Chinese team finds key evidence for low-frequency gravitational waves with FAST telescope

Similar findings were also released by teams from the United States, Canada, Europe, India and Australia independently at about the same time.

Maura McLaughlin from West Virginia University, who is co-director of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), said the CPTA result was exciting and the team should be congratulated.

“They are fortunate to have access to the world’s largest radio telescope, which has allowed them to measure a very significant signal in a short time span,” McLaughlin said.

NANOGrav’s findings, based on four major radio telescopes in the US and Canada and more than 15 years of observation, were published on Thursday in a different peer-reviewed journal, The Astrophysical Journal Letters, with a confidence level of about 4 sigma.

None of the findings released on Thursday met the gold standard in physics to claim the detection of the waves, which would require 5 sigma or 99.99994 per cent confidence level, or an error probability of less than one in a million.

When massive objects accelerate, they slightly squeeze or stretch surrounding space-time to create gravitational waves. Therefore, gravitational waves carry information about the sources that produce them and are particularly useful for studying sources that do not emit light.

Just like light waves, gravitational waves are emitted over many orders of magnitude in frequency, and different types of detectors are needed to observe the entire gravitational wave spectrum.

For decades, scientists have used radio telescopes and a technique known as pulsar timing array to look for a type of gravitational wave that has nanohertz frequencies, and are the only means to study the formation and evolution of large-scale structures in the early universe.

From 2019, China’s FAST telescope joined the hunt by monitoring 57 ultra-precise millisecond pulsars – extremely dense, fast-spinning balls of neutrons which emit lighthouse-like beams to sweep past Earth hundreds of times per second – and using them as a galaxy-sized detector to search for space-time disturbances caused by nanohertz gravitational waves.

Researchers from the National Astronomical Observatories and Peking University developed their own software and algorithms, and spotted a so-called quadrupole correlation signal in the pulsar data set, which was theoretically predicted to be uniquely linked to the waves they were looking for.

“In the race to detect nanohertz gravitational waves, we took full advantage of FAST’s unparalleled sensitivity, high measurement accuracy and its ability to monitor a large number of pulsars,” the team said in a press release.

“Now, China has a front-row seat in nanohertz gravitational wave research and we are finally opening a brand new window on the gravitational-wave universe.”