The universe has been singing to scientists — the sounds generated by the merging of supermassive black holes, a phenomenon almost unimaginable on the human scale, have been described as the “cosmic bass notes” of gravitational waves.
India’s Giant Metrewave Radio Telescope (GMRT) was one of the world’s six large telescopes that played a key role in finding the first direct evidence for the relentless vibrations of the fabric of the universe, caused by the ultra-low frequency gravitational waves.
Reporting on the discovery, The Guardian said that this promised to “open a new window on the monster black holes lying at the centres of galaxies”.
The National Aeronautics and Space Administration (NASA), the independent agency of the United States of America federal government, describes black holes as “a place in space where gravity pulls so much that even light cannot get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying.”
Tracking the cosmic mergers of such black holes has brought scientists this gift of a long gravitational wave. The findings have been presented in papers published yesterday in the Astrophysical Journal Letters. “This is huge news,” said Dr Stephen Taylor, Chair of the North American Nanohertz Observatory for Gravitational Waves (Nanograv) consortium and astrophysicist at Vanderbilt University in Nashville, US.
Dr Michael Keith, a scientist from at Jodrell Bank Centre for Astrophysics, Manchester, the United Kingdom, was involved in the project. He said, “We are incredibly excited that after decades of work by hundreds of astronomers and physicists around the world, we are finally seeing the signature of gravitational waves from the distant universe.”
Sounds from gravitational waves have been captured before, but they were barely there. In the current discovery, the scientists listened to a deeper frequency range; they tracked one complete wave that took 30 years to reach Earth and was detected by scientific installations here. They believe that the wave was generated not by two individual black holes, but by the merging of many black holes over a period of an estimated 8 billion years.
“We think each pair contributes a little wave, which is added to a little wave of another, and all together that is what we may see right now — a sort of murmur of the entire population,” said Prof Alberto Vecchio of the University of Birmingham and a member of the European Pulsar Timing Array (EPTA).
The global team of scientists included those from the Indian Pulsar Timing Array (InPTA), which used the Pune-based GMRT telescope. “We are within a whisker of achieving such a dynamic range where one can finally listen to the bass sections in this cosmic gravitational-wave-symphony,” said Pratik Tarafdar of The Institute of Mathematical Sciences, Chennai.
“It is fantastic to see our unique uGMRT data being used for the ongoing international efforts on gravitational wave astronomy,” said Yashwant Gupta, Centre Director at National Centre for Radio Astrophysics (NCRA), Pune, which operates the GMRT. The team’s results are considered a crucial milestone in opening a new, astrophysically-rich window in the gravitational wave spectrum.
Scientists of the EPTA, in collaboration with the Indo-Japanese colleagues of the InPTA, arrived at the findings after analysing pulsar data collected over 25 years with six of the world’s largest radio telescopes.
This includes more than three years of very sensitive data collected using the unique low radio frequency range and the flexibility of GMRT, which underwent significant upgrades in 2019.
“The results reported by the EPTA+InPTA collaboration… are the culmination of many years of efforts by many scientists, including early-career researchers and undergraduate students,” said Prof. Shantanu Desai of IIT, Hyderabad.
The InPTA experiment involved researchers from NCRA (Pune), TIFR (Mumbai), IIT (Roorkee), IISER (Bhopal), IIT (Hyderabad), IMSc (Chennai) and RRI (Bengaluru), along with their colleagues from Kumamoto University, Japan.
The 100m Effelsberg radio telescope in Germany; the Lovell Telescope of the Jodrell Bank Observatory in the United Kingdom; the Nancay Radio Telescope in France; the Sardinia Radio Telescope in Italy; and the Westerbork Synthesis Radio Telescope in the Netherlands were used for observations.
—With inputs from the Press Trust of India