For first time, scientists ‘hear’ sound of gravitational waves

For first time, scientists ‘hear’ sound of gravitational waves

Until their detection in 2016, scientists had found only indirect evidence of their existence, beginning in the 1970s.

In what has been described as a groundbreaking discovery, scientists have for the first time “heard” the sound of gravitational waves produced by the slow-motion mergers of supermassive black holes.

The international research consortium, including astrophysicists from India, on Wednesday, recorded the gravitational waves rippling through the fabric of space-time. It is said that they are by far the most powerful ever measured.

The discovery was made by scientists from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), who have been closely observing stars called pulsars that act as celestial metronomes.

For first time, scientists ‘hear’ sound of gravitational waves
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Albert Einstein first predicted the existence of gravitational waves a century ago, but it was proved only in 2016 when the US-based Laser Interferometer Gravitational-Wave Observatory (Ligo) detected the merger of blackholes, effectively proving that space itself can be stretched and squeezed.

Until their detection in 2016, scientists had found only indirect evidence of their existence, beginning in the 1970s.

Also, the one discovered in 2023 is markedly different from the 2016 gravitational waves as the scientists at that time were able to capture only short “chirps” of gravitational waves linked to mergers of black holes or neutron stars only slightly larger than the sun.

"We’ve opened a new window of observation on the universe,” said Chiara Mingarelli, an astrophysicist and assistant professor at Yale University in the US, and a member of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) team.

Sound of 'choir'

Mingarelli likened the new class of gravitational waves to a “choir, with the pairs of supermassive black holes chiming in at different frequencies”. She also said the gravitational wave background was “about twice as loud as I’d expected”.

Objects called pulsars —extremely dense cores of exploded stars that spin at the speed of kitchen blenders —were crucial in the new research. Nearly 70 pulsars were used in gathering the evidence.

“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.

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