 In larger stars , fusion continues until the iron core has grown so large ( more than 1 @.@ 4 M ☉ ) that it can no longer support its own mass . This core will suddenly collapse as its electrons are driven into its protons , forming neutrons , neutrinos , and gamma rays in a burst of electron capture and <unk> beta decay . The <unk> formed by this sudden collapse causes the rest of the star to explode in a supernova . <unk> become so bright that they may briefly <unk> the star 's entire home galaxy . When they occur within the Milky Way , supernovae have historically been observed by naked @-@ eye observers as " new stars " where none seemingly existed before . 
