Scientists announced Wednesday they have detected a fourth gravitational wave signal coming from the merger of two black holes.
It's the first time this phenomenon has been measured simultaneously by both the U.S.-based LIGO and Italy-based Virgo detectors.
Originally predicted in the early 20th century by Albert Einstein, gravitational waves -- ripples in space and time -- were not detected until 2015, when the Laser Interferometer Gravitational-wave Observatory (LIGO) identified the first such signal from two merging black holes.
LIGO's two detectors, located in Livingston, Louisiana, and Hanford, Washington, later detected two other similar events.
The latest observation was made on August 14, 2017, at 10:30:43 GMT. It's the first gravitational wave signal recorded by the Virgo detector.
"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," France Cordova, director of the U.S. National Science Foundation, which funded the LIGO project, said in a statement.
"This is an exciting milestone in the growing international scientific effort to unlock the extraordinary mysteries of our universe," Cordova said.
The detected gravitational waves were emitted during the final moments of the merger of two black holes with masses about 31 and 25 times the mass of the Sun and located about 1.8 billion light-years away, researchers said.
The newly produced spinning black hole has about 53 times the mass of our Sun, which means that about three solar masses were converted into gravitational-wave energy during the coalescence, they said.
A paper about the event has been accepted for publication in the journal Physical Review Letters.
The Virgo collaboration, which joined in the LIGO's observation on August 1, consists of more than 280 physicists and engineers belonging to 20 different European research groups.
"It is wonderful to see a first gravitational-wave signal in our brand new Advanced Virgo detector only two weeks after it officially started taking data," said Jo van den Brand of Nikhef, spokesperson of the Virgo collaboration.
"This is just the beginning of observations with the network enabled by Virgo and LIGO working together," said MIT's David Shoemaker, spokesperson of the LIGO Scientific Collaboration. "With the next observing run planned for Fall 2018 we can expect such detections weekly or even more often."