ive ▁and ▁un stable ▁stages ▁during ▁the ▁later ▁pre – main ▁sequence ▁phase ▁of ▁the ▁Hay ashi ▁contra ction ▁may ▁be ▁one ▁of ▁the ▁main ▁sources ▁of ▁energy ▁for ▁T ▁Ta uri ▁stars . ▁Rap id ▁rotation ▁tends ▁to ▁improve ▁mixing ▁and ▁increase ▁the ▁transport ▁of ▁l ith ium ▁into ▁deeper ▁layers ▁where ▁it ▁is ▁destroyed . ▁T ▁Ta uri ▁stars ▁generally ▁increase ▁their ▁rotation ▁rates ▁as ▁they ▁age , ▁through ▁contra ction ▁and ▁spin - up , ▁as ▁they ▁con serve ▁angular ▁momentum . ▁This ▁causes ▁an ▁increased ▁rate ▁of ▁l ith ium ▁loss ▁with ▁age . ▁Lith ium ▁burning ▁will ▁also ▁increase ▁with ▁higher ▁temper atures ▁and ▁mass , ▁and ▁will ▁last ▁for ▁at ▁most ▁a ▁little ▁over ▁ 1 0 0 ▁million ▁years . ▁▁ ▁The ▁P - P ▁chain ▁for ▁Lith ium ▁burning ▁is ▁as ▁follows ▁ ▁: {| ▁border =" 0 " ▁| - ▁style =" height : 2 em ;" ▁|   || +   ||   || →   || ||   || ▁| - ▁style =" height : 2 em ;" ▁|   || +   ||   || →   ||   || +   ▁| - ▁style =" height : 2 em ;" ▁|   || +   ||   || →   ||   ||   || ( unst able ) ▁| - ▁style =" height : 2 em ;" ▁|   ||   ||   || →   || 2    || + ▁energy ▁| } ▁ ▁It ▁will ▁not ▁occur