# B Are black holes perfect spheres?

1. Feb 27, 2017

### Alanay

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

2. Feb 27, 2017

### Comeback City

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

3. Feb 27, 2017

### lifeonmercury

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

4. Feb 27, 2017

### Comeback City

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

5. Feb 27, 2017

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

6. Feb 27, 2017

### Comeback City

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)?

7. Feb 27, 2017

### phinds

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

8. Feb 27, 2017

### Staff: Mentor

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).

9. Feb 28, 2017

### Comeback City

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

10. Feb 28, 2017

### rootone

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

11. Feb 28, 2017

### Comeback City

AAAARGH! I'm sorry for my pitiful question

12. Mar 3, 2017

### Rubidium_71

13. Mar 3, 2017

### Chronos

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

14. Mar 3, 2017

### Frosted Flake

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

15. Mar 8, 2017

### Thomas Wown

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