Is there really a black hole in Eve Online?

I've heard some people mention a black hole existing in Eve (not a wormhole). Does it really exist or is it some unfounded rumor? Where is it?

If you mean a functional black hole, sort of - but in terms of lore (and tourist attractions), the Eve Gate is:

a giant natural wormhole located in the New Eden System in the Genesis Region. Surrounded by a strong magnetic field, ship travel is impossible close the celestial object, and the now unstable wormhole is impassable. Famed for being the source of all life in the EVE cluster and used to lead to the Milky Way galaxy. Its collapse caused the worst disaster in EVE’s history, when the small human colonies of EVE were cut from support from the mother galaxy, destroying most life in the cluster.

Plus a video of Eve Gate, which you can visit. My corporation (and many others) periodically take a trip out there - people leave cans/markers, etc. to commemorate their visit.

Some people do claim there are systems with black holes, so maybe.

Certain systems in Wormhole space have a black hole in them, which significantly affects certain ship systems. Other than that, it's just a visual however - you can't warp towards it or get caught in the event horizon.

In Winter 2011 expansion they are also making the solar system backgrounds actually modeled. This means the black holes, nebulae etc visible on the sky are actually ingame 3D objects you see from some angle.

I don't think they will have many game-mechanical effects, though, so if you are after that, no luck.