system
Given the following post, respond as if you're commenting on Reddit:
human
What is the shape of a black hole?

Hello,

i have been very interested in the universe lately. i love to watch tv shows like "the universe" and stuff. one thing that i cant quite get my head around is the shape of a black hole. in this tv shows the black holes are always shown as a flat disc. but i cant quit understand how it can be flat when there is so matter inside.
can you pls explain to me what the form of a black hole is?
gpt
The shape of the singularity at the center of the black hole is unknown.  For our purposes, we can treat it as a point source with mass equal to the mass of the black hole.

The black hole itself is spherical, as the black hole is defined by its **event horizon**, the radius at which nothing, not even light, can escape.  

A spinning black hole, which is the case found in nature, as everything has non-zero angular momentum, is described by the **Kerr metric**, a solution of Einstein's field equations.  This metric predicts a region outside the event horizon called the **ergosphere**.  Contrary to popular belief, the ergosphere is *not* an "extended event horizon".  The event horizon, by definition, is the point at which no information can be extracted from the black hole within.  The ergosphere is called the ergosphere because you can extract work from it.  An object falling into the ergosphere can, in principle, escape.  The ergosphere is the region around a black hole in which **frame-dragging** becomes significant.

The disk you are thinking of is the **accretion disk** of a "feeding" black hole.  Most feeding black holes we know of are supermassive black holes at the nuclei of galaxies, and so are known as **active galactic nuclei** (AGNs).  These are black holes that are millions or even billions of times as massive as the Sun.  This accretion disk is not within the black hole,  however.  The immense amount of gravitational potential energy of infalling matter is released in the form of friction in the accretion disk, and the energies involved are so great that the accretion disk heats up enough to emit ultraviolet light.  This, combined with other interesting products of accretion physics, such as an X-ray emitting corona and a radio-emitting jet, is why AGNs are relatively easy to spot, even billions of light years away.