Distant black hole collision felt on Earth

A black hole collision 9 billion light years away was so powerful, the effects could be felt here on Earth.

Australian scientists analysing data from the US-based Advanced Laser Interferometer Gravitational-wave Observatory found the tell-tale ripples in spacetime caused by the merger of two black holes on July 29, 2017.

They have now formed a new black hole that's estimated to be about 80 times larger than the Sun.

"This event also had black holes spinning the fastest of all mergers observed so far," said Australian National University's Susan Scott.

"It is also by far the most distant merger observed."

Predicted by Albert Einstein a century ago, it's only been two years since scientists detected gravitational waves for the first time after years of trying. They're best described as tiny ripples or shockwaves in spacetime.

Prof Scott's team says they found another three black-hole collisions in August 2017, all happening between 3 and 6 billion light years away.

"These were from four different binary black hole systems smashing together and radiating strong gravitational waves out into space.

"These detections of black-hole collisions greatly improve our understanding of how many binary black hole systems there are in the universe, as well as the range of their masses and how fast the black holes spin during a merger."

Though a black hole 80 times the size of the sun sounds huge, black holes can get much bigger - the largest, known as supermassive black holes, are found at the centres of galaxies and can be billions of times bigger.

In contrast, a black hole with the same mass as our entire planet would only be about a centimetre across.

Because the gravitational waves travel at the speed of light, the fact the collisions happened so far away means they also happened a very long time ago.

Eventually scientists hope to be able to detect ripples in spacetime from as far back as the Big Bang which birthed the universe as we know it.