The cataclysmic collision of black holes is a frequent occurrence in space, according to a team of international scientists that has just detected gravitational waves for the second time in history.

Key facts about the detection: Like the first signal, this new signal comes from merging of two black holes

Like the first signal, this new signal comes from merging of two black holes These black holes were smaller, so the signal is weaker but longer lasting

These black holes were smaller, so the signal is weaker but longer lasting They merged 1.4 billion years ago — 100 million years before the first detected merger

The waves are tiny ripples in space and time formed by the merging or "coalescence" of two black holes. They have opened up an entirely new field of astronomy.

Scientists can use gravitational waves to look billions of years back in time into the vast majority of space that was previously invisible.

This surprising new find was captured in the United States on Boxing Day last year and came just four months after the same team detected these waves for the very first time. It took months of analysis to confirm the most recent discovery.

There may have even been a third detection, although scientists are less certain.

The discovery, announced in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration — a team of more than 1000 scientists from more than 90 universities around the world.

One of those scientists was Professor David Blair from the University of Western Australia, who said the find was "fantastically significant".

"The first signal was fantastic, it was almost better than we could have ever expected beyond our wildest dreams — but it could have been a lucky fluke and we might never have seen another signal in 100 years or 1,000 years," he said.

"So you have to see more to get some idea of how many signals are out there and to get an idea of what we can expect in the future as we improve the detectors.

"This signal tells us that there's going to be a flood of gravity wave signals coming in in the next few years as the detectors are improved."

The gravitational wave detectors — located in the US and Italy — will be upgraded later this year, opening up entirely new possibilities.

"Detecting a second burst of gravitational waves means we are well on the way to being able to map the populations of black holes in our universe," said Associate Professor Peter Veitch, Head of Physics at the University of Adelaide.

"Perhaps even more excitingly, who knows what else will be revealed as we continue to improve the sensitivity of the detectors?"

The first detected burst of gravitational waves came from a black hole merger which emitted more energy in one second than all the stars in the universe combined.

This second event, while not as powerful, produced a massive spinning black hole 21 times the mass of the sun, with the waves travelling 1.4 billion years to Earth.

Up until now, virtually everything we have been able to spot in the universe has been thanks to light — either with our own eyes or powerful antennae.

Astronomers can now study these ripples, and use gravity to "see" things that were previously invisible.

The first detection of gravitational waves was a milestone in physics and astronomy, confirming a major prediction of Albert Einstein's 1915 general theory of relativity.

Einstein's general theory of relativity tells us that gravity is the curvature of space and time.

The stronger the gravity an object has, the greater the deformation of space and time it causes.

Gravitational waves form when objects with strong gravity accelerate. As a big mass accelerates, ripples of space travel away from it at the speed of light.

They are not like light waves travelling through space, they are actual waves in space: rhythmic stretching and squeezing of the fabric of space-time.

All objects sitting in the path of gravitational waves rhythmically move further apart and closer together as the space they exist in is stretched and squeezed.

The strongest gravitational waves — the only ones we have a hope of detecting — are formed when objects with enormous gravity undergo dramatic acceleration.

In both cases so far, it has been two black holes merging to form an even bigger black hole.

The ripples from these strongest waves are so small — only a fraction the size of an atom — that Einstein himself thought they had to be beyond our technology.

Detecting them is a monumental achievement.