In 1916, Albert Einstein had predicted that in certain circumstances the fabric of the universe itself should wobble and flex. These ripples in the space and time fabric were confirmed hundred years later in 2015 when LIGO, an American observatory, detected waves produced by a pair of colliding massive black holes.

Apart from winning the Nobel, this discovery was the dawn of gravitational wave astronomy. Simply put gravitational waves are to gravity what radio or visible light is to electromagnetism. Traditional astronomy uses electromagnetic radiation from radio waves, gamma rays and visible light to discover the horizons of space. Gravitational waves travel at the speed of light through the universe, unhindered by intervening mass – to gravitational waves the universe is transparent. That is why they can help us explore the darkest corners of the universe

In June this year, scientists have declared the tentative detection of new ultra-low frequency gravitational waves in the universe. It is believed that all galaxies, including our Milky way, have a supermassive black hole at the centre. The waves are thought to be emitted when two supermassive black holes come close to each other when galaxies collide or merge. It is the pairing of binary black holes that produces the music in the universe that has now been captured.

This discovery has generated excitement and anticipation in the scientific community, as well as in those interested in the secrets of the universe. It opens up new avenues for exploration, giving us a chance to learn more about black holes, and how galaxies evolve. At the beginning of its first 380,000 years of life the universe is believed to have been so hot and dense, that it was opaque to electromagnetic radiation. There is now hope that gravitational waves will provide a glimpse of the start of the universe.

This collaborative discovery is also exciting because it is based not on special detectors like LIGO, but on years of tracking pulsars. Pulsars are spinning stars that emit flashes of light with regularity. If a gravitational wave distorts the space time between the pulsar and Earth, then the timing of the pulses would change. Studying these patterns, a hum in the universe has been detected – caused by a constant background of gravitational waves coming from all directions, like ripples in a pond during a downpour.

India has participated and been part of this exciting scientific collaboration. Nearly 37 Indian scientists had participated in the LIGO experiments. In the recent discovery of the cosmic hum, data collected by the Giant Metrewave Radio Telescope near Pune and Indian astrophysicists has played an important part. Already in April 2023, the cabinet approved the LIGO India project to build an advanced gravitational-wave detector in Hingoli district of Maharashtra at an estimated cost of Rs 2,600 crore. The facility is expected to be completed by 2030.

Gravitational astronomy is being seen as the new doorway to peep into the secrets of black holes and the universe. Already, NASA together with other agencies is working towards the launch of the Laser Interferometer Space Antenna (LISA) in the mid-2030s. LISA consists of three spacecraft designed to detect gravitational waves from space. It is another collaborative scientific endeavor of humanity, proving once again that together there is no frontier that humans cannot conquer.

Published in Hindi in the Dainik Bhaskar on 1-8-2023