B Black Holes & Light: Questions from an Average Joe

[Shabumi]

Hi everyone, been reading this site for a while, and this question has been stuck in my head for 3 days and i can't shake it, so i figured I'd step out of the shadows and ask. There are some follow up questions that came on the same train of thought too.
Can light pass by a Black Hole and get close enough to get caught in an orbit around the BH and not get sucked in? If so wouldn't there be a halo of light particles surrounding the BH? Like an atmosphere of light, or rainbow rings due to the different wavelengths stratifying, or perhaps a "lazer wall" due to concentrations of light getting greater over time.
Also, if light passes close enough to a BH to be slowed but not caught by it, after the light escapes the gravity of the BH would it return to the speed of light or would you have "slow light" traveling the universe?
Please keep in mind that I am just an average Joe, and not a physicist in any way so please forgive me if I ask something you would consider stupid. I am not sure what dificulty level to use, so I put it under high school difficulty due to my lack of knowledge base.

 

[PeterDonis]

Can light pass by a Black Hole and get close enough to get caught in an orbit around the BH and not get sucked in?

Technically it can, but the conditions that would be required are so precise that it is extremely unlikely, so the quantity of light that would be captured this way by a black hole will be very small.

if light passes close enough to a BH to be slowed but not caught by it, after the light escapes the gravity of the BH

If the light is caught in orbit around the BH, it never escapes the hole's gravity; it stays in orbit.

would it return to the speed of light

Light always travels at the speed of light. Light that gets caught in an orbit around a BH does not slow down; it just responds to the curvature of spacetime around the BH, which puts it into a trajectory that is an orbit around the hole.

 

[Dale]

If the light is caught in orbit around the BH, it never escapes the hole's gravity; it stays in orbit.

I believe that the photon sphere is unstable. So any perturbation should let it leave orbit.

 

[Shabumi]

Light always travels at the speed of light. Light that gets caught in an orbit around a BH does not slow down; it just responds to the curvature of spacetime around the BH, which puts it into a trajectory that is an orbit around the hole.

Does that mean that light only has 2 options when encountering a black hole? To get captured, either in orbit or sucked in, or to get slingshotted? What if there were a theoretical photon moving directly opposite the gravity from a BH just outside of the capture zone, but still close enough to be effected by the BH gravity, would it still be going the speed of light, or would the BH slow it down like swimming against moving water

 

[PeterDonis]

I believe that the photon sphere is unstable.

Yes, the photon orbits are unstable against small perturbations. Which makes the quantity of light we should expect to find in them in a real black hole even smaller.

 

[PeterDonis]

Does that mean that light only has 2 options when encountering a black hole?

Yes.

What if there were a theoretical photon moving directly opposite the gravity from a BH just outside of the capture zone, but still close enough to be effected by the BH gravity, would it still be going the speed of light, or would the BH slow it down

As I said, light always moves at the speed of light. Light moving away from a BH will be redshifted by the hole's gravity as it goes to increasingly higher altitudes. (Note that this is not limited to a black hole, any gravitating mass causes gravitational redshift; the Pound-Rebka experiment measured it for the Earth.)

 

[Shabumi]

Thank you for your time

 

[Halc]

What if there were a theoretical photon moving directly opposite the gravity from a BH

Then it came from further in, not from outside. Perhaps it was emitted by the accretion material heating up as it gains kinetic energy.

just outside of the capture zone, but still close enough to be effected by the BH gravity

The gravity extends indefinitely, so there's no boundary to that. The photon-sphere (the orbital radius) is 3/2 the Schwarzschild radius, at least for a Schwarzschild black hole. It is very improbable for a photon to be in this orbit since no trajectory from outside can put one there. It has to be emitted at exactly that radius and in exactly the correct direction, and even then it is unstable, so it won't stay there.

would it still be going the speed of light, or would the BH slow it down like swimming against moving water

As other posters have pointed out, light always moves locally at light speed. Relative to a more distant reference, it slows down due to the dilation from the different gravitational potential.