I would premit that I am just an enthusiast, so don't expect a good background or a deep mathematical knowledge about the topic. I just read an article about how light is reflected by a black hole (https://www.sciencealert.com/we-now-have-precise-maths-to-describe-how-black-holes-reflect-the-universe/amp). That let me think because, as far as I can understand that imply that the geometrical place where gravitational pull is "just strong enough" to "capture" light has to be a sphere (or geoid if the black hole rotate). What is hard to grasp for me is how perfect that sphere should be in reality (mathematical place doesn't not exist in real world).In other words I am asking if that topic was studied and which is the trending hipotesys about real thickness and smoothness of event horizon (intended as the region of space in which gravitational pull is just strong enough to capture the light, but not too strong).
In general relativity the thickness is zero. In quantum gravity the thickness has a Planck unit thickness which is very thin.
On this sphere, or better, just outside it, Hawing radiation emerges. To avoid the information paradox some theorists have proposed a firewall to exist on the horizon.
Seen from us it is like all matter ends up frozen on the horizon, in a zero volume shell. In a falling frame all matter falls through. There is no horizon at all in this frame.
The Schwarzschild surface is a purely mathematical surface. On this surface light will not fall into the hole nor escape. For us it looks frozen on this sphere. For a falling observer the light on the surface (if tangentially moving) will circle the hole forever (in the classical picture). Untill the horizon gets smaller by vaporizing (Hawking radiation). The photons will be set free in that case.
So. All light that moves close to the horizon can circle it for a small distance and move away again. It can go 180 degrees round the hole. Reflection! Once photons are only 0.00000000000000....1 meter over the horizon they are lost forever only to reappear again as Hawing photons, which are entangled with all particles that fall in (well, if they are entangled is still the question and this is one of the reasons a firewall is thought to exist).