identify the source by other means is critical, and the term astrophysical neutrino may sometimes be meant to imply something of the trajectory has been determined (which also might distinguish such low-energy neutrinos from solar). Astrophysical neutrino research progress has been limited in the past because handling their rarity and high energy, as well as determining their trajectory, all demand large, expensive detectors.

Some other neutrino terms regarding their sources that are also generally associated with more specific energy intervals: extragalactic neutrino, cosmological neutrino, GZK neutrino (aka cosmogenic neutrino), the latter presumed to be a product of the GZK effect.