# Relativistic particle

Massive particles are relativistic when their kinetic energy is comparable to or greater than the energy ${\displaystyle mc^{2}}$ corresponding to their rest mass. In other words, a massive particle is relativistic when its total mass-energy (rest mass + kinetic energy) is at least twice its rest mass. This condition implies that the particle's speed is close to the speed of light. According to the Lorentz factor formula, this requires the particle to move at 86.6025% or more of the speed of light. Such relativistic particles are generated in particle accelerators,[1] as well as naturally occurring in cosmic radiation.[2] In astrophysics, jets of relativistic plasma are produced by the centers of active galaxies and quasars.