Black holes might be infinitely weirder than simply ultra-dense masses from which even light can't escape - they might actually be the end result of the collapse of five-dimensional objects known as black strings. Yeah...this one's going to get weird.
We only experience four dimensions - three spatial plus time - but certain cutting edge theories suggest there are many more dimensions that we simply can't perceive. Depending on which theory you buy into, there could be anything from 10 or 11 to 26 total dimensions, with all but the familiar four microscopic and thus hidden from our view. (There are also some theories that suggest there could be a second time dimension, but those are truly bizarre.)
There's no evidence for these hidden dimensions, but they do help hold together certain models of the universe. Physicists can also simulate what would happen if these dimensions did exist, and a team recently decided to tackle a strange cosmic structure known as a black string. A black string is a five-dimensional (including time) version of our more familiar four-dimensional black holes - picture a succession of spherical black holes placed one on top of the other to form a cylindrical shape, and that's basically what a black string is.
The simulation suggests black strings wouldn't last for very long, as even the slightest disturbance to part of the string would cause it to start collapsing. If the cylinder got squished at its center, this would begin splitting and separating the individual black holes, transforming the continuous string into a bunch of discrete black holes connected by tiny filaments of black string.
This process would go on repeating for some time, slicing the string into even still smaller and more numerous divisions, and the supercomputer running the simulation lacked the processing power to take it through to the end. But the researchers suspect the end result would actually be one gigantic black hole. It's unclear exactly how big these black holes could be, but perhaps the supermassive black holes at the center of galaxies are actually the final remains of black strings?
Of course, there's an even more basic question to consider: in our four-dimensional view of the universe, what exactly would be the difference between a black hole and black string? According to physicists, there really isn't, at least not in any way we can currently distinguish. All the black holes we see could actually be five-dimensional black strings...or even weirder objects, depending on just how many dimensions there are and how many play a role in the formation of black holes.
There's also the black Saturn, which would be a spherical black hole surrounded by a donut-shaped ring of stacked black hole. This arrangement would greatly resemble Saturn and its rings, hence its name. Or perhaps we should delete the middle black hole and just go with a black ring. There's no way to know until we can figure out how to detect and interact with these hidden dimensions - assuming they exist - but anyone who thinks the strangeness of black holes can be contained to just four dimensions might want to think again.