Virgo Joins LIGO in Detection of Gravitational Waves

On September 27, researchers from the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Advanced Virgo Detector announced their joint detection of a gravitational-wave signal from the coalescence of two black holes. The observation by three detectors (two from LIGO and the Virgo detector) allows the teams to improve their ability to identify where in the sky the waves are coming from. The announcement was made at a meeting of the G7 science ministers in Turin, Italy, and a paper describing the detection has been accepted for publication by the APS journal Physical Review Letters.

The signal, which was observed on August 14, 2017, comes from a merger of a black hole 30.5 times the mass of the Sun with another black hole 25.3 times the mass of the Sun. The event occurred 540 megaparsecs from Earth, or about 1.8 billion light years away. Because the gravitational-wave detection network involves three detectors, the researchers have been able to narrow down the location of the signal source by a factor of nearly 20 compared with LIGO’s previous detections.

Each of three detectors, LIGO’s two in Hanford, Washington, and Livingston, Louisiana, and Virgo in Pisa, Italy, recorded the characteristic “chirp” signal of the black holes circling each other, then speeding up and merging. By comparing the waves’ arrival time at each detector, the researchers were able to improve the determination of the source direction. Previous detections by LIGO involved two detectors, which meant that the mergers could only be identified as lying somewhere in large swathes of the sky.

In addition to better localizing the gravitational-wave source, the participation of Virgo means that the polarization of the waves can be studied. Like other kinds of waves, gravitational waves oscillate in specific directions. LIGO’s detectors are oriented in similar ways, so they were unable to sense the oscillation direction. Virgo is oriented in a way complementary to LIGO, so the three detectors can together analyze the wave polarization. With this information, even more stringent tests of general relativity should become possible.

David Voss

David Voss is the Editor of APS News.

This article is reprinted from APS News. A follow up article about the new paper from LIGO and Virgo will appear in Physics after the paper has published in Physical Review Letters.