B Are black holes perfect spheres?

[Alanay]

Since it is practically impossible to artificially create a perfect sphere, are black holes the closest thing?

 

[Comeback City]

Since it is practically impossible to artificially create a perfect sphere, are black holes the closest thing?

I believe they are, but better to let one of the experts here clarify it.

 

[lifeonmercury]

My understanding is that a black hole is a singularity but the borders of the event horizon surrounding it form a perfect sphere.

 

[Comeback City]

My understanding is that a black hole is a singularity but the borders of the event horizon surrounding it form a perfect sphere.

Yeah I believe the OP is talking about the event horizon.

 

[Vanadium 50]

If the black hole is rotating, the EH is axially, not spherically symmetric.

 

[Comeback City]

If the black hole is rotating, the EH is axially, not spherically symmetric.

So just to build off of this, would a faster rotation speed of the BH lead to a more elongated black hole (along its axis)?

 

[phinds]

So just to build off of this, would a faster rotation speed of the BH lead to a more elongated black hole (along its axis)?

I think it's more disk-like, not more elongated along the axis.

 

[Nugatory]

Usually when people say "a black hole", they mean the Schwarzschild solution to the Einstein field equations, which describes a static and spherically symmetrical spacetime. A Schwarzschild black hole is not rotating (this is implied by spherical symmetry) and its event horizon is indeed a perfect sphere.

Of course this has to be an approximation; any real black hole will surely have some amount of rotation. A rotating black hole is described by the Kerr-Newman solution (google will find more information); Kerr-Newman black holes are not perfectly spherical and also do strange things like frame-dragging. These effects are most pronounced near the horizon, so the Schwarzschild solution is a good approximation for many situations. For example, the precession of Mercury, deflection of light by the sun, and the Shapiro effect are all adequately explained by the Schwarzschild solution applied to the sun and ignoring its rotation. (The sun is not a black hole of course, but the Kerr-Newman and Schwarzschild solutions apply to things that aren't black holes too).

 

[Comeback City]

I think it's more disk-like, not more elongated along the axis.

But is it the ergosphere that is disk-like, or the event horizon itself?

 

[rootone]

But is it the ergosphere that is disk-like, or the event horizon itself?

Aaargh ... frame dragging, that really gets on my nerves.
/jk

 

[Comeback City]

Aaargh ... frame dragging, that really gets on my nerves.
/jk

AAAARGH! I'm sorry for my pitiful question

 

[Rubidium_71]

According to this:
https://en.wikipedia.org/wiki/Ring_singularity
it could even possibly be a ring shape.

 

[Chronos]

IIRC the Kerr-Newman metric is mathematically valid, so I concur with Nugatory.

 

[Frosted Flake]

I'll go check. I'll let you know what I find out.

 

[Thomas Wown]

It can't be a perfect sphere. Too much gravity around the Universe so the shape will definitely change accordingly.