Expert: Courtney Seligman - 7/30/2010

Question
Hi Courtney,

Depictions of black holes are usually funnel-shaped, "down-the-drain" illustrations of warped spacetime.

In reality, wouldn't a black hole be spherical, pulling in matter and spacetime at all points on the sphere?

Thanks,
Marc

Answer
Yes, it would be more spherical than not. There are a couple of complications that would affect the way it attracted matter, but the "funnel" is, as you note, a representation of the shape of space-time, rather than of the actual appearance of the object.

The two things that could affect the shape, insofar as you could "see" it, are (1) rotation of the "hole" and (2) rotation of the material around it. For (1), if the black hole was created from a rotating object, its event horizon might be an ellipsoid of revolution, rather than a sphere; and although the deviation from a spherical shape might be small, it could be significant in terms of some physical processes. For (2), unless the material falling into it was heading directly toward it, it would tend to rotate around it, forming an accretion disk, which would lie in the plane of rotation of the infalling material. For instance, if it were part of a binary star system, the material would tend to lie in the orbital plane of the star and the black hole. This can have very strong effects on any radiation emitted by the infalling material before it falls through the event horizon, into the "hole"; but those fall outside the scope of your question, and I have to leave in just a few minutes, and don't have time to discuss them right now. For a discussion of such things, you might read about accretion disk emitters, or send me another note late tonight or early tomorrow.