# Diamond ring around black hole

I know that light takes longer to travel in a denser material, like diamond and I know that black holes also attract light. I was wandering what would happen if you would make a ring out of diamond, spin it up at high speed and put it around a black hole. If I got this right the speed of light inside a diamond object is half of light in vacuum. My question is, could you make a prison for the light outside the black hole? Would the light that enters the ring just go down to the black hole, instead of continuing it's path like it would do if there was no ring? Would the ring be like an extension to the black object that the black hole is or something else would happen?

Edit: Well, I guess most of the light would be reflected off so I think that my question now is a little silly but this is mainly what I had envisioned. Mostly a ring that would spin with enough speed that it doesn't get sucked into the black hole and it stays close enough and it has enough thickness so that objects that go at half of the speed of light near it will be directed back into the black hole.

The yellow lines are light rays. The blue parts are the diamond. On the left is a 'top' view of the black hole with it's ring and on the right there is a small portion of the ring where the doted line is the path that light would take without gravity involved.

• You want to be careful when you say "black holes attract light" because that sounds like it has several incorrect implications. Black holes are simply bodies which have exceptionally strong gravitational fields(due to high mass), and hence have terminal velocities greater than $c$.
– user191954
May 25, 2018 at 16:07
• Can you add a diagram? It's somewhat difficult to envision what exactly you're thinking about.
– user191954
May 25, 2018 at 16:09
• I've added a diagram. May 25, 2018 at 18:08

## 1 Answer

It's 40% of the speed in vacuum. The chemical bonds in the diamond wouldn't stand up to the gravitational tidal forces anywhere near close enough for gravity to be affecting light.

Black holes generally have an accretion disc, and streams of polar ejecta because of their huge electromagnetic fields. So around the 'middle', hot matter approaching relativistic speeds, and top & bottom powerful radiation beams. Quite hostile all round.

What are you intending with this question? Why are you asking it? I would guess you would be interested to know light has been slowed to zero in matter, and this may have important applications in optical computing https://www.newscientist.com/article/dn4474-light-frozen-in-its-tracks/

• Well, I was just curious. I was thinking that I can hear of something new and interesting by asking the question. And it seems I was right. May 25, 2018 at 13:22