**O-Stars** O stars have inner convective zones, and the core within an O star is very far into the star, very hot, very dense. --> O stars do different types of nuclear burning, mainly CNO cycle, which must happen at much higher temperature. temperature scaling of this is ***$T^{17}$, meaning that the rate of fusion changes as a function to the 17th power with every change in temperature. As a result, O-type stars fuse incredibly quickly, leading to forced convection as there is so much energy pouring out from the core.