In a significant development, an international team of astronomers, which included researchers from seven Indian institutes, has for the first time detected the low-pitched “hum” of gravitational waves propagating throughout the cosmos. Albert Einstein predicted that such waves would exist.
One of the six most sensitive radio telescopes in the world, India’s upgraded Giant Metrewave Radio Telescope (uGMRT) in Pune, was essential in the discovery of the enduring hum. It is believed that the merger of two super-massive black holes in the early cosmos, not long after the Big Bang, is where the gravitational waves (GW) first appeared. Scientists anticipate that this finding will help them understand more about the nature of physical reality and provide light on the nature of merging super-massive black holes and what causes them to collide.
The discoveries were made after 15 years of observations by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), which included more than 190 researchers, including those from the Indian Pulsar Timing Array (InPTA), which used uGMRT. The results were published in a series of papers in The Astrophysical Journal Letters on Thursday. The Indian telescope was used to gather, correct, and improve the signal’s accuracy so that it could confirm the universe’s “hum,” which was discovered by its European counterparts.
The pulsar timing array experiment’s initial run began in 2002, and InPTA joined in 2016. Researchers from NCRA (Pune), TIFR (Mumbai), IIT (Roorkee), IISER (Bhopal), IIT (Hyderabad), IMSc (Chennai), and RRI (Bengaluru) are participating in the InPTA experiment alongside their Japanese counterparts from Kumamoto University.
Einstein first postulated gravitational waves in 1916, but they weren’t actually discovered until the National Science Foundation-funded LIGO in 2016 picked up the waves from a pair of far-off merging black holes. However, compared to what NANOGrav recorded, LIGO observed gravitational waves that were significantly more frequent.
“According to Einstein’s theory, gravitational waves change the arrival times of these radio flashes and thereby affect the measured ticks of pulsars, which are also known as our cosmic clocks,” said Bhal Chandra Joshi of NCRA-TIFR, Pune, who formed the InPTA collaboration throughout the past ten years. But until recently, no one had noticed this alteration. Because of how minute these changes are, astronomers need sensitive telescopes, such as the improved GMRT, and a group of radio pulsars to distinguish them from other disturbances. It takes decades to search for these elusive nano-hertz gravitational waves due to the signal’s sluggish fluctuation.
The pulsar timing array experiment’s initial run began in 2002, and InPTA joined in 2016. Researchers from NCRA (Pune), TIFR (Mumbai), IIT (Roorkee), IISER (Bhopal), IIT (Hyderabad), IMSc (Chennai), and RRI (Bengaluru) are participating in the InPTA experiment alongside their Japanese counterparts from Kumamoto University.
Mayuresh Surnis, an assistant professor at the Indian Institute of Science Education and Research in Bhopal, explained the incident as follows: “If you convert the GW to sound, the background noticed may be dubbed a hum. The background is created by superimposing the GW from many supermassive black hole binary sources. We will be able to determine what kind of blackholes they were after further data analysis. While LIGO detected the GW at high frequency, we did so at low frequency. Therefore, we are looking for the complete GWaves spectrum.
It is wonderful to see our uGMRT data being used for ongoing global work on gravitational wave astronomy, said Yashwant Gupta, centre director at the National Centre for Radio Astrophysics (NCRA), Pune. Researchers from the European PTA and their Indo-Japanese colleagues from the InPTA have published detailed findings from the analysis of pulsar data gathered over 25 years with six of the greatest radio telescopes in the world. This comprises more than three years’ worth of extremely sensitive data gathered with the help of India’s largest radio telescope, the uGMRT, and its adaptability in the rare low radio frequency band.
The signal from pulsars (dead stars), which we are attempting to extract, is extremely feeble, he continued. When the signal travels through the medium of a galaxy, it becomes warped. A low-frequency telescope like the GMRT is necessary to rectify this signal. The precision of the signal improves after signal cleaning, assisting scientists using GMRT to identify the low-frequency gravitational waves that are responsible for it.
