Pion production and decay animation. A proton travelling to the speed of light strikes a slower-moving proton. The protons survive the collision, but their interaction creates an unstable particle — a pion — with only 14 percent of the proton's mass. In 10 millionths of a billionth of a second, the pion decays into a pair of gamma-ray photons.
Inverse Compton scattering animation. An electron travelling at close the the speed of light has a head-on collision with a lower-energy photon (from radio to ultraviolet). The photon picks up energy from the electron and becomes a gamma ray.