# Three-detector observation of gravitational waves from a binary black hole coalescence

Congratulations to the LIGO-Virgo collaboration on the 4th detection of gravitational waves! The source of this detection is again merging black holes. This one is special as it is the first time the Virgo collaboration has joined the detection. Having a third detector results in substantially better sky localization (down from ~1000 deg^2 to ~100 deg^2) and the ability to test the polarization states of the incoming waves.

Information on the detection and the detection announcement paper can be found at http://www.ligo.org/detections/GW170814.php. Mark Hannam also has a nice blog post about the event.