These Black Holes Merged Nearly Two Billion Years Ago and We Have the Receipts

The newest gravitational wave discovery is the first to involve three detectors.

On Wednesday, representatives of the Virgo and LIGO Scientific Collaborations confirmed weeks of speculation about the possible detection of a new wave, or ripple in spacetime, on August 14. The rumor mill had been brimming about a possible discovery of two merging neutron stars in the galaxy NGC 4993, some 130 million light years from Earth, which would have marked the first time that gravitational waves were captured from a source other than a black hole merger.


In a twist, it turns out that the August 14 event, dubbed GW170814, was generated by a black hole merger, much like the three previous confirmed detections. What sets this event apart is that it marked the first time the newly operational Advanced Virgo detector near Pisa, Italy, captured a wave. The past three waves were detected only by the two US-based detectors in Washington State and Louisiana, operated by the Laser Interferometer Gravitational-Wave Observatory (LIGO).

As with other observational networks, the introduction of more facilities improves the odds of detecting astronomical phenomena, in this case the shadowy traces of disruptive cosmic events. It also allows for improved precision in unpacking their origins.

Virgo has been undergoing a multi-year upgrade to boost its sensitivity, and the new and improved detector finally went online alongside the American detectors on August 1. Within just weeks, it was rewarded with its inaugural detection, while contributing to the first three-detector discovery of a black hole merger.

North arm of the Advanced Virgo detector in Italy. Image: Jérôme Degallaix

"This is just the beginning of observations with the network enabled by Virgo and LIGO working together," said David Shoemaker, spokesman for the LIGO Scientific Collaboration, in a statement. "With the next observing run planned for fall 2018, we can expect such detections weekly or even more often."

The wave was created when two black holes, which were 31 and 25 times more massive than the Sun, collided some 1.8 billion light years away. As they merged into one black hole containing 53 times the mass of the Sun, the remaining three solar masses escaped as gravitational wave energy.


Read More: LIGO's Four Gravitational Wave Detections Come From Off-Kilter Black Hole Mergers

Nearly two billion years after this wave was formed, it passed through Earth, just in time to be flagged by Virgo and LIGO. A paper about the August 14 event has been published in Physical Review Letters in tandem with an announcement made by Virgo and LIGO representatives at the Reggia di Venaria Media Center in Turin, Italy.

Virgo/LIGO announcement in Turin, Italy. Video: University of Florida—Department of Physics

"With this first joint detection by the Advanced LIGO and Virgo detectors, we have taken one step further into the gravitational-wave cosmos," David H. Reitze, executive director of the LIGO Laboratory, commented on the discovery.

"Virgo brings a powerful new capability to detect and better locate gravitational-wave sources, one that will undoubtedly lead to exciting and unanticipated results in the future."

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