What Physical Processes Generate Gamma Rays?

The origin of gamma rays is intimately tied the physics of elementary particles, such as protons, neutrons, and electrons. Some of the known physical processes that can produce gamma rays are:
Synchrotron Radiation Synchrotron Radiation is produced when charged particles such as electrons spiral at speeds approaching the speed of light in the presence of a magnetic field. Supernovae and supernova remnants produce a lot of synchrotron radiation.

Matter-Antimatter Annihilation When a particle of matter (such as an electron) collides with its anti-matter twin (in this case, the positron), they annihilate each other. This Matter-Antimatter Annihilation produces a pair of gamma rays at a specific wavelength, depending on the mass of the annihilating particles.

Nuclear Decay Nuclear Decay, also called radioactivity, occurs when the nucleus of an unstable element spontaneously transforms into a new element, emitting an alpha or beta particle and a gamma ray. The composition of the decaying nucleus determines the wavelength of the gamma ray, so that the decaying elements in an astronomical object can be identified by the gamma rays they produce.

Inverse Compton Scattering Inverse Compton Scattering occurs when a photon and an energetic charged particle (such as an electron) scatter off of each other. The kinetic energy of the particle can be transferred to the photon, increasing its energy and decreasing its wavelength into the gamma ray regime.

Bremsstrahlung When a speeding electron interacts with a positively charged nucleus it is deflected by the electric field of the nucleus. The electron is decelerated as its path changes, and the energy lost due to the deceleration emerges as a photon, called Bremsstrahlung (German for "braking radiation"). If the electron is moving fast enough, the emergent photon can be a gamma ray.

High Speed Collisions High Speed Collisions of protons or any other atomic nuclei can result in the production of a variety of exotic subatomic particles, whose rapid decays can produce gamma ray photons.

Fusion The Fusion of two atomic nuclei leads to heavier atomic nuclei, as well as the emission of gamma rays.

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