On August 17, two gravitational wave detectors in the US detected a neutron star merger 130 million light years away, while the European detector called Virgo did not see anything. Far from being a problem, it led scientists to exclude vast regions of the sky and focus on a small portion to search for where it had come from.Merging neutron stars emit light and gamma rays. Back in India , the satellite Astrosat didn’t pick it up either. This led Indian scientists to pinpoint the source by inferring that it was on the side of sky obscured by the Earth. The Icecube observatory in Antarctica picked up six neutrino emissions at the same time, and India’s optical telescope at Hanle confirmed that they were not related to the neutron star merger.India’s Giant Meter Wave Radio Telescope (GMRT) also did not pick up radio waves from the source, giving astronomers further clues to the nature of the neutron stars.“It is a coincidence that all Indian instruments contributed through exclusion,” said Arun Bhalerao, assistant professor at IIT Bombay’s physics department. “The merger of the neutron stars was announced yesterday (Monday) in the US, and is one of the most important scientific discoveries in a long time.”The Laser Interferometer Gravitational Wave Observatory (LIGO) in the US made the first detection of gravitational waves in February last year. These were created by the union of two massive black holes . Since then, it had detected two more such mergers.August 17 marked the first observation of such a phenomenon between neutron stars. It was also the first observation of an event through multiple means — gravitational waves, gamma rays, and visible light.Black holes and neutron stars are remnants of dead stars; the more massive ones end up as black holes. Black holes are just a mass of spinning objects with no information coming out of them. Neutron stars are not like that. “Black holes are boring after you have seen a few,” said CS Unnikrishnan , professor at the department of high energy physics at the Tata Institute of Fundamental Research (TIFR). “But neutron stars are rich in detail.”The study of neutron stars can provide interesting insights into the laws of physics and the nature of the universe.One such insight could be how fast space is expanding at the location where the celestial event occurred, which in turn could yield more information on the nature of the expansion of the universe.Many Indian scientists were part of the gravitational wave detection. Two major contributions have come from Sanjeev Dhurandhar of the Inter-University Centre for Astronomy and Astrophysics in Pune and Bala Iyer, currently at the International Centre for Theoretical Sciences (ICTS) in Bengaluru. Dhurandhar worked out ways of separating signals from the noise. Iyer computed the gravitational wave forms that could come from mergers of black holes and neutron stars, and these computations formed the basis of the templates for the LIGO and European detectors.The detection of gravitational waves has produced a burst of activity around the world as nations such as Australia, the Netherlands and the UK have increased investment in gravitational astronomy China , which has so far not paid much attention to it, is also reportedly eyeing the area keenly. It’s not been part of LIGO so far.