 Innermost stable circular orbit

The innermost stable circular orbit is the smallest stable circular timelike orbit around a black hole. Its radius and orbital energy depend on black-hole spin and on whether the orbit is prograde or retrograde.

The innermost stable circular orbit (ISCO) is a concept from general relativity that pertains to the orbits of objects around compact astrophysical objects, such as black holes or neutron stars. The ISCO represents the smallest orbit in which a test particle (like a small mass moving under gravitational influence) can stably orbit a massive body without spiraling into it due to gravitational or tidal forces. Here are key points about the ISCO: 1. **Stable vs.