I b ▁and ▁I c ▁super nov ae ▁are ▁a ▁type ▁of ▁core - collapse ▁super n ova ▁for ▁a ▁massive ▁star ▁that ▁has ▁shed ▁its ▁outer ▁en velope ▁of ▁hydro gen ▁and ▁( for ▁Type   I c ) ▁hel ium . ▁As ▁a ▁result , ▁they ▁appear ▁to ▁be ▁lack ing ▁in ▁these ▁elements . ▁ ▁Form ation ▁ ▁Stars ▁far ▁more ▁massive ▁than ▁the ▁sun ▁evol ve ▁in ▁more ▁complex ▁ways . ▁In ▁the ▁core ▁of ▁the ▁star , ▁hydro gen ▁is ▁f used ▁into ▁hel ium , ▁re le asing ▁thermal ▁energy ▁that ▁he ats ▁the ▁sun ' s ▁core ▁and ▁provides ▁out ward ▁pressure ▁that ▁supports ▁the ▁sun ' s ▁layers ▁against ▁collapse ▁in ▁a ▁process ▁known ▁as ▁stell ar ▁or ▁hydro static ▁equilibrium . ▁The ▁hel ium ▁produced ▁in ▁the ▁core ▁accum ul ates ▁there ▁since ▁temper atures ▁in ▁the ▁core ▁are ▁not ▁yet ▁high ▁enough ▁to ▁cause ▁it ▁to ▁f use . ▁Event ually , ▁as ▁the ▁hydro gen ▁at ▁the ▁core ▁is ▁exha usted , ▁fusion ▁starts ▁to ▁slow ▁down , ▁and ▁gravity ▁causes ▁the ▁core ▁to ▁contract . ▁This ▁contra ction ▁ra ises ▁the ▁temperature ▁high ▁enough ▁to ▁initi ate ▁a ▁shorter ▁phase ▁of ▁hel ium ▁fusion , ▁which ▁accounts ▁for ▁less ▁than ▁ 1 0 % ▁of ▁the ▁star ' s ▁total ▁lifetime . ▁In ▁stars ▁with ▁fewer ▁than ▁eight ▁solar ▁masses , ▁the ▁carbon ▁produced ▁by ▁hel ium ▁fusion ▁does ▁not ▁f use , ▁and ▁the ▁star ▁gradually ▁co ols ▁to ▁become