What are the odds on Black Saturns? Only your bookie can say...

* 20:18 13 February 2007
* NewScientist.com news service
* Stephen Battersby
If we ever make black holes on Earth, they might be much stranger objects than the star-swallowing monsters known to exist in space. According to a new theory, any black hole that pops out of the Large Hadron Collider under construction in Switzerland might be surrounded by a black ring – forming a microscopic "black Saturn".

A black hole and a black ring can co-exist, in theory, as long as they are set spinning, say Henriette Elvang of MIT in Cambridge, US, and Pau Figueras of the University of Barcelona in Spain. "If you just had a ring, it would collapse. It's essential that it rotates to keep balanced," Elvang told New Scientist.

Just like the central black hole, the ring would be defined by its event horizon, a boundary beyond which nothing can escape the object's gravity. The ring could be thin like a rubber band or fat like a doughnut, and the rotation would flatten it – "like a doughnut that you have squashed," says Elvang. The spinning ring would also drag space-time around with it, making the central black hole spin as well.

The black Saturn can only exist in a space with four dimensions, rather than the three we inhabit. In 3D, a black ring is impossible, so there are no big black saturns out there for astronomers to spot – but at a microscopic level, they might really exist.
Ring sizes

Some attempts to unify the forces of nature, notably string theory, involve extra dimensions of space. The extra dimensions are usually thought to be curled up tight, so small as to be inaccessible, but in some theories they can be big enough – maybe a fraction of a millimetre in size, maybe infinite – to probe with high-energy experiments. They remain hidden from our eyes because although gravity can reach out into these dimensions, all other forces are confined to our 3D world.
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