The collision occurred nearly 2 billion years ago, but it was so far away that its shockwave has only just reached us.

This is the fourth confirmed detection made by an international team investigating Einstein's Theory of General Relativity.

Sheila Rowan of Glasgow University, UK, said the team was now on the threshold of a new understanding of black holes.

"It is tantalising to see this new story of how black holes formed and evolved through history of the cosmos," she told BBC News.

"This information is almost within our grasp but we are not quite there yet."

Gravitational waves are ripples in space and time caused by cataclysmic events in the Universe such as the collision of two black holes or the explosion of a giant star.

They can be thought of as ripples in a pond caused by a pebble. But the pebble is the cataclysmic event and the fabric of the Universe, including everything and everyone on Earth is the water. Just as the water ripples, all matter is momentarily distorted as the gravitational wave passes through. But the distortions are minute - the entire Earth is stretched and squeezed by less than the width of an atom.