▁of ▁a ▁few ▁months . ▁As ▁iron ▁and ▁nick el ▁have ▁the ▁highest ▁binding ▁energy ▁per ▁nucle on ▁of ▁all ▁the ▁elements , ▁energy ▁cannot ▁be ▁produced ▁at ▁the ▁core ▁by ▁fusion , ▁and ▁a ▁nick el - ir on ▁core ▁grows . ▁This ▁core ▁is ▁under ▁huge ▁gravit ational ▁pressure . ▁As ▁there ▁is ▁no ▁fusion ▁to ▁further ▁raise ▁the ▁star ' s ▁temperature ▁to ▁support ▁it ▁against ▁collapse , ▁it ▁is ▁supported ▁only ▁by ▁deg ener acy ▁pressure ▁of ▁electrons . ▁In ▁this ▁state , ▁matter ▁is ▁so ▁dense ▁that ▁further ▁comp action ▁would ▁require ▁electrons ▁to ▁occup y ▁the ▁same ▁energy ▁states . ▁However , ▁this ▁is ▁forb idden ▁for ▁identical ▁ferm ion ▁particles , ▁such ▁as ▁the ▁electron ▁– ▁a ▁phenomen on ▁called ▁the ▁Paul i ▁ex clusion ▁principle . ▁ ▁When ▁the ▁core ' s ▁mass ▁exceed s ▁the ▁Ch andr ase k har ▁limit ▁of ▁about ▁, ▁deg ener acy ▁pressure ▁can ▁no ▁longer ▁support ▁it , ▁and ▁cat ast roph ic ▁collapse ▁ens ues . ▁The ▁outer ▁part ▁of ▁the ▁core ▁reaches ▁veloc ities ▁of ▁up ▁to ▁ ▁( 2 3 % ▁of ▁the ▁speed ▁of ▁light ) ▁as ▁it ▁col laps es ▁toward ▁the ▁center ▁of ▁the ▁star . ▁The ▁rapidly ▁shr inking ▁core ▁he ats ▁up , ▁producing ▁high - energy ▁g amma ▁ray s ▁that ▁de compose ▁iron ▁nuc lei ▁into ▁hel ium ▁nuc lei ▁and ▁free ▁neut rons ▁via ▁phot od is integration . ▁As ▁the ▁core ' s ▁density ▁increases ,