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Are Black Holes Necessarily Spherical?

Dorfl

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If two black holes were orbiting each other at a very close distance, would they still be spherical, or would the event horizons become more drop-shaped, just like ordinary binary stars do?
 
The one in my washing machine seems to be dustbin - shaped.
Or at least sock shaped.
 
No they are not spherical if they have spin
Amy Barger:
"[FONT=Verdana, Arial, Helvetica]If we could 'see' black holes, they would be of two different types," Barger says. "One type would have the symmetry of a sphere. The other type would have the symmetry of a top. The latter type of black hole possesses the axial-symmetric shape because it has spin."

from http://www.space.com/scienceastronomy/mystery_monday_030901.html
[/FONT]
 
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Wudang said:
No they are not spherical if they have spin
Amy Barger:
"[FONT=Verdana, Arial, Helvetica]If we could 'see' black holes, they would be of two different types," Barger says. "One type would have the symmetry of a sphere. The other type would have the symmetry of a top. The latter type of black hole possesses the axial-symmetric shape because it has spin."

from http://www.space.com/scienceastronomy/mystery_monday_030901.html
[/FONT]
Click to expand...

It seems like Wikipedia agrees with that:
Wikipedia said:
Rotating black holes have distorted, nonspherical event horizons.
Click to expand...

I can't find anything about binary black holes, though.
 
The reason is due to a uniform gravitational pull, which nothing can escape apart from virtual particles and hypothetical tachyons. The uniform pull does not differ on area part of the surface area of the black hole.
 
Singularitarian said:
Yes, the are necesserily sphrical. Always.
Click to expand...

Once nice thing about Sing is you can always rely on him to be wrong.... no, they certainly are not always spherical. Rotating black holes (and all real black holes will be rotating at least a little) are not spherical. Black holes that have just absorbed something are not spherical. Black holes merging are not spherical. Etc.

In general they behave not unlike droplets.
 
Singularitarian said:
The reason is due to a uniform gravitational pull, which nothing can escape apart from virtual particles and hypothetical tachyons. The uniform pull does not differ on area part of the surface area of the black hole.
Click to expand...
But in the case of a binary pair the pull would not be uniform, would it?
 
I had usually spin not to be so effective on the black holes structure, again due to the gravitational strength.
 
Singularitarian said:
I had usually spin not to be so effective on the black holes structure, again due to the gravitational strength.
Click to expand...
Do I interpret this correctly as you having thought spin not to have any noticeable effect on the black hole's structure, due to the vastly greater strength of the gravitational force?

That might be true-ish: I don't know if any black hole will rotate enough to differ very much from the spherical in practice. But in the case of a binary pair, won't there be at least a short while, as they spiral in towards each other, when they are very noticeably non-spherical?
 
Singularitarian said:
If anything, they would be pulled together uniformly. Objects moving close to black holes are in a state of free fall.
Click to expand...
I'm not sure what you mean by them being "pulled together uniformly". But the important thing isn't how the black holes are being pulled, is it? The question is how other things are affected by the gravitational force from the holes, and I do not think it will decrease uniformly with radial distance in the binary example.
 
Dorfl said:
That might be true-ish: I don't know if any black hole will rotate enough to differ very much from the spherical in practice.
Click to expand...

It's not. There is a limit to how much a black hole with a given mass can spin, called the extremal limit. Near that limit the shape and spacetime structure of the hole is very different from that of a non-rotating one, and it is believed that nearly all astrophysical black holes come close to saturating the limit.

But in the case of a binary pair, won't there be at least a short while, as they spiral in towards each other, when they are very noticeably non-spherical?
Click to expand...

Yep - and after they've merged.
 
You know, black holes can even spin at the speed of light! Black hole spins vary from different star collapses.

Going back to the question, it is possible if they get close enough, they will begin to stretch, as you would expect any body coming close to the event horizon.
 
sol invictus said:
Once nice thing about Sing is you can always rely on him to be wrong.... no, they certainly are not always spherical. Rotating black holes (and all real black holes will be rotating at least a little) are not spherical. Black holes that have just absorbed something are not spherical. Black holes merging are not spherical. Etc.

In general they behave not unlike droplets.
Click to expand...

I had no idea that their shape would be much different after absorbing something, but now that you say it, I realise that it would have to change slightly. Do they sort of oscillate after absorbing something, or what happens?
 
Only when they get close together, are the tidal forces taken into account, otherwise, your structure can be uneffected, but the gravitational pull is pulling all the particles in your body at the same rate.
 
sol invictus said:
It's not. There is a limit to how much a black hole with a given mass can spin, called the extremal limit. Near that limit the shape and spacetime structure of the hole is very different from that of a non-rotating one, and it is believed that nearly all astrophysical black holes come close to saturating the limit.
Click to expand...
What happens if you try to make it spin faster?

Yep - and after they've merged.
Click to expand...
Cool, what happens then?
 
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