What Are Gamma Rays? What we call "light" is actually just a tiny fraction of the broad range of radiation on the electromagnetic radiation spectrum. The entire span stretches from very-low-energy radio waves through microwaves, infrared light, visible light, ultraviolet light, X rays, and finally to very-high-energy gamma rays. The processes producing photons (single particles of electromagnetic radiation) of each type of radiation differ, as do their energy, but all of the different forms of radiation are still just part of the electromagnetic spectrum's family. The only real difference between a gamma-ray photon and a visible-light photon is the energy. Gamma rays can have over a billion times the energy of the type of light visible to our eyes. They are produced by the hottest and most energetic objects in the universe, such as neutron stars and pulsars, supernova explosions, and regions around black holes. On Earth, gamma rays are generated by nuclear explosions, lightning, and the less dramatic activity of radioactive decay.