Astrophysics (Index)About

innermost stable circular orbit

(border of region surrounding a BH in which orbits are unstable)

The term innermost stable circular orbit (ISCO) is used for black holes and neutron stars: an orbit at the distance from the center of the object (the ISCO-radius) immediately beyond that for which general-relativity effects make such an orbit unstable. The rotation of the host object affects this distance, but for the simple case of no rotation:

rISCO = 6GM/c² = 3RS

(black holes,orbits)
Further reading: