IITGN team contributes to LIGO discovery of heaviest binary neutron star system

The team of IITGN researchers provided a highly optimized template bank for both online and offline search pipelines, a key component which lead to this discovery. A template bank is a grid of theoretical signal shapes against which noisy data is matched, so as to reliably extract faint signals which may lie buried therein. The challenge was to create the smallest footprint in terms of bank size, while making sure that there was adequate coverage to astrophysical signals and that no “holes” were left in the search space. The team drew inspiration from Lord Kelvin’s famous “sphere-covering” problem to map the task at hand to its geometrical analogue.

“The discovery of systems like GW190425 poses new challenges in astrophysics. It would steer the attention of researchers to find new formation channels of such unusual systems. Science is exciting because of the unknowns that you stumble upon, and here is a big one,” Prof Sengupta said. “I am elated that my students made a critical contribution to this discovery. It is satisfying (to know) that undergraduate students can make cutting edge scientific contributions through collaborative research.”

Expressing joy, Soumen Roy said, “I am excited to see my work featured in the recent detection of the gravitational-wave signal from the merger of the most massive binary neutron star system. I was involved in every aspect of developing and testing the optimized template placement algorithm that was used in the LIGO search pipelines.” He would like to devise new tests of Einstein’s theory of general relativity in the future, he added.

Equally delighted, Nilay Thakor said, “It is inspiring to see an undergraduate research project to be featured in the detection of neutron star collision. It is very encouraging for my further work, as it was my first publication. In future, I am interested in examining what role artificial intelligence could play in improving the detection of gravitational waves.”

Soumen Roy is finishing his PhD thesis at IITGN and preparing for a stint as a postdoctoral researcher. Nilay Thakor is now an MS student in Applied Math and Statistics at Johns Hopkins University, USA.

About the discovery

Neutron stars are the remnants of dying stars that undergo catastrophic explosions as they collapse at the end of their lives. When two neutron stars spiral together, they undergo a violent merger that sends gravitational shudders through the fabric of space and time.

On April 25, 2019, at 1:48 pm Indian Standard Time (IST), the network of advanced LIGO gravitational-wave (GW) detectors in the USA and the Advanced Virgo detector in Italy, detected a signal named GW190425. This was the second observation of a gravitational-wave signal consistent with the merger of a binary neutron star system. This system is notable for having a total mass exceeding that of known galactic neutron star binaries. It is also the first confirmed gravitational-wave detection based on data from a single observatory.

The observation that took place in August, 2017, made history of both gravitational waves and light being detected from the same cosmic event for the first time. An April 25 merger, by contrast, did not result in any light being detected.

However, through an analysis of the gravitational-wave data alone, researchers in the LIGO Scientific Collaboration have learned that the collision produced an object with an unusually high mass. Apart from its massive weight (as far as Binary Neutron Star systems go), the discovery of GW190425 suggests that there is a new population of binary neutron star systems with sub-hour orbital periods, which are not detectable by current electromagnetic surveys.