colliding black holes
Cataclysmic events such as the collision of black holes produce gravitational waves which can be detected on Earth. P. Marenfeld/NOAO/AURA/NSF

In 2015, astronomers detected gravitational waves for the first time in what was arguably one the biggest scientific discoveries of recent years, proving Einstein correct 100 years after he predicted them in his theory of general relativity.

Now, physicists have announced they have detected the waves – ripples in the fabric of space-time created by titanic events like black holes colliding – for only the fourth time ever. This is also the first time they have been observed by two separate detectors.

The observations in 2015 were made by the two LIGO detectors in the US, which contributed to the latest discovery along with Virgo, another detector based in Italy.

"Today, we are delighted to announce the first discovery made in partnership between the Virgo Gravitational-Wave Observatory and the LIGO Scientific Collaboration, the first time a gravitational-wave detection was observed by these observatories, located thousands of miles apart," said France Córdova, director of the US National Science Foundation. "This is an exciting milestone in the growing international scientific effort to unlock the extraordinary mysteries of our universe."

Detection by two different observatories on different continents is important as it allows astronomers to determine the location and distance of the event that caused the gravitational waves with around ten times more accuracy. The event in question was a cataclysmic collision of two rotating black holes – with masses 31 and 25 times greater than the Sun – that took place around 2 billion years ago.

Significantly, if these wave detection techniques are refined, scientists will be able to point their telescopes directly at the origin of the signals as soon as they are detected, allowing scientists to greater understand cataclysmic events, such as the collision of two neutron stars – an event many rumoured was the reason for today's announcement.

"This was a very strong first," said John Veitch, research fellow at the University of Glasgow's School of Physics and Astronomy, who was involved in interpreting the data from the gravitational wave signal. "The addition to the network of a signal from Virgo provided us with a lot of useful data. Having a third detector means that we can now triangulate the position of the source, and much more accurately determine the exact spot in the cosmos where the signal came from."

Being able to both see these events with conventional telescopes and to detect their gravitational waves at the same time would be a huge step forward in astronomy, providing researchers with unprecedented insights into the workings of the universe.