**Black holes are as extreme as anything can get.** When a massive structure can no longer sustain its own gravity, it will collapse to a point known as a singularity. For example, a massive star after it has gone supernova may leave one of these singularities behind, a remnant of massive star death, sucking any local matter into a one-way trip to the guts of space-time.

At a certain point, when light itself succumbs to the black hole’s gravity, an event horizon forms, beyond which universal physics breaks down; we have very little idea about what lies inside the event horizon. All we do know is that you don’t want to fall into one, you’d be stretched and spaghettified. Spaghettification is due to extreme (and when I say extreme, I mean *as-extreme-as-it-can-get*) tidal forces between your head to your toes.

So, the message is: *Don’t play with black holes, it can only end in tears*.

Now the *Black Hole Health & Safety* lecture is over, it’s time to talk about “black rings”. Under certain conditions, black holes may not be the mathematical singularities we once knew and (thought we) understood.

In a recent publication by Masashi Kimura at Osaka City University in Japan, the black ring idea is explored in 5-dimensional space. In the space-time we know and love, there are three spatial dimensions and one temporal dimension. We are *four-dimensional creatures*. When string theory came along in the 1980’s we really began to appreciate that there could be more than the four dimensions we live in.

Previously, cosmologists have entertained the thought that black rings may exist in our 4D space-time. However, the big problem comes when trying to understand how these structures maintain their shapes; surely they should simply collapse and form your regular black holes? Actually, it depends on how big they are and how the competing forces balance out.

As the Universe is expanding, it is thought black rings could exist if they are of scales similar to the cosmological constant (this constant was derived by Einstein to explain a “flat” Universe, but later it was found the constant was required to characterize the universal expansion as observed by Edwin Hubble in 1929). If a black ring exists in 4D space-time, its gravitational collapse would be countered by the expansion of space-time (as characterized by the cosmological constant).

The only analogy I can relate this to in the terrestrial world is bubble rings (or, indeed, smoke rings). When under water, a bubble will rise to the surface. However, under the constriction of surface tension, the bubble will form the smallest possible shape. When a bubble ring is produced, there needs to be a balance between surface tension and a vortex. The surface tension pulls in, while the vortex maintains the bubble ring shape, pushing out.

In the case of the black ring, gravity is pulling inward, while the expansion of space-time is countering it, pushing out. In this situation, in an expanding Universe, there could be enduring examples of black rings out there.

In Kimura’s research, not only are black rings a possibility, there could be a number of different complex shapes that could form when considering these extra dimensions. When the Universe was young, multiple interacting black rings may have been possible, eventually coalescing to form black holes.

Although this research is very interesting, it is hard to imagine how we could observe these higher-dimensional black rings. Would we see them as a singularity (i.e. a black hole) in our 4D space-time? Or would they even be unobservable for lower-dimensional beings such as ourselves?

Publication: *Dynamical Black Rings with a Positive Cosmological Constant*, Masashi Kimura, 2009. arXiv:0904.4311v2 [gr-qc]

**Via: arXiv blog**