Scientists have shown how a ring-shaped black hole could cause Einstein's general theory of relativity, a foundation of modern physics, to break down - assuming the universe contains at least five dimensions.

The researchers, from the University of Cambridge and Queen Mary University of London, have successfully simulated a black hole shaped like a very thin ring, which gives rise to a series of 'bulges' connected by strings that become thinner over time.

These strings eventually become so thin that they pinch off into a series of miniature black holes, similar to how a thin stream of water from a tap breaks up into droplets. Ring-shaped black holes were 'discovered' by theoretical physicists in 2002, but this is the first time that their dynamics have been simulated using supercomputers.

Should this type of black hole form, it would lead to the appearance of a 'naked singularity', which would cause the equations behind general relativity to break down. General relativity theory tells us that matter warps its surrounding space-time, and what we call gravity is the effect of that warp.

In the 100 years since it was published, general relativity has passed every test that has been thrown at it, but one of its limitations is the existence of singularities. A singularity is a point where gravity is so intense that space, time, and the laws of physics, break down.

General relativity predicts that singularities exist at the centre of black holes, and that they are surrounded by an event horizon - the 'point of no return', where the gravitational pull becomes so strong that escape is impossible, meaning that they cannot be observed from the outside.

"As long as singularities stay hidden behind an event horizon, they do not cause trouble and general relativity holds - the 'cosmic censorship conjecture' says that this is always the case," said study co-author Markus Kunesch, a PhD student at Cambridge's Department of Applied Mathematics and Theoretical Physics (DAMTP).

In case a singularity existed outside of an event horizon, not only would it be visible from the outside, but it would represent an object that has collapsed to an infinite density, a state which causes the laws of physics to break down, researchers said.

Theoretical physicists have hypothesised that such a thing, called a naked singularity, might exist in higher dimensions. "If naked singularities exist, general relativity breaks down," said co-author Saran Tunyasuvunakool, also a PhD student from DAMTP.

"And if general relativity breaks down, it would throw everything upside down, because it would no longer have any predictive power it could no longer be considered as a standalone theory to explain the universe," said Tunyasuvunakool. The research was published in the journal Physical Review Letters.