Black holes as a tube rather than a point?

[Neil9327]

I am a physics graduate, so I know a little. But I have forgotton most of it in the past 20 years.

I had the following thought experiment that I thought I'd share with you.

 

If you have a glass tube of hydrogen at 1 atmospheres pressure 1 meter in diameter 1000 light years long but with open ends then in the middle for quite a long time the hydrogen would remain stationary, because the escape pressure of the hydrogen would not reach the middle of the tube for many years.

 

Now increase the pressure of the hydrogen so that its density is high enough to have a noticible gravitational effect. Would this gravitational pull pull the hydrogen from one side to the other? No because at each point the influence of each side would be almost the same (the difference over 100 light years would be negligible).

 

Now increase the mass of hydrogen so that the centre of the cylinder has a gravitational potential energy to be so low that it becomes a black hole. Then surely you have a linear black hole that extends for 1000 light years.

 

Now take that black hole "string" and loop it round so that it forms a perfect circle, diameter 130 light years. Would this structure persist? Well there would be some faint gravitational force causing it to collapse into itself. But would this string have any longitudinal compression strength that might offset this shrinking.

 

And what if the whole thing was rotating? Would the centrifugal force cause the black hole "string" to stay in place?

 

So is it possible that there might be lots of black hole "strings" or "tubes" floating about space waiting to STRIKE!

[Riogho]

It sounds plausible. But I doubt there are tubes of hydrogen out there that are dense enough to become black holes.

 

However, I think the singularity in a rotating black hole is actually a ring. So that is kinda like a tube ;P

[ajb]

I thought it has been shown that you can only have black holes in 4-dimensional general relativity (related to Birkhoff's theorem?). In 5-dimensional (and above) black rings and similar can exist. I believe this is due to the extra symmetries you can have in higher dimensions.

 

If you are interested see Black Holes in Higher Dimensions by Roberto Emparan and Harvey S. Reall.