# Thread: A sphere of black holes.

1. Join Date
Oct 2005
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## A sphere of black holes.

Let me describe a rather odd (hypothetical) experiment:

You take a very huge amount of black holes. You throw them from all directions towards a certain point. At a certain distance of that point, the event horizons of the black holes make contact with each other.

Will this (temporarily) create a hollow black hole sphere? Would there be any way to stop this sphere from collapsing (from the inside or the outside)?

2. No.

I just tried it.

Now the apple I was saving for break time has gone. Curse excessive gravity.

3. Order of Kilopi
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Eech. It wouldn't be plesent in there. They would all collapse into each other and you would be left with one big BH. If you had two black Holes orbiting each other there would be a 'calm spot' between them where a probe could 'stand'. To much one way or the other, and it gets drawn in.

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Very interesting question. It is similar to something I have wondered about for years. If the very center of the earth was hollow, say for a mile diameter, what would happen to someone placed at the exact center of the hollow earth? This same scenario would exist within the black hole sphere I assume. Would it result in negative G's. In the case of the black holes would it be extremely negative G's?

5. Originally Posted by publiusr
Eech. It wouldn't be plesent in there. They would all collapse into each other and you would be left with one big BH. If you had two black Holes orbiting each other there would be a 'calm spot' between them where a probe could 'stand'. To much one way or the other, and it gets drawn in.
I wonder if there really would be a 'calm spot' or point of equal and opposite gravitational attraction except as a transitory state - ie, the point of balance would be constantly shifting in response to changes in the black holes ...

In thinking about a black hole, meaning the sphere defined by the event horizon rather than the postulated singularity at its core, is it correct to assume that the "surface" (horizon) is stable and quiescent? Would it really look like some freaky 'black marble' in space? Or would the "surface" be choppy and active ... with relativistic 'eruptions' or 'prominences' ... especially if material is infalling...?

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The surface does not exist. Gravitational lensing allows stars behind the BH to be seen, so no black marble. All radiation that we pick up from material falling into a black hole is quite far from the event horizon. So that's all normal spacetime physics that we're dealing with.

Eruptions from the Bh itself?

7. Hi alainprice,
Originally Posted by alainprice
The surface does not exist.
Please do not confuse ["surface" (horizon)] with with a solid or otherwise material surface - or give it a name you are comfortable with ... or, are you stating that the event horizon does not exist?

Originally Posted by alainprice
Gravitational lensing allows stars behind the BH to be seen, so no black marble.
I'm not sure it works that way up close ... but perhaps you can explain how that would appear different to a freaky black marble?

Originally Posted by alainprice
All radiation that we pick up from material falling into a black hole is quite far from the event horizon. So that's all normal spacetime physics that we're dealing with.
and this is relevant in what way?

Originally Posted by alainprice
Eruptions from the Bh itself?
localised responses in the event horizon to transitory increases in mass...?

8. To perhaps expand (or clarify?) the thought experiment: Say we place BHs evenly in a sphere, and through some imaginary mechanism also make it so it won't collapse. That is, a "hollow black hole sphere". Now, I think the math works out so that inside a sphere, gravity will cancel out at each point. If this is true, not only an approximation for low gravity wells, could a person live inside this sphere?

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Black holes can be electrically charged, can't they?
If they were positively charged, and the sphere would be sufficiently big, and the holes were going sufficiently slow, wouldn't a large positive charge inside be able to stop them from collapsing?

10. Order of Kilopi
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Originally Posted by WSteveBro
Very interesting question. It is similar to something I have wondered about for years. If the very center of the earth was hollow, say for a mile diameter, what would happen to someone placed at the exact center of the hollow earth? This same scenario would exist within the black hole sphere I assume. Would it result in negative G's. In the case of the black holes would it be extremely negative G's?
That basic scenario (minus the black hole detail) has been discussed a few times in the forum. Do a search for "hollow Earth", and you should find the answers.

11. An Explosion a really big one. No real repelling going on until after the collision at least. All black holes collision velocity will increase exponentially with decreasing distance. Forget having some sort of safe or came zone in the area. As at this center point would have the combine gravitational pull of all the stars. The center point of two equal mass/size ratating body is equidistant from the bodies. Put something in that position and it would experience some seriouse gravitational flexing. So that been said having the proper amount of quantum singularities on a collision course in a manner as you described will be violent for anything at location T-0.

So in the spirit of Phonicboom I decided to try it also. This is what happened. First I could'nt find enough black holes, and the few I found I couldnt move them. So I settled for Neutron stars. So I spunn them up and sent them towards each other. Then I put my roommate in the middle. Told him to tap morris code about what it felt like and this is what he said. First he was ripped to shred in equal parts to the direction of the stars. The on subatomic string particle that was still left and could not be distroyed anyfurther remained experiencing absolute zero as no energy could either be gained or further released un till it was annialated by the combine mass of those neutron stars colliding into it.

Now I find new roommate

12. I bet your roommate has my apple.

13. Your apple popped out in the past and my son ate it during his school snack time.

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Sorry, two event horizons meeting each other, think about it, if you can.
Nokton

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Black holes can be electrically charged, can't they?
Is it the black hole that is charged or the accretion disk that surrounds it? How could we perform the measurement? Even if it is charged, would that part of the universe outside the black hole's event horizon be affected?
Last edited by GOURDHEAD; 2005-Oct-18 at 05:37 PM.

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This doesn't work, I'm afraid.
Remember that the Schwarzchild radius of a black hole is proportional to its mass.
Take eight equal-mass black holes and place them at the corners of a cube, separated by 2x their individual Schwarzchild radius. They form a mass concentration that generates its own event horizon, radius 8x the radius of an individual black hole, and therefore 4x the side-length of the cube. That's well outside the perimeter of our cube of black holes.
So by the time our black holes are within "touching" distance, they've already merged into a larger black hole. Any theoretical observer at the centre of this system finds herself inside the event horizon, and therefore inexorably drawn to the forming singularity. She might get to see what eight singularities look like as they merge, but she'll never be able to tell anyone outside the event horizon.

Same argument applies as you increase the number of black holes - as you add vertices to a regular polyhedron, the vertex count always increases faster than the radius of the circumscribed sphere. So a sphere of black holes will always throw off a new event horizon before they get within a Schwarzchild radius of each other.

Grant Hutchison

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