The early universe and clustering of the relic neutrinos

The astronomical consequences of a neutrino mass on the order of 10 eV are assessed. According to big bang cosmology, the neutrino blackbody radiation was excited in the early universe and, in the case of a neutrino mass of less than 1 MeV, would remain until now in the form of relic neutrinos without undergoing pair annihilation. These neutrinos may contribute to the average density of the universe, and may also be the main source of gravity in astronomical objects such as galactic clusters. While it is understood that neutrino-bound systems with masses on the order of galactic clusters are formed through a growth of the primordial density fluctuation in the relic neutrino distribution, there is as yet no explanation of how the protocluster fragments form individual galaxies and the massive halos of neutrinos around them. If the neutrino mass is larger than 10 eV, the missing mass in those galactic systems could be explained by the rest mass of the neutrino