An intriguing new hypothesis suggests some black holes could have formed before the formation of our universe.

The work by Professor Bernard Carr from Queen Mary University in London and Professor Alan Coley from Canada's Dalhousie University, examines a cosmology in which the universe goes through cycles of birth and death.

According to their work published on the pre-press website arXiv.org, some black holes could be remnants of a previous universe that collapsed in a big crunch and was then reborn in the big bang - 13.7 billion years ago.

Called primordial black holes, they would be formed in the hyper dense conditions existing in the moments after the big bang. That makes them even more exotic than other black holes formed from the collapse of massive stars or at the centre of galaxies.

Professor Carr and Professor Coley say if the universe expands and contracts in cycles of big bangs and big crunches, some primordial black holes may survive.

They reached their conclusion after thinking about what might happen in the moments before a big crunch.

Rather than everything merging back into a singularity, Professor Coley and Professor Carr speculate the densities reached as the universe transitions from big crunch to big bang, mean primordial black holes between a few hundred million kilograms and about the mass of our sun, could survive as separate entities.

So far primordial black holes only exist in theory, and even if scientists do eventually detect one, Professor Carr and Professor Coley admit there would be no way of determining if it was born in our universe or came from a previous epoch.

Pushing the boundaries

Dr Tamara Davis, an astrophysicist and theoretical cosmologist with the University of Queensland, says the work is interesting, but extremely speculative.

She says it pushes the boundaries of existing theories far beyond what those theories are capable of describing.

"We know our theories break down when you get to the densities and pressures existing near the big bang," she said.

"We don't know the physics of what would happen in this bounce, or even if the bounce occurs at all. It's just one of the possible theories of how our universe began, and it's a very speculative one."

But according to Dr Davis, theories that predict these bounces also allow for differences in the fundamental constants of nature.

"The strength of gravity, the speed of light, or the strength of the electric charge could be different in different universes," she said.

"So it becomes even more speculative to say black holes from one universe could exist in another.

"But this kind of research is also very important because it's only by pushing the boundaries of our current theories that we can find out where the weaknesses are and make progress in figuring out how to solve those weaknesses."