First, the neutrino flux and explosion of a star, and then everything else
Unusually bright events in the universe are the supernovae stars. They are the consequence of sharp gravitational compression of stars at the end of their evolution, and their date can not be predicted with any precision, although neutrino astronomy still allows to learn about the supernova in a few hours before the arrival of electromagnetic waves from the supernova. For an year, hundreds of supernova flashes are registered, and in our galaxy they occur about three times a century. Supernovae of one of their varieties, formed of white dwarfs, give almost identical maximum intensity of the flash. This allows us to quite accurately estimate the distance to a star using its visible brightness, which makes it possible to calculate the acceleration of the universe’s expansion.