Gamma rays

electromagnetic radiation from the nuclei of atoms (similar to X rays but with a shorter wave length)

Gamma rays or gamma-ray (denoted as γ) are forms of electromagnetic radiation (EMR) or light emissions of a specific frequency produced from sub-atomic particle interaction, such as electron-positron annihilation and radioactive decay; most are generated from nuclear reactions occurring within the interstellar medium of space. Gamma rays are generally characterized as electromagnetic radiation, having the highest frequency and energy, and also the shortest wavelength, within the electromagnetic spectrum, i.e. high energy photons. Due to their high energy content, they are able to cause serious damage when absorbed by living cells.
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Gamma rays Short wavelength, high energy electromagnetic radiation emitted by radioactive substances. [more]Gamma rays - Community and Resources

electromagnetic radiation with a wavelength of <10 picometers.

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.