A cycle of nuclear reactions in which an electron is absorbed by a nucleus and is subsequently re-emitted as a beta particle (a fast electron) with the generation of a neutrino–antineutrino pair. The process makes no change to the composition of the nucleus, but removes energy from it in the form of the neutrino and antineutrino. While insignificant in ordinary stars, it is important at very high densities and temperatures such as those which give rise to supernovae. The process is named after the Urca Casino in Rio de Janeiro, where it was said that money disappeared as rapidly as energy from the stars.
Subjects: Astronomy and Astrophysics.