Discovery of supernova relic neutrinos——the next milestone of neutrino astronomy

Understanding supernovae plays a crucial role in the study of the evolution of stars, the generation of elements, neutron stars, black holes, and gravitational waves. There are many measures to observe supernovae explosions, and the extremely weak interaction between neutrinos and matter provides a unique perspective, especially for the study of the physical mechanism inside supernovae. It is very difficult to detect neutrinos from the supernovae in the Milky Way because of their low burst rate of less than three per century. In contrast, the total supernova burst rate of neighboring galaxies far from the Milky Way exceeds one every decade. Experiments have begun that will be able to detect neutrinos from all galaxies including those near our Milky Way since the Big Bang of the universe; these constitute the isotropic background flux of neutrinos and are referred to as supernova relic neutrinos. If these are discovered, it would be a milestone in neutrino astronomy. This article will review the detection, challenges, and hopes of current and future relevant experiments.