<p>The event horizon would be spherical. What is usually depicted in drawings is the accretion disk, where all the debris gather before entering the event horizon.</p>

CC BY-SA 3.0
2014-05-01T04:13:30.187Z
2014-05-01T04:13:30.187Z
LDC3
<p>It depends on whether the black hole is rotating or not. If it is, The <a href="https://en.wikipedia.org/wiki/Ergosphere" rel="nofollow noreferrer">ergosphere</a> and singularity are oblate spheroids. If not, both would be spherical. The event horizon is always spherical.</p>

<p>Accreting matter around a black hole would form an accretion disk, however this should not be mistaken for the black hole itself.</p>

<p><img src="https://i.sstatic.net/ZcQAL.gif" alt="enter image description here"></p>

CC BY-SA 3.0
2016-03-03T19:34:09.847Z
Specifically, all the things that black holes do (form, absorb things, merge, evaporate by Hawking radiation, gravitationally interact with other bodies, etc) conserve angular momentum. So in practice, a black hole rotates if the total of all the stuff that's fallen into it was rotating, because that's most of the angular momentum that the black hole has ever "seen" in its "life".
Steve Jessop
CC BY-SA 3.0
2014-05-01T18:26:08.887Z
Do we know what determines whether or not one rotates? Would it be mass or size?
rougon
CC BY-SA 3.0
2014-05-01T18:41:35.163Z
Formation: rotating black holes are usually formed from the collapse of a massive spinning star
christopherlovell
CC BY-SA 3.0
2014-05-02T01:27:58.513Z
Also merging black holes could sum their angular momentum.
Py-ser
CC BY-SA 3.0
2014-05-01T18:10:05.673Z
2014-05-01T18:10:05.673Z
christopherlovell
<p>It's complicated, and it depends on what you mean by "black hole".</p>

<p>In general, for a distant observer, the "black hole" is the event horizon - the surface within which there is no escape to the outside. The more massive the black hole, the bigger the event horizon.</p>

<p><a href="http://en.wikipedia.org/wiki/Event_horizon#Event_horizon_of_a_black_hole" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/Event_horizon#Event_horizon_of_a_black_hole</a></p>

<p><strong>If the black hole is not rotating</strong>, the event horizon is a sphere, plain and simple. In a perfect vacuum, and if the black hole is big enough (is not microscopic), looking at it you'll see a perfectly black, round "thing", with the stellar background behind it.</p>

<p><img src="https://i.sstatic.net/KT8eg.jpg" alt="enter image description here"></p>

<p>However, the background image near the black hole would be distorted as if seen through a bad lens. This would become apparent as you move around it. This is because the powerful gravity of the BH bends the rays of light. See the first half of this video:</p>

<p><a href="https://www.youtube.com/watch?v=8s-pWPqFQBE" rel="nofollow noreferrer">https://www.youtube.com/watch?v=8s-pWPqFQBE</a></p>

<p>If the black hole is not in a perfect vacuum, but is surrounded by various pieces of matter, it may capture that matter, and an accretion disk will grow around it.</p>

<p><img src="https://i.sstatic.net/JYTuV.jpg" alt="enter image description here"></p>

<hr>

<p><strong>If the black hole is rotating</strong>, things are a bit more complicated. This is an object described by the <a href="http://en.wikipedia.org/wiki/Kerr_metric" rel="nofollow noreferrer">Kerr metric</a>, and it has two important surfaces: the usual event horizon, and the outer skin of the <a href="http://en.wikipedia.org/wiki/Ergosphere" rel="nofollow noreferrer">ergosphere</a>:</p>

<p><img src="https://i.sstatic.net/5mVD3.png" alt="enter image description here"></p>

<p>Nothing can escape from within the event horizon. It is possible to escape from within the ergosphere if you rotate with the black hole - this is known as the <a href="http://en.wikipedia.org/wiki/Penrose_process" rel="nofollow noreferrer">Penrose process</a>.</p>

<p>I was not able to find visualisations of a Kerr (rotating) black hole, but it should look somewhat similar to a non-rotating one, except it would appear "flattened" at the poles, and bulging at the equator.</p>

CC BY-SA 3.0
2014-05-01T17:50:33.580Z
Thanks! That pretty much answers my question. I always saw images like this ( http://assets2.bigthink.com/system/idea_thumbnails/44789/headline/black%20hole%20SS.jpg?1339604441), where the object is shown as sinking down into a field, but it always made more sense if the "black" of a black hole looked more like your second image.
rougon
CC BY-SA 3.0
2014-05-01T17:56:41.310Z
That image is a map of the gravity field around a black hole, and it's quite misleading to a lot of people. There's no "funnel" there in reality. It's just a way of saying: the closer you get to the BH, the stronger the gravity; the depth of the "funnel" is meant as a measure of the field. But the "funnel" is not a thing.
Florin Andrei
CC BY-SA 3.0
2014-05-02T01:29:30.200Z
Well, actually we don't know it, right? Otherwise it wouldn't be a singularity, by definition.
Py-ser
CC BY-SA 3.0
2014-05-01T17:42:59.077Z
2014-05-01T17:58:17.097Z
2014-05-01T17:58:17.097Z
Florin Andrei
<p>I have always been curious about what black holes (or their event horizons) would look like if we could directly observe them. I notice that they tend to be depicted as flat holes in space but it seems to me that they would be spheres. Is there a scientific consensus on this. Or is it a vague question?</p>

<black-hole><space-time>
What shape are black holes theorized to be?
rougon
# What shape are black holes theorized to be?

