A high energy form of electromagnetic radiation. The wavelength of gamma rays is typically less than 10-12 metres. They differ from X-rays in that they originate in the nucleus of atoms. A gamma ray is a photon, i.e. a discrete packet of many waves. Like all electromagnetic radiation it travels at the speed of light and when thought of as a particle is a boson with intrinsic angular momentum (spin) 1. It carries a quantum of energy (E=hf, where h is Planck's constant and f the frequency of the wave) and linear momentum and hence exerts radiation pressure. There are no gamma rays in the nucleus, any more than there are any photons in an atom, they are created at the instant of emission.
Some very hot (> 106
K) neutron stars emit radiant energy, not in the visible region, but in the form of gamma rays (possibly bremsstrahlung ). One such example is Pulsar 1055-52.