The gravitational wave detection was “the first time, a chance event; second time, a coincidence, and third, a pattern,” says Bangalore Sathyaprakash, a senior scientist with the LIGO collaboration.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in the U.S. have detected yet another merger of two black holes on January 4, 2017. Named GW170104, this signal marks the third confirmed detection of gravitational waves coming from a binary black hole merger. It is of great interest to the scientific community that the black holes, having masses nearly 31 times and 19 times the sun’s. Until the first detection of gravitational waves by LIGO in 2015 (GW150914) it was not known that such massive black holes could exist.

The gravitational wave detection was “the first time, a chance event; second time, a coincidence, and third, a pattern,” says Bangalore Sathyaprakash, a senior scientist with the LIGO collaboration in the U.S. and an editor of the paper describing these results which was published in Physical Review Letters.

India’s ASTROSAT mission did a related sensitive search for short duration x-ray flashes associated with the event and did not detect any. These results will be published soon by the scientists from ASTROSAT.

Meanwhile, at LIGO, this time around, the detection has revealed not merely a black hole merger, but also the alignment of the spins of the black holes. This can shed light on the way the black holes might have formed. In this event, the spins of the individual black holes making up the merger are probably not aligned along the same direction. This supports the theory which says that black holes form independently in a star cluster, then sink to the centre of the cluster and eventually merge.

Also read: Second breakthrough for LIGO gravitational wave detectors

The U.S.-based Laser Interferometer Gravitational-Wave Observatory has discovered a new population of black holes with masses that are larger than what had been seen before with X-ray studies alone (purple). The three confirmed detections by LIGO (GW150914, GW151226, GW170104), and one lower-confidence detection (LVT151012), point to a population of stellar-mass binary black holes that, once merged, are larger than 20 solar masses — larger than what was known before. Image: LIGO/Caltech/Sonoma State (Aurore Simonnet)

Simultaneously, the detection does not favour the competing theory according to which binary black holes form in pairs even at the start and eventually merge. The latter theory prefers that the pair of black holes will both have to have aligned spins.

Yet another aspect of the observation is that it yields support to Einstein’s General Theory of Relativity. According to this theory, gravitational waves, unlike light waves, will not disperse as they travel through space. This too has been confirmed by the analysis of the presently detected signal.

One drawback of having just the two detectors at Hanford, Washington and Livingston, Louisiana tuned to detect gravitational waves is that they cannot accurately figure out where in the sky the signal is coming from. Just as in the case of a GPS, they need at least three non-collinear detectors to do this. Of course, a network of detectors will improve the scope of “Gravitational Wave Astronomy,” the era of which has just been ushered in by the third detection of gravitational waves from a binary black hole merger. The Italy-based VIRGO detector is almost in place and will join in to collect data later in 2017, a spokesperson for VIRGO said, at a tele-conference organised by LIGO collaboration.

An aerial photo shows Laser Interferometer Gravitational-wave Observatory Livingston Laboratory detector site near Livingston, Louisiana. The twin detectors, a system of two identical detectors constructed to detect incredibly tiny vibrations from passing gravitational waves, are located in Livingston and Hanford, Washington. File | Photo Credit: Reuters

The study had a major Indian contribution and the LIGO-India facility, which is making immense progress will join the club in 2024.