The twin LIGO (Laser Interferometer Gravitational-Wave Observatory) detectors, located in Livingston, Louisiana, and Hanford, Washington, and the Virgo detector located near Pisa, Italy, have detected four new gravitational waves — ripples in the fabric of spacetime.

Gravitational waves carry information about their origins and about the nature of gravity that cannot otherwise be obtained.

During a two-year span, physicists on the LIGO and Virgo teams detected gravitational waves from 10 black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions.

The four new observations — named GW170729, GW170809, GW170818 and GW170823 for the dates they were detected — include some record breakers.

One of the new events, GW170729, is the most massive and distant gravitational-wave source ever observed. In this coalescence, which happened roughly 5 billion years ago, an equivalent energy of almost five solar masses was converted into gravitational radiation.

The GW170818 event, which was detected by the global network formed by the LIGO and Virgo observatories, was very precisely pinpointed in the sky.

The position of the binary black holes, located 2.5 billion light-years from Earth, was identified in the sky with a precision of 39 square degrees. That makes it the next best localized gravitational-wave source after the GW170817 neutron star merger.

Two scientific papers describing the new results are published on arXiv.org and include a catalog of all gravitational wave detections and candidate events observed to date.

“The release of four additional binary black hole mergers further informs us of the nature of the population of these binary systems in the universe and better constrains the event rate for these types of events,” said Dr. Albert Lazzarini, Deputy Director of the LIGO Laboratory and researcher at Caltech.

“In just one year, LIGO and VIRGO working together have dramatically advanced gravitational-wave science, and the rate of discovery suggests the most spectacular findings are yet to come,” said Dr. Denise Caldwell, Director of NSF’s Division of Physics.

“The accomplishments of NSF’s LIGO and its international partners are a source of pride for the agency, and we expect even greater advances as LIGO’s sensitivity becomes better and better in the coming year.”

“The new catalog is another proof of the exemplary international collaboration of the gravitational wave community and an asset for the forthcoming runs and upgrades,” said EGO Director Dr. Stavros Katsanevas.

“The next observing run, starting in spring 2019, should yield many more gravitational-wave candidates, and the science the community can accomplish will grow accordingly. It’s an incredibly exciting time,” said Dr. David Shoemaker, spokesperson for the LIGO Scientific Collaboration and senior research scientist in MIT’s Kavli Institute for Astrophysics and Space Research.

“It is gratifying to see the new capabilities that become available through the addition of Advanced Virgo to the global network,” said Virgo Collaboration spokesperson Dr. Jo van den Brand, a scientist at Nikhef (the Dutch National Institute for Subatomic Physics) and VU University Amsterdam.

“Our greatly improved pointing precision will allow astronomers to rapidly find any other cosmic messengers emitted by the gravitational-wave sources.”

“These new discoveries were only made possible through the tireless and carefully coordinated work of the detector commissioners at all three observatories, and the scientists around the world responsible for data quality and cleaning, searching for buried signals, and parameter estimation for each candidate — each a scientific specialty requiring enormous expertise and experience,” said Dr. Laura Cadonati, deputy spokesperson for the LIGO Scientific Collaboration.

“These results mark an evolution in the way we are thinking about binary black hole mergers detected by LIGO and Virgo,” said Professor Peter Shawhan, from the University of Maryland.

“State-of-the-art waveform models, advanced data processing and better calibration of the instruments have allowed us to infer astrophysical parameters of previously announced events more accurately and discover four new gravitational wave transients from black hole mergers,” said Professor Alessandra Buonanno, a researcher at the University of Maryland and director at the Max Planck Institute for Gravitational Physics in Potsdam, Germany.

“I look forward to the next observing run in spring 2019, where we expect to detect more than two black hole mergers per month of collected data.”

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LIGO Scientific Collaboration & Virgo Collaboration. 2018. GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs. arXiv: 1811.12907

LIGO Scientific Collaboration & Virgo Collaboration. 2018. Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo. arXiv: 1811.12940