# How deep and shaped is the depth of a black hole?

A common representation of a black hole is a black circle which if I'm correct, indicates its breadth.

This representation depicts it as a 'plate', so a really small depth compared to its breadth.

On this other representation, its depth has a funnel shape.

Question:

How deep and what shape has the depth of a black hole ?

• Relevant to funnel shape representations (there are actually at least two different kinds): Spacetime curvature illustration accuracy. – Stan Liou Nov 5 '14 at 20:32
• Nice question +1 – Juka Nov 6 '14 at 2:14
• Aybe - This question on Physics might interest you. – HDE 226868 Nov 14 '14 at 23:43

The first representation isn't depicting the black hole; it's depicting its accretion disk, which is indeed plate-shaped. The accretion disk is around the black hole, and - if it's a rotating (Kerr) black hole - it's perpendicular to the black hole's axis of rotation. Accretion disks are disk-shaped, and so the representation is disk-shaped.

The other is a common representation of a black hole, but it's misleading. It's an extension of the "rubber sheet" analogy, which describes the bending of spacetime. A heavy object, placed on a semi-taut sheet, will curve it a little bit. This represents ordinary matter curving spacetime. A black hole is represented in that image as bending spacetime by an infinite amount. The issue is that this representation embeds the two-dimensional representation of spacetime in three dimensional space, making it appear as if the black hole has this extra depth. Black holes are not embedded in an extra spatial dimension.

Note also that the small object moving near the edge of the black hole is also represented by a tiny funnel. The creator seems to have tried to take the analogy to the extreme, portraying the object's funnel as finite, and the black hole's as either extremely large or infinite, in an attempt to explain that light cannot escape from a black hole. It's not too accurate, but it works to get the point across.

By the way, black holes do have size (the central point singularities of non-rotating black holes are infinitely tiny, while the ring singularities of rotating black holes are in the shapes of infinitely thin rings). You might want to read up on event horizons. The radius of the event horizon of a non-rotating black hole is a finite number, the Schwarzschild radius. It is calculated as $$r_s=\frac{2GM}{c^2}$$

In this case, the event horizon is spherical. In rotating black holes, it may be in the shape of an oblate spheroid.

• Nice answer, even helped me. – Juka Nov 6 '14 at 2:09

Look at this picture.

!black-hole shape][1]

www.astro.umd.edu

As the star gets bigger, the bigger the black hole will go, it's event horizon goes lower, and its inside grows thinner.

Also, if the star is small, you will fell the gravitational pull from much further away. But with a much larger one like a super-massive black-hole, you will get closer without noticing anything much.

• @Juke Do you need help inserting the picture? That could get rid of the downvoter. – HDE 226868 Nov 6 '14 at 12:26
• By the way, my name us Juka, not Juke, and yes, I do need help – Juka Nov 7 '14 at 2:08
• Oh, shoot, sorry about getting the name wrong. Okay, what is the URL for the picture? – HDE 226868 Nov 7 '14 at 12:43