The first run yielded only three events and the second run found eight. Unlike the first two runs, the recent third observing run was split into two parts. The first half stretched from April 2019 to October 2019. Since their initial 2015 detection, LIGO/Virgo detected a grand total of 50 gravitational wave events. Of those signals, 39 are new binary black hole or neutron star collisions that have not been previously announced. That’s more than three times the number of events detected in the first two runs combined.
There are two main causes for the abundance of signals during the most recent observing run. First, the LIGO/Virgo instruments received significant improvements, which the team estimates resulted in a 60 percent improvement in the detectors’ sensitivity. On top of that, the observatories were able to operate longer without interruption, increasing the chances of picking up a signal.
With so many new signals — 50 in total, counting previous detections — astronomers have a multitude of data to tackle when it comes to black holes and neutron stars. “We’ve learned more about what nature permits,” said LIGO collaboration member Richard O’Shaughnessy in a press release. “We found more big black holes, smaller siblings of the massive event described in the summer and we found, too, that large black holes can be rapidly spinning.” With so many questions still left unanswered about these exotic objects, O’Shaughnessy suspects even more discoveries are on the horizon.
And LIGO/Virgo won’t be finished reporting new gravitational wave signals anytime soon. Results from the second half of the third run are currently being analyzed, and a fourth run is planned to begin in mid-2022. That run will also include the Kamioka Gravitational Wave Detector (KAGRA) in Japan.