A scientific collaboration that began decades ago to detect gravitational waves
The researchers said they were able to confirm a "burst of gravitational waves" that occurred when two black holes merged approximately 1.3 billion years ago, around the time when multicellular life was first beginning on Earth.
"Ladies and gentlemen we have detected gravitational waves," said David Reitze, one of the scientists making the announcement. "We did it. I am so pleased to be able to tell you that."
The existence of gravitational waves was put forth in theory 100 years ago by Albert Einstein. The 1993 Nobel Prize in Physics was awarded for showing it would be possible to measure them, and Thursday's announcement took the work to the next step, showing that they had been detected and measured.
Reitze was joined at a packed news conference in Washington by scientists from the Massachusetts Institute of Technology (MIT) and one of the sponsoring organizations, the US National Science Foundation.
Reitze said the detection was made almost simultaneously at two observatories in the United States on September 14 and lasted just 0.2 seconds.
The observatories are part of the Laser Interferometer Gravitational-Wave Observatory (LIGO) system and are located on opposite ends of the United States - one in Louisiana and one in Washington state.
It was very clear and there was no room for doubt that it was direct evidence of the waves, said Bruce Allen, who is acting director at Germany's Max Planck Institute for Gravitational Physics.
Allen said two scientists with his group in the northern German city of Hanover were the first to notice the effect.
It took months of careful checking and rechecking to make sure that what was detected was gravitational waves, Reitze said, adding that none of the physicists involved in Thursday's announcement had any doubt of what LIGO heard. The American Physical Society published a paper detailing the event and released it to the public the moment the news conference began.
There were immediate suggestions that the discovery could well win the collaborators the Nobel Prize in Physics.
According to Einstein's theory, gravitational waves move at the speed of light in a vacuum and bend space. Each accelerated body, therefore, sends gravitational waves, which increase in strength the greater the mass and the faster it moves.
The scientists participating in the news conference said the detection of gravitational waves "opened a window on the universe" into which they could explore more questions posed by astrophysicists.
"Each time a window has been opened up there have been surprises," said Kip Thorne of Caltech. "We will see big surprises."