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 star. 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.
Read more about Accretion Disc: Manifestations, Accretion Disc Physics, Analytic Models of Sub-Eddington Accretion Discs (thin Discs, ADAFs), Analytic Models of Super-Eddington Accretion Discs (slim Discs, Polish Doughnuts)
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