Old Physics wrote:
As I understand it, the circular orbital velocity at a given
radius will be the escape velocity at twice that radius.

That's valid in Newtonian mechanics for an orbit around a fixed
pointlike mass. Newtonian mechanics is inadequate to describe black
holes (and "fixed pointlike mass" is over-idealized...).

How is it
determined that the circular orbit for light is 1.5 times the radius
of event horizen?

By solving the geodesic equation of GR, and looking for circular null
orbits.

Note your statement applies ONLY to a Schwarzschild black
hole, and "radius" is really the Schw. r coordinate, not
really what the word normally means.


If viewed from far away, would the light running in a circle
around a BH appear to be slower than c?

See my previous remarks about the ambiguities inherent in non-local
observations like this.


Tom Roberts