A fourth gravitational wave has been detected-this time with help from Italy-based equipment-after two black holes collided, sending ripples through the fabric of space and time, researchers said Wednesday.

Gravitational waves were predicted by Albert Einstein a century ago as part of his theory of general relativity, but the first hard evidence of their existence came only in 2015, when two US detectors found the first such signal.

The latest space-time ripples were detected on August 14 at 10:30 GMT when two giant black holes with masses about 31 and 25 times the mass of the Sun merged about 1.8 billion light-years away.

“The newly produced spinning black hole has about 53 times the mass of our Sun,” said a statement from the international scientists at Virgo detector, located at the European Gravitational Observatory (EGO) in Cascina, near Pisa, Italy.

“While this new event is of astrophysical relevance, its detection comes with an additional asset: this is the first significant gravitational wave signal recorded by the Virgo detector.”

The Virgo detector-an underground L-shaped instrument that tracks gravitational waves using the physics of laser light and space-recently underwent an upgrade, and while still less sensitive than its US counterparts, it was able to confirm the same signal.

Known as interferometers, these high-tech underground stations do not rely on light in the sky like a telescope does, but instead sense vibrations in space and can pick up the “chirp” created by a gravitational wave.