▁it ▁becomes ▁ener get ically ▁favor able ▁for ▁electrons ▁and ▁pro tons ▁to ▁merge ▁via ▁inverse ▁beta ▁decay , ▁producing ▁neut rons ▁and ▁elementary ▁particles ▁called ▁neut r inos . ▁Because ▁neut r inos ▁rarely ▁interact ▁with ▁normal ▁matter , ▁they ▁can ▁escape ▁from ▁the ▁core , ▁carrying ▁away ▁energy ▁and ▁further ▁acceler ating ▁the ▁collapse , ▁which ▁proceed s ▁over ▁a ▁times c ale ▁of ▁mill iseconds . ▁As ▁the ▁core ▁det aches ▁from ▁the ▁outer ▁layers ▁of ▁the ▁star , ▁some ▁of ▁these ▁neut r inos ▁are ▁absor bed ▁by ▁the ▁star ' s ▁outer ▁layers , ▁beginning ▁the ▁super n ova ▁explos ion . ▁ ▁For ▁Type   II ▁super nov ae , ▁the ▁collapse ▁is ▁eventually ▁halt ed ▁by ▁short - range ▁rep uls ive ▁neut ron - neut ron ▁interactions , ▁medi ated ▁by ▁the ▁strong ▁force , ▁as ▁well ▁as ▁by ▁deg ener acy ▁pressure ▁of ▁neut rons , ▁at ▁a ▁density ▁compar able ▁to ▁that ▁of ▁an ▁atomic ▁nucle us . ▁When ▁the ▁collapse ▁stops , ▁the ▁inf alling ▁matter ▁reb ounds , ▁producing ▁a ▁shock ▁wave ▁that ▁propag ates ▁out ward . ▁The ▁energy ▁from ▁this ▁shock ▁dis soci ates ▁heavy ▁elements ▁within ▁the ▁core . ▁This ▁reduces ▁the ▁energy ▁of ▁the ▁shock , ▁which ▁can ▁st all ▁the ▁explos ion ▁within ▁the ▁outer ▁core . ▁ ▁The ▁core ▁collapse ▁phase ▁is ▁so ▁dense ▁and ▁ener get ic ▁that ▁only ▁neut r inos ▁are ▁able ▁to ▁escape . ▁As ▁the ▁pro tons ▁and ▁electrons ▁combine