LIGO detects a second pair of colliding black holes

15 June, 2016

UIB participated, via the LIGO Scientific Collaboration, in the identification of a second gravitational wave event in the data of the Advanced LIGO detectors.

Some months after the first detection of gravitational waves from the merger of two black holes (GW150914), the Laser Interferometer Gravitational wave Observatory (LIGO) has made another observation of gravitational waves from the collision and merger of a pair of black holes. This signal, called GW151226, arrived at the LIGO detectors on 26th of December 2015 at 03:38:53 UTC. GW151226 is the second confirmed observation of the merger of a binary system and, together with GW150914, marks the beginning of gravitational wave astronomy as a revolutionary new medium to explore new frontiers of our universe.

This signal, GW151226, was identified only 70 seconds after its arrival on Earth by low-latency algorithms, and the first indications for its origin were obtained approximately one minute later. Essential both for the detection and for the posterior analysis was a technique known as matched filtering. In this method, the data is compared to hundreds of thousands of predicted gravitational wave signals ("waveforms") with the goal of finding the best match.

The development of precise waveforms based on General Relativity was indispensable for studying binary black hole mergers, especially for GW151226 with its lower intensity compared to GW150914, making it difficult to see in the data without matched filters. Waveform development is one of the main activities of the Relativity and Gravitation Group (GRG) at the University of the Balearic Islands (UIB), their models being used in the analysis of the LIGO/Virgo data and to conduct this discovery. These models are calibrated to numerical simulations, generated in many cases thanks to the use of European computational infrastructure (PRACE) and the Red Española de Supercomputación. Dr. Sascha Husa, professor at UIB and member of GRG, leads an international PRACE project with more than 8 million CPU hours. Since 2010 the group at UIB has had continuous access to computation time on MareNostrum, the most potent Spanish supercomputer at BSC-CNS.

The next science run of the LIGO detectors in Hanford and Livingston is scheduled for this autumn, and is predicted to have higher sensitivity, resulting in a higher number of detections. Stay tuned!

Science summary (spanish)

Press release (spanish)

UIB press release

LIGO press release

Published in PRL 116, 241103 (2016)