▁are ▁power ed ▁by ▁gravit ational ▁energy ▁released ▁as ▁the ▁stars ▁contract , ▁while ▁moving ▁towards ▁the ▁main ▁sequence , ▁which ▁they ▁reach ▁after ▁about ▁ 1 0 0 ▁million ▁years . ▁They ▁typically ▁rotate ▁with ▁a ▁period ▁between ▁one ▁and ▁twelve ▁days , ▁compared ▁to ▁a ▁month ▁for ▁the ▁Sun , ▁and ▁are ▁very ▁active ▁and ▁variable . ▁ ▁There ▁is ▁evidence ▁of ▁large ▁areas ▁of ▁star spot ▁coverage , ▁and ▁they ▁have ▁inten se ▁and ▁variable ▁X - ray ▁and ▁radio ▁em issions ▁( appro xim ately ▁ 1 0 0 0 ▁times ▁that ▁of ▁the ▁Sun ). ▁Many ▁have ▁extremely ▁powerful ▁stell ar ▁wind s ; ▁some ▁e ject ▁gas ▁in ▁high - vel ocity ▁b ip olar ▁j ets . ▁Another ▁source ▁of ▁bright ness ▁vari ability ▁are ▁cl umps ▁( pro top lan ets ▁and ▁plan etes im als ) ▁in ▁the ▁disk ▁surrounding ▁T ▁Ta uri ▁stars . ▁ ▁Their ▁spect ra ▁show ▁a ▁higher ▁l ith ium ▁abund ance ▁than ▁the ▁Sun ▁and ▁other ▁main - sequence ▁stars ▁because ▁l ith ium ▁is ▁destroyed ▁at ▁temper atures ▁above ▁ 2 , 5 0 0 , 0 0 0 ▁K . ▁From ▁a ▁study ▁of ▁l ith ium ▁abund ances ▁in ▁ 5 3 ▁T ▁Ta uri ▁stars , ▁it ▁has ▁been ▁found ▁that ▁l ith ium ▁de ple tion ▁var ies ▁strongly ▁with ▁size , ▁suggesting ▁that ▁" l ith ium ▁burning " ▁by ▁the ▁P - P ▁chain ▁during ▁the ▁last ▁highly ▁con ve ct