Mumbai: In an international effort to unlock the secrets of the universe, Indian scientists have been using the country’s AstroSat space telescope to search for light signals from some of the most powerful cosmic events—collisions between black holes and neutron stars.Gravitational waves, first detected in 2015, are ripples in space-time caused by such massive collisions. These waves are picked up by a global network of detectors, including LIGO in the United States, Virgo in Europe, and KAGRA in Japan. However, it remains an open question whether these mergers also emit light—such as X-rays—which could give scientists a clearer view of the events.This is where the Indian team comes in. Led by Professor Varun Bhalerao from the Indian Institute of Technology Bombay (IIT-B), researchers used AstroSat’s Cadmium Zinc Telluride Imager (CZTI) to search for X-rays following over 70 gravitational wave events recorded by the global network.“If black hole mergers emit X-rays, it would challenge our current understanding of how these extreme collisions work,” explained Gaurav Waratkar, one of the researchers on the team.The team focused on events involving either two black holes or a black hole and a neutron star. Their search covered distances up to 457 million light-years for neutron star mergers and up to 32 billion light-years for black hole mergers. Despite the thorough search, no X-ray signals were found.But the absence of detection is still a significant result. “It helps us set clear limits on how bright these events could be,” said Waratkar. “We now know they are fainter than what even our best instruments can detect at present.”Professor Bhalerao said, “The universe is the most extreme laboratory of physics. It often surprises us with strange phenomena. By continuing to look for X-ray bursts, we not only test our knowledge but also open doors to new theories.”Looking ahead, India’s involvement in this global science mission is set to deepen. When LIGO-India becomes operational and the upcoming Daksha satellite is launched, scientists will have even more advanced tools to detect light from distant gravitational wave events. Daksha, designed with ultra-sensitive X-ray detectors, aims to monitor the entire sky and spot even faint flashes of light from cosmic mergers.The current observation run of the global GW detectors is expected to conclude in October 2025, potentially adding many more events for researchers around the world—including India—to explore.