Latin accretion-, accretio, from accrescere
- Date: 1615
- 1 : the process of growth or enlargement by a gradual buildup: as a : increase by external addition or accumulation (as by adhesion of external parts or particles) b : the increase of land by the action of natural forces
- 2 : a product of accretion; especially : an extraneous addition <accretions of grime>
An accretion disc is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a central body. The central body is typically a young star, a protostar, a white dwarf, a neutron star, or a black hole. Gravity causes material in the disc to spiral inward towards the central body. Gravitational forces compress the material causing the emission of electromagnetic radiation. The frequency range of that radiation depends on the central object. Accretion discs of young stars and protostars radiate in the infrared; those around neutron stars and black holes in the x-ray part of the spectrum.