(Asked by: username_0 on 2014-05-01)

I have always been curious about what black holes (or their event horizons) would look like if we could directly observe them. I notice that they tend to be depicted as flat holes in space but it seems to me that they would be spheres. Is there a scientific consensus on this. Or is it a vague question?

**Tags:** black-hole, space-time


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## 3 answers

### Answer by username_1 on 2014-05-01. Score: 4

The event horizon would be spherical. What is usually depicted in drawings is the accretion disk, where all the debris gather before entering the event horizon.


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### Answer by username_2 on 2014-05-01. Score: 4

It depends on whether the black hole is rotating or not. If it is, The [ergosphere](https://en.wikipedia.org/wiki/Ergosphere) and singularity are oblate spheroids. If not, both would be spherical. The event horizon is always spherical.

Accreting matter around a black hole would form an accretion disk, however this should not be mistaken for the black hole itself.

![enter image description here](https://i.sstatic.net/ZcQAL.gif)

> **Comments:**
> **username_0**: Do we know what determines whether or not one rotates? Would it be mass or size?  
> **username_2**: Formation: rotating black holes are usually formed from the collapse of a massive spinning star  
> **username_4**: Also merging black holes could sum their angular momentum.  
> **username_3**: Specifically, all the things that black holes do (form, absorb things, merge, evaporate by Hawking radiation, gravitationally interact with other bodies, etc) conserve angular momentum. So in practice, a black hole rotates if the total of all the stuff that's fallen into it was rotating, because that's most of the angular momentum that the black hole has ever "seen" in its "life".  

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### Answer by username_5 on 2014-05-01. Score: 4

It's complicated, and it depends on what you mean by "black hole".

In general, for a distant observer, the "black hole" is the event horizon - the surface within which there is no escape to the outside. The more massive the black hole, the bigger the event horizon.

<http://en.wikipedia.org/wiki/Event_horizon#Event_horizon_of_a_black_hole>

**If the black hole is not rotating**, the event horizon is a sphere, plain and simple. In a perfect vacuum, and if the black hole is big enough (is not microscopic), looking at it you'll see a perfectly black, round "thing", with the stellar background behind it.

![enter image description here](https://i.sstatic.net/KT8eg.jpg)

However, the background image near the black hole would be distorted as if seen through a bad lens. This would become apparent as you move around it. This is because the powerful gravity of the BH bends the rays of light. See the first half of this video:

<https://www.youtube.com/watch?v=8s-pWPqFQBE>

If the black hole is not in a perfect vacuum, but is surrounded by various pieces of matter, it may capture that matter, and an accretion disk will grow around it.

![enter image description here](https://i.sstatic.net/JYTuV.jpg)

---

**If the black hole is rotating**, things are a bit more complicated. This is an object described by the [Kerr metric](http://en.wikipedia.org/wiki/Kerr_metric), and it has two important surfaces: the usual event horizon, and the outer skin of the [ergosphere](http://en.wikipedia.org/wiki/Ergosphere):

![enter image description here](https://i.sstatic.net/5mVD3.png)

Nothing can escape from within the event horizon. It is possible to escape from within the ergosphere if you rotate with the black hole - this is known as the [Penrose process](http://en.wikipedia.org/wiki/Penrose_process).

I was not able to find visualisations of a Kerr (rotating) black hole, but it should look somewhat similar to a non-rotating one, except it would appear "flattened" at the poles, and bulging at the equator.

> **Comments:**
> **username_0**: Thanks! That pretty much answers my question. I always saw images like this ( http://assets2.bigthink.com/system/idea_thumbnails/44789/headline/black%20hole%20SS.jpg?1339604441), where the object is shown as sinking down into a field, but it always made more sense if the "black" of a black hole looked more like your second image.  
> **username_5**: That image is a map of the gravity field around a black hole, and it's quite misleading to a lot of people. There's no "funnel" there in reality. It's just a way of saying: the closer you get to the BH, the stronger the gravity; the depth of the "funnel" is meant as a measure of the field. But the "funnel" is not a thing.  
> **username_4**: Well, actually we don't know it, right? Otherwise it wouldn't be a singularity, by definition.  

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