LIGO Hanford scientists celebrate while looking ahead to future discoveries

The announcement of the detection of gravitational waves elicited jubilation from the scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) in Hanford, Washington, one of the two detectors to receive the first signal.

LIGO Hanford and LIGO Livingston (Louisiana) detected the event on 14 September 2015, at 02:51 Pacific Time (09:51 UTC). About three minutes later, according to LIGO Hanford head Frederick Raab, "one of our computer codes said ‘Hey, look at this!'"

The first observing run of "Advanced LIGO" had not even officially begun after the instrument's five-year upgrade, and Hanford LIGO lead scientist Michael Landry figured the signal was just a test, called an injection. When he arrived at work that morning he asked if LIGO was in an injection phase, and was told it was not.

"At that point it became a serious thing," Landry said.

The signal came from a source that was "roughly" in the southern hemisphere sky, said Raab. "The Louisiana people tell me I have to say they got it first," 7 milliseconds earlier than Hanford. That began months of cross-checking and verifying data to make sure that the detection was from a real event.

"It's a gradual process of becoming more and more confident with it," said Landry. "Extraordinary claims require extraordinary proof, and the extraordinary proof was months and months of analysis."

While the scientists' confidence in the detector was high, they still didn't know what was out there.

"We knew that these signals would be big, we knew that you could see them very, very far away, but we didn't know the sources actually existed that would produce them - and so, now we know," Raab said. "That totally revolutionizes our expectations of what we can see."

Raab says they are now "feverishly" working on tuning the detectors up for LIGO's second observing run, to begin later this year. He says the next run will represent "a significant boost in sensitivity, where we expect we might be seeing events like this several times a month."