An Etymological Dictionary of Astronomy and Astrophysics

The smallest → circular orbit in which a particle can stably orbit a → black hole according to → general relativity without the risk of falling past the → event horizon. In other words, the ISCO is the inner edge of the → accretion disk around a black hole. Therefore, characteristics of accretion disks depend on ISCO. The radius of ISCO is calculated to be three times the → Schwarzschild radius (3 R_Sch). ISCO is closer to event horizon for rotating black hole.

See also: → inner; → stable; → circular; → orbit.