# Radius of the accretion disc?

1. Jun 7, 2009

### tiny-tim

What is the inner radius of an accretion disc?

Is it simply the radius of the smallest possible orbit of a massive particle (the marginally stable radius), 6M ?

2. Jun 8, 2009

### stevebd1

Hi tiny-tim

In most cases, the inner edge of the accretion disk is considered to coincide with the marginally stable which is 6M for a static black hole, reducing to 1M for a maximal Kerr black hole where a/M=1, though there seems to be some debate that the properties of the accretion disk itself can have an effect on this-