ABSTRACT
This chapter focuses on some of the effects of the weak interaction in relation to the development of stars. In the course of the development, the weak interaction has several crucial effects. These include the initiation of the gravitational collapse of the centre of a massive star triggering a supernova explosion, the neutronisation of the core material (formation of a neutron star), and lastly the formation of heavy elements above iron via the so called r-process at the final stage of the supernova explosion. During the collapse to a neutron star or to a black hole, observation of the neutrino emission provides the only possibility for direct diagnosis of the events in the interior of the star. Neutrinos carry away most of the energy released in the collapse. The deleptonisation of the core plays a critical role during the collapse and for the eventual explosion.
