. ▁ ▁In ▁fact , ▁some ▁theoretical ▁models ▁incorpor ate ▁a ▁hyd rod ynam ical ▁inst ability ▁in ▁the ▁st alled ▁shock ▁known ▁as ▁the ▁" Stand ing ▁Acc ret ion ▁Sho ck ▁Inst ability " ▁( S AS I ). ▁This ▁inst ability ▁comes ▁about ▁as ▁a ▁consequence ▁of ▁non - s pher ical ▁perturb ations ▁oscill ating ▁the ▁st alled ▁shock ▁thereby ▁de form ing ▁it . ▁The ▁S AS I ▁is ▁often ▁used ▁in ▁tan dem ▁with ▁neut r ino ▁theories ▁in ▁computer ▁simulations ▁for ▁re - ener g izing ▁the ▁st alled ▁shock . ▁ ▁Computer ▁models ▁have ▁been ▁very ▁successful ▁at ▁calculating ▁the ▁behavior ▁of ▁Type   II ▁super nov ae ▁when ▁the ▁shock ▁has ▁been ▁formed . ▁By ▁ign oring ▁the ▁first ▁second ▁of ▁the ▁explos ion , ▁and ▁assuming ▁that ▁an ▁explos ion ▁is ▁started , ▁ast ro phys ic ists ▁have ▁been ▁able ▁to ▁make ▁detailed ▁predictions ▁about ▁the ▁elements ▁produced ▁by ▁the ▁super n ova ▁and ▁of ▁the ▁expected ▁light ▁curve ▁from ▁the ▁super n ova . ▁ ▁Light ▁curves ▁for ▁Type   II - L ▁and ▁Type   II - P ▁super nov ae ▁ ▁When ▁the ▁spectrum ▁of ▁a ▁Type   II ▁super n ova ▁is ▁exam ined , ▁it ▁normally ▁displays ▁Bal mer ▁absor ption ▁lines ▁– ▁reduced ▁flux ▁at ▁the ▁characteristic ▁frequencies ▁where ▁hydro gen ▁atoms ▁abs orb ▁energy . ▁The ▁presence ▁of ▁these ▁lines ▁is ▁used ▁to ▁distinguish ▁this ▁category ▁of ▁super n ova ▁from ▁a ▁Type   I