Astrophysicists record ‘murmur’ of the universe – 06/29/2023 – Science

An American-Canadian team of astrophysicists has recorded the sound of gravitational waves — alterations in the fabric of the cosmos caused by the movement and collision of gigantic objects in space. The discovery, published this Thursday (29) in The Astrophysical Journal Letters, confirms a hypothesis proposed by the German scientist Albert Einstein more than a century ago.

Gravitational waves create a very low-frequency background noise that permeates the cosmos, comparable to the murmur of a large crowd. Space would be full of these waves that oscillate over extended periods, spanning light years. Their primary origin is pairs of gigantic black holes, spiraling and merging.

The data for this report was collected over 15 years by the North American Nanohertz Observatory for Gravitational Waves (NanoGrav) Physics Frontiers Center, which brings together more than 190 scientists from the United States and Canada.

“It’s really the first time we have evidence of this large-scale motion of everything in the universe,” commented Maura McLaughlin, co-director of NanoGrav.

Einstein already intuited

Albert Einstein (1879-1955) first proposed in 1916 the existence of gravitational waves in spacetime, as an extension of his revolutionary Theory of General Relativity. According to this, gravity would be a distortion of space and time caused by matter.

However, having relied on indirect evidence since the 1970s, it wasn’t until 2016 that science directly detected these ripples — comparable to the concentric circles formed by an object falling into water. NanoGrav’s research has focused heavily on pulsars—ultradense remnants of stars that have exploded, swirling at extraordinary speeds.

“Gravitational waves are generated by astronomically dense objects, typically in reciprocal orbital motion. As they travel through space, these waves physically stretch and contract the fabric of spacetime itself,” Jeff Hazboun, an astrophysicist at State University, told Reuters. from Oregon, USA, and main author of one of the works published in the journal.

Scientists have compared cosmic background noise, generated by black holes or other mega-objects, to the low-pitched hum of a large human gathering, where individual voices are indistinguishable.

Seven years ago, gravitational waves generated by two black holes – regions of space-time with such intense gravity that not even light can escape – were detected for the first time. For this study, the Laser Interferometer Gravitational-Wave Observatory (Ligo) was used.

According to Hazboun, “we now have overwhelming evidence of the murmur of gravitational waves on another frequency scale, much smaller. They are ten to 12 orders of magnitude below those detected by LIGO, with wavelengths that last light years”.

“The most direct explanation for these gravitational waves would be a series of pairs of black holes orbiting each other in our cosmic neighborhood. However, alternative explanations perhaps involve a curious new physics, related to the early stages of the universe, close to the Big Bang, about 13.8 billion years ago.”