Relativistic plasmas may result when two particle beams collide at speeds comparable to the speed of light, and in the cores of supernovae. Plasmas hot enough for particles other than electrons to be relativistic are even more rare, since other particles are more massive and thus require more energy to accelerate to a significant fraction of the speed of light. (About 10% of protons would have γ γ > 2 at a temperature of 481 MeV - 5.6 TK.) Still higher energies are necessary to achieve a quark–gluon plasma.