Astronomers Took One Step Closer to a New Method for Detecting Gravitational Waves

The secret lies in 'red noise.'
Brad Bergan
A computer generated 3D model of a black hole, and gravitational waves.andreusK / iStock

Modern astronomy is exceeding its own limits, with new discoveries rivaled in impact only by new and emerging ways of advancing the frontiers of the field.

And one of these fields, the study of gravitational waves from unspeakably distant supermassive black holes, is on the verge of a minor revolution. The latest findings from multiple research teams suggest that the collaborative global effort to confirm the viability of a radical new method for detecting the waves is already paying off, according to a recent study published in the journal Monthly Notices of the Royal Astronomical Society.

Specifically, astronomers in North America, Australia, and Europe have probed extension data on the cosmos, and noticed a kind of "red noise" that precisely matches predictions.

In other words, the study of gravitational waves, and thus the early universe, seems primed to receive a major upgrade.

Exploring the early universe via gravitational waves

"This is a major milestone," said Astronomer Michael Kramer of the Max Planck Institute for Radio Astronomy, who helps lead the European team, in a Nature report. While the "red noise" observation doesn't mean the new method has actually detected gravitational waves, it's a crucial step on the path to doing so, added Kramer.

If the red noise hadn't shown up by now, cosmologists may have needed to change their predictions regarding how populous and causally effective supermassive black holes were during the salad days of the early universe. So, while this isn't the final step in forging a new path to explore gravitational waves in the ancient history of the universe, "it's reassuring," said Radio Astronomer Xavier Siemens of Oregon State University, who leads the North American group, in the report.

Detecting gravitational waves in background 'red noise'

This comes roughly seven years after the first direct detection of gravitational waves was made in 2015, when the Laser Interferometry Gravitational-Wave Observatory (LIGO) — based in both Washington state and Louisiana — confirmed something incredible. Using its duo of antennas, LIGO measured waves that were generated in the last moments of two black holes, and both of them had a mass that dwarfed our sun's, 10 times more massive. Since this groundbreaking discovery, LIGO and Virgo (a similar array, in Italy), have witnessed dozens of other gravitational wave events. These are waves whose frequencies can reach frequencies up to thousands of cycles, every second. Notably, this is much like the lower frequencies of audible sound, which is part of why it can be detected for seconds, or, sometimes, minutes.

And, in both 2020 and 2021, the three axes of scientists working on detecting gravitational waves with novel techniques have all seen the key evidence that the waves are lying in wait: specifically, the red noise phenomenon. By contrast, "white" noise consists of the random fluctuations observed at all frequencies in the universe, which simply means we're living in a cosmos. Red noise, on the other hand, is louder than that, and kicks in at lower frequencies. The collaborative analysis has looked at data on 65 different pulsars, to enhance the method's sensitivity to gravitational waves. And, when another paper comes out later this year or in 2023, this same data could be used to finally confirm gravitational waves in the background red noise generated by supermassive black holes.

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