Accretion disc

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Artist's conception of a binary star system with one black hole and one main sequence star.

An accretion disc (or accretion disk) is a structure formed by diffuse material in orbital motion around a central body. The central body is typically either a young star, a protostar, a white dwarf, a neutron star, or a black hole. Instabilities within the disc redistribute angular momentum, causing material in the disc to spiral inward towards the central body. Gravitational energy released in that process is transformed into heat and emitted at the disk surface in form 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.

[change] Other websites

• Professor John F. Hawley homepage
• Nonradiative Black Hole Accretion
• Accretion Discs on Scholarpedia
• Magnetic fields snare black holes' food - New Scientist

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