Rotating Black Hole w/ Ring: Spacetime Effects

In summary, the conversation discusses the effects of a rotating black hole and a ring of matter orbiting it at ultra-relativistic speeds. The addition of the ring would enhance the frame-dragging effect of the black hole, potentially leading to the formation of a naked singularity or wormhole. However, there is currently no known solution or numerical simulation for this scenario. The idea of a ring-shaped black hole is deemed impossible and it is suggested to run numbers to better understand the effects of the ring on the black hole.
  • #1
A Puzzlement
7
1
What would spacetime look like near a black hole that was rotating at its extremal speed and had a ring of matter orbiting it at ultra-relativistic speeds (just outside the photon sphere), such that the ring was orbiting in the same direction as the black hole’s rotation?

The ring would add to the frame-dragging effect already present due to the black hole’s own rotation. If the ring was massive enough, could this lead to the event horizon disappearing and the formation of a naked singularity or wormhole?

I was thinking a Kardashev III civilization might be able to build such a ring around its galaxy’s black hole. Maybe we should keep our eyes peeled.
 
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  • #2
A Puzzlement said:
The ring would add to the frame-dragging effect already present due to the black hole’s own rotation.

This is a reasonable heuristic guess, but AFAIK there is no known solution to the Einstein Field Equation that actually describes this. Someone might have done a numerical simulation of it, but I'm not aware of any.

A Puzzlement said:
If the ring was massive enough, could this lead to the event horizon disappearing and the formation of a naked singularity or wormhole?

Again, since we have no known exact solution or numerical simulation, the best we can do is a heuristic guess. My heuristic guess would be no, because of the general rule that you can't take a near-extremal rotating hole and make it extremal or super-extremal; to do that, you would have to increase the hole's spin, but any process that increases the spin of a near-extremal hole increases its mass also, by at least enough to keep it from becoming extremal or super-extremal.
 
  • #3
I wonder such a ultrarelativistic and massive ring becomes a black hole itself.
 
  • #4
Yeah, that’s why I came up with the idea of the orbiting ring as a kind of loophole. Since the ring isn’t technically part of the black hole, the super-extremality problem is avoided.

However, like you mentioned, we need someone to actually find a solution to the equations for this system. Hopefully there’s someone willing to take a stab at it. It seems like an interesting possibility to investigate.

I could imagine sci-fi stories involving such a ring.
 
  • #5
sweet springs said:
I wonder such a ultrarelativistic and massive ring becomes a black hole itself.

A ring-shaped black hole orbiting another black hole? Interesting!
 
  • #6
sweet springs said:
I wonder such a ultrarelativistic and massive ring becomes a black hole itself.

If it did, it would amount to the ring being swallowed by the rotating hole, increasing the rotating hole's size.

A Puzzlement said:
A ring-shaped black hole orbiting another black hole? Interesting!

No, that's not what would happen. A ring-shaped black hole is impossible. What would happen is described above.
 
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  • #7
If the black hole is already extremal or nearly so, and the ring is orbiting fast enough, the black hole won’t be able to absorb the ring since then the result would be a super-extremal black hole. The only way the ring could be absorbed would be if it lost some of its angular momentum.
 
  • #8
A Puzzlement said:
If the black hole is already extremal or nearly so, and the ring is orbiting fast enough, the black hole won’t be able to absorb the ring since then the result would be a super-extremal black hole.

No, because the ring has mass (energy) as well as angular momentum. I strongly suggest that you run some numbers instead of guessing.
 

1. What is a rotating black hole with a ring?

A rotating black hole with a ring, also known as a Kerr ring, is a theoretical type of black hole that has a spinning ring of matter around its event horizon. This is different from a traditional black hole, which has a singularity at its center and no surrounding matter.

2. How does a rotating black hole with a ring affect spacetime?

A rotating black hole with a ring causes distortions in the fabric of spacetime due to its strong gravitational pull. This can result in phenomena such as frame-dragging, where the rotation of the black hole causes space and time to be dragged along with it.

3. Can a rotating black hole with a ring exist in our universe?

While rotating black holes with rings are currently only theoretical, there is evidence that they may exist in our universe. Observations of active galactic nuclei, which are thought to contain supermassive black holes, suggest that they may have a rotating ring of matter around them.

4. How do rotating black holes with rings form?

The formation of rotating black holes with rings is still not fully understood. They may form from the collapse of a rapidly rotating star, or through mergers of two black holes with aligned spins. Further research and observations are needed to fully understand their formation.

5. What is the significance of studying rotating black holes with rings?

Studying rotating black holes with rings can provide valuable insights into the nature of gravity, spacetime, and the behavior of matter under extreme conditions. This research can also help us better understand the formation and evolution of black holes, which are important objects in our universe.

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