LIGO and Virgo Announce Four New Gravitational-Wave Detections

The National Science Foundation’s LIGO (Laser Interferometer Gravitational-Wave Observatory) and the European-based Virgo gravitational-wave detector have detected four new black hole merger events. The findings were presented at the Gravitational Wave Physics and Astronomy Workshop in College Park, Md., Dec. 1, 2018. The LIGO and Virgo collaborations have now detected gravitational waves from 10 stellar-mass binary black hole mergers and one merger of neutron stars.

LIGO and Virgo have detected four new gravitational waves. Courtesy of the Virgo website at www.virgo-gw.eu.

The new events are known as GW170729, GW170809, GW170818, and GW170823, in reference to the dates they were detected. Some of the new events broke records. For example, the new event 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.

GW170814 was the first binary black hole merger measured by the three-detector network, and allowed for the first tests of gravitational-wave polarization (analogous to light polarization).

The event GW170817 represented the first time that gravitational waves were ever observed from the merger of a binary neutron star system. This collision was seen in gravitational waves and light, marking a new chapter in multimessenger astronomy, in which cosmic objects are observed simultaneously in different forms of radiation.

“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 Denise Caldwell, director of the National Science Foundation’s Division of Physics.

The next observing run, starting in spring 2019, should yield many more gravitational-wave candidates, said David Shoemaker, spokesperson for the LIGO Scientific Collaboration and senior research scientist at MIT.

The pointing capability of the LIGO-Virgo network was improved by exploiting the time delays of the signal arrival at the different sites and the so-called antenna patterns of the interferometers. The enhanced pointing precision could help speed the identification of other cosmic messengers emitted by the gravitational-wave sources.

Caltech’s Albert Lazzarini, deputy director of the LIGO Laboratory, said, “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.”

LIGO is funded by the National Science Foundation (NSF) and operated by California Institute of Technology (Caltech) and Massachusetts Institute of Technology (MIT). The Virgo collaboration consists of more than 300 physicists and engineers belonging to 28 different European research groups.

The scientific papers describing the new findings, which are being initially published on the arXiv repository of electronic preprints, present detailed information in the form of a catalog. Paper: “GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs” (https://arxiv.org/abs/1811.12907). Paper: “Binary Black Hole Population Properties Inferred from the First and Second Observing Runs of Advanced LIGO and Advanced Virgo” (https://arxiv.org/abs/1811.12940). Papers are available at arXiv (https://arxiv.org/abs/1811.12907) and LIGO DCC (https://dcc.ligo.org/).