April and May brought a bounty of gravitational wave detections to the combined LIGO-Virgo network observatories with 13 candidate events recorded. June was mostly quiet for the cosmos – at least, until the very last moment. On June 30, researchers saw a clear detection. Then, just over 24 hours later, another came through.
The June 30 event, also known as S190630ag, is estimated to be a collision between two black holes roughly 3 billion light-years away. This is certainly an impressive distance, but observations earlier in the year were estimated to be three times as far. Still, the chances that S190630ag is a genuine event are good, with an estimated false alarm rate at less than once every 200,000 years.
The issue with this detection is that only two out of three observatories – Virgo and the LIGO in Livingstone – were online at the time. This will make finding a potential visual counterpart difficult as triangulation is not available. Nonetheless, telescopes are looking at those regions to see if there are new sources that weren’t there before.
The July 1 event, S190701ah, also seems to be a black hole merger around 3 billion light-years away. However, that's where the similarities with S190630ag end. It was identified from quite a narrow region in the sky and spotted by all three observatories, with the false alarm rate at just once every 1 year and 7 months. While both detections are going through more detailed analysis, the team is pretty confident the June 30 observation is a real one. We will find out over the next months if the July 1 detection is real or not.
If you, like us, don’t want to miss a gravitational wave detection, there is now an app called Gravitational Wave Events (available on iPhone) that tells you when a new signal is observed. The international scientific community has three observatories at its disposal – two LIGO (Laser Interferometer Gravitational-Wave Observatory), one in Washington State, and the other in Louisiana – which are made of two L-shaped, 4-kilometer-long (2.5-mile) interferometers. And then there’s Virgo, similar in structure but slightly smaller and located in Italy just outside Pisa.