For the first time, scientists have “heard” the sound of gravitational waves produced by the slow-motion merger of supermassive black holes, in what has been hailed as a landmark finding. On Wednesday, the worldwide research team, which included astrophysicists from India, captured gravitational waves rippling through space-time. They are allegedly the most potent things ever measured.
Researchers from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), who have been closely watching stars known as pulsars that serve as cosmic metronomes, discovered the finding. A century ago, Albert Einstein made the initial prediction of gravitational waves, but it wasn’t until 2016 that this prediction was confirmed when the US-based Laser Interferometer Gravitational-Wave Observatory (Ligo) discovered the merger of two black holes proving that space itself can be stretched and squeezed.
“We’ve opened a new window of observation on the universe”
Since the 1970s, when they were first discovered, scientists had only found hints of their existence. Additionally, the wave identified in 2023 differs significantly from the one detected in 2016, when scientists were only able to record brief “chirps” of gravitational waves connected to the mergers of black holes or neutron stars that were only a little bigger than the sun. “We’ve opened a new window of observation on the universe,” said Chiara Mingarelli, an astronomer and assistant professor at Yale University in the US and a member of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) team.
The new type of gravitational waves is likened by Mingarelli to a “choir,” with the pairings of supermassive black holes ringing in at various frequencies. Along with it, she stated that the gravitational wave background was “about twice as loud as I’d expected”. The new study relied heavily on objects known as pulsars, which are the incredibly dense cores of shattered stars that spin at the rate of kitchen blenders. It took over 70 pulsars to get the data.
“As gravitational waves pass through the galaxy, they stretch and they squeeze it. And then the times of arrival of these pulses are changed. So one pulsar, as it’s approaching the earth, its pulses will arrive a little earlier than we expect, as other pulsars will be away from the earth because it’s being affected by the gravitational wave and those pulses arrive a little later,” said Oregon State University astrophysicist Xavier Siemens, a co-director of the NANOGrav. The results released this week in ‘The Astrophysical Journal Letters’ included 15 years of data from NANOGrav, which has been using telescopes across North America to search for the waves.