<P> The CNO cycle ( for carbon -- nitrogen -- oxygen ) is one of the two known sets of fusion reactions by which stars convert hydrogen to helium , the other being the proton -- proton chain reaction . Unlike the latter , the CNO cycle is a catalytic cycle . It is dominant in stars that are more than 1.3 times as massive as the Sun . </P>
the cno cycle dominates in which types of stars
more than 1.3 times as massive as the Sun