Editorial: Cosmic choir

The recent discovery of the cosmic background hum is one such revelation that evokes both a sense of wonder and existential dread

If one ponders over the vastness of the universe and the scale of celestial events, it would lead to an inevitable realisation that all of human existence is barely a flicker in the grand cosmic spectacle and that all of our collective experiences — dreams and despair, joys and worries — seem pointless, after all. The recent discovery of the cosmic background hum— a low-frequency choir reverberating across the universe — is one such revelation that evokes both a sense of wonder and existential dread; awe-inspiring because the breakthrough marks the beginning of a whole new way to observe the universe and dread-inducing because the moments such as these raise questions over the insignificance of human existence in the cosmic scheme of things. Over a century after Albert Einstein predicted the existence of gravitational waves — the ripples in space-time caused by collision of black holes — scientists have now ‘heard’ them. Some have described it as the ‘song of the stars’ and ‘cosmic orchestra’. These gravitational waves are the collective echo of supermassive black holes — thousands of them, some as massive as a billion suns, sitting at the hearts of ancient galaxies up to 10 billion light-years away — as they slowly merge and generate ripples in space-time. After years of coordinated research under the banner International Pulsar Timing Array consortium, scientists from across the world, including India, have picked up the background hum of the universe from the gravitational waves that originated billions of years ago.

It is revealed that the universe is awash with gravitational waves, the ripples in the fabric of the universe that bend and stretch the space-time as they travel through everything at the speed of light almost entirely unimpeded. To detect these low-frequency waves, astronomers focused on pulsars, the remnants of dead stars that exploded in supernovae. Pulsars emit regular beams of radio waves at precise intervals, akin to cosmic lighthouses, making them incredibly accurate clocks. By observing 115 pulsars throughout the Milky Way, researchers measured minuscule differences in their timing, searching for subtle indications of gravitational waves. In all, six of the world’s most powerful and large radio telescopes, including Metrewave Radio Telescope (GMRT) at Pune-based National Centre for Radio Astrophysics (NCRA), were deployed to study 25 pulsars over a period of 15 years. The monumental breakthrough is celebrated as a transformative milestone uncovering cosmic secrets. The breakthrough shatters the perception of a static universe and reveals a rolling, noisy universe alive with the cosmic symphony of gravitational waves. It’s like a choir, with all these supermassive black hole pairs chiming in at different frequencies. As more data is gathered, this cosmic hum could help researchers gain further insights into the early expansion of the universe and shed light on the enigma of dark matter and dark energy, the mysterious stuff that makes up the bulk of the universe.

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