And then there were three.

Astronomers have detected a third gravitational wave, a tiny ripple in space-time that swept past Earth at the speed of light in just 0.4 seconds on January 4.

Its source? The collision and coalescence of two black holes 3 billion light years away, forming a larger black hole with the mass of nearly 50 suns.

The first gravitational waves were announced last year, providing evidence for the last unproven prediction emerging from Albert Einstein's general theory of relativity.

This latest discovery tells us more about the nature of black holes – and maybe dark matter – and shows gravitational-wave astronomy has arrived as a new window on the universe.

The findings were announced on Friday by astronomers from LIGO, the Laser Interferometer Gravitational-wave Observatory in the United States and published in Physical Review Letters.

The 1000-strong LIGO team includes 38 Australian researchers at the Australian National University, University of Western Australia, Monash University, University of Melbourne and University of Adelaide.

LIGO scientists said the discovery provided evidence that black holes exhibit a spin property.

"This is the first time that we have evidence that the black holes may not be aligned, giving us just a tiny hint that pairs of black holes may form in dense stellar clusters," says Bangalore Sathyaprakash of Penn State University, one of two lead editors for the publication.

Professor Susan Scott from ANU said: "It's possible this is a binary system of black holes formed in the early universe, which contributes significantly to the dark matter of the cosmos."

Gravitational waves were predicted by Einstein in 1916 as part of his general theory of relativity. In his groundbreaking work, Einstein showed that space-time would be distorted by massive objects accelerating around each other – such as binary neutron stars, or coalescing black holes.

However, the mathematics show that even huge events at scales almost beyond our imagination would produce very small distortions in space.

Einstein himself thought we'd never detect them.

However, the perpendicular four-kilometre laser arms at LIGO have been able to detect the effects of the waves at scales less than the width of a single proton.

Professor Scott said we need to study the effects of strong-field gravity around such events to test our understanding of general relativity.

"With each event we detect we are able to push things a bit more," Professor Scott said. "We know general relativity is not a theory of everything. It will have to fit in with quantum mechanics."

She said it will be through studying extreme events using gravitational-wave astronomy that we may find areas where Einstein's theory cannot explain results.

It is hoped that by uniting our understanding of the physics of the very large, explained by relativity, and the very small, explained by quantum mechanics, a new, unified understanding will emerge.

Professor Scott said when LIGO first started hunting for gravitational waves, it was thought the first events to be detected would be rotating neutron stars, the highly dense remnants of large stars.

"It didn't turn out that way – and that's what so great about science," she said.

"What will be really exciting will be if we discover a gravitational-wave event that doesn't match any of our models – we will have found something new."

In the study published on Friday, the two black holes detected were 31.2 and 19.4 solar masses. After spinning around each other and colliding, they formed one massive black hole just 289 kilometres wide with the mass of 48.7 suns.

Those sums mean that two solar masses – 4000 trillion trillion tonnes – were ejected from the cataclysmic event in the form of radiating gravitational waves.

"The event released more energy in its last few orbits than that of rest of the entire universe, yet when the ripples passed the LIGO detector they made it vibrate by just one attometer, or 0.000000000000000001 metres," said Professor Matthew Bailes, director of the new Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav).

Australia is emerging as an important centre for the study of gravitational waves. The establishment of OzGrav means Australian researchers are in at the ground floor in this new field of astronomy.

In April, the executive director of LIGO, David Reitze, was in Australia lobbying for one of the next generation gravitational wave observatories to be built here in the southern hemisphere.

OzGrav's deputy director, Professor David McClelland from ANU, said: "Our quest to extend LIGO to detect other types of violent events, such as those from neutron stars, drives us to develop new technologies such as quantum squeezing optical devices to reach further into the universe."

Professor Scott said Australia is playing a role in designing instruments for the third generation detectors as well as finding better ways to search through the data for gravitational wave events.

"There is growing support for a detector in Australia," she said. "Chief scientist Alan Finkel is a supporter and the case is gathering momentum because it makes sense: we are in the southern hemisphere, we have plenty of space and we have the expertise."