LIGO detects binary black hole merger

The Laser Interferometer Gravitational-Wave Observatory (LIGO) has just announced the detection of a binary black hole merger. This is similar to the black hole merger announced in February 2016 which confirmed that Einstein's General Theory of Relativity was correct. It is the second major event observed since the Advanced LIGO started operations in September 2015.

In both cases, Indian scientists of the Indian Initiative for Gravitational-Wave Observatory (the IndIGO Consortium) made big contributions. A total of 39 Indian scientists from nine different institutions contributed to the detection.

The signals were picked up at the two American LIGO facilities on December 26, 2015. Follow up data was generated by the Cadmium Zinc Telluride Imager (CZTI) on the Indian astronomy satellite, AstroSat. The CZT takes X-ray images and it can also detect gamma radiation.

The American LIGO detectors identified two black holes merging at 1.4 billion light years distance. (A light year is the distance travelled by light in one year. Light travels at 300,000 km per second and gravity waves travel at the same speed.) One hole had a mass 14x times that of the sun, and the other, a mass of 8x solar. The two holes merged into one hole, with a mass of 21x solar and released 1x solar mass worth of energy. The merger signal lasted a second.

This event took place 1.4 billion years ago. it was much smaller than the first black hole merger where the combined mass was 65x solar. The signals were weaker and required smart data analysis to isolate from "noise". The scientists used a technique of matched filtering, which finds signals of a known shape.

A team led by Dr Bala Iyer has solved Einstein's equations to work out the shape of gravitational wave signals for a black hole merger. The foundational work for the matched filtering technique was done 25 years ago, at the IUCAA ( Inter-University Centre for Astronomy and Astrophysics) by Dr Sanjeev Dhurandhar. Scientists from the International Centre for Theoretical Sciences (ICTS) of the Tata Institute of Fundamental Research (TIFR) and the IUCAA, also contributed to estimations of mass, size, spin, etc., of the black holes.

LIGO has made two big strikes within a few months. It will double its range this autumn. IndIGO is building a third LIGO facility in India and this will further improve range and accuracy. Italy and Japan will soon have facilities too. A space-based detector is also planned. Further fundamental advances are eagerly awaited by the scientific community as more gravitational detection facilities become operational.