In the early morning of Sept. 14, 2015, a new window on the universe opened with the first successful detection of gravitational waves, the incomprehensibly minuscule ripples in space-time from exceptionally violent events — in this case, the in-spiral and collision of two medium-mass black holes, a never-before detected phenomenon.
This breakthrough was achieved by the Laser Interferometer Gravitational-Wave Observatory (LIGO), with detectors in Livingston, Louisiana and Hanford, Washington. These ultra-sensitive instruments had been operating without success since 2002, interrupted periodically for enhancements to boost sensitivity. At long last, the historic first detection occurred mere hours after “Advanced LIGO” had switched on.
ALIGO’s first data run yielded three black hole mergers in 120 days, at a rate of one every 40 days on average. After further enhancements, ALIGO’s next run spanned 268 days, culminating in eight more events (seven black hole mergers and the first-ever neutron star merger), averaging 34 days between detections.
On April 1, with its sensitivity boosted by a further forty percent, ALIGO began its third data run. And, just after noon on Monday, another event was detected. Preliminary analysis suggests a 99 percent probability that it was another black hole merger at a distance of 3.6 to 6 billion light years.
Unlike past events, which were kept under wraps until after they had been thoroughly analyzed, this one was announced immediately, to allow astronomers worldwide to train their telescopes near the eastern border of Andromeda to see if the event is detectable in the electromagnetic spectrum. Back in 2017, such “multi-messenger astronomy” confirmed the hypothesis that most of the universe’s gold (including that in jewelry) was likely created in neutron star mergers.
To keep up with the latest gravitational wave detections, just follow the Twitter handle @LIGO.
Next column: The first image of a black hole.