Black holes could be hiding in “perfectly balanced pairs”, mimicking a single black hole, according to a new theory by scientists.

Researchers from the University of Southampton, working with colleagues in Cambridge and Barcelona, have shown it is theoretically possible that the pairs of black holes are being held in equilibrium by a cosmological force.

Conventional theories based on Einstein’s theory of general relativity explain how black holes can exist on their own whereas pairs of the massive astronomical objects would eventually be thwarted by gravity attracting and colliding them together.

But the new study, published in the journal Physical Review Letters, suggests this theory only works if the universe is standing still but, in one which is constantly moving, the scientists believe pairs of black holes could be existing while masquerading as one.

A University of Southampton spokesman said: “Black holes are massive astronomical objects that have such a strong gravitational pull that nothing, not even light, can escape.

“They are incredibly dense. A black hole could pack the mass of the Earth into a space the size of a pea.

“Through complex numerical methods, the team behind this latest study show that two static (non-spinning) black holes can exist in equilibrium – their gravitational attraction offset by the expansion associated with a cosmological constant.

“Even in the acceleration of an ever-expanding universe, the black holes remain locked at a fixed distance from one another. As hard as expansion may try to pull them apart, the gravitational attraction compensates.”

Professor Oscar Dias, of the University of Southampton, said: “Viewed from a distance, a pair of black holes whose attraction is offset by cosmic expansion would look like a single black hole.

“It might be hard to detect whether it is a single black hole or a pair of them.”

Professor Jorge Santos, of the University of Cambridge, said: “Our theory is proven for a pair of static black holes, but we believe it could be applied to spinning ones too.

“Also, it seems plausible that our solution could hold true for three or even four black holes, opening up a whole range of possibilities.”

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