Astronomers unveil evidence of "background hum" in universe

Astronomers have unveiled evidence of a phenomenon known as the “background hum” in the universe, marking a significant breakthrough. Researchers from various countries, including North America, Europe, China, India, and Australia, collaborated on this achievement, utilizing radio telescopes over several years.

This discovery provides a new perspective into the cosmos, confirming a theory proposed by Albert Einstein over a century ago.

Gravitational waves, which are disturbances in the fabric of spacetime, travel unimpeded at the speed of light.

Although their existence was confirmed in 2015 when gravitational waves resulting from the collision of two black holes were detected, scientists have long sought to identify low-frequency gravitational waves, akin to a constant background noise permeating space.

Under the International Pulsar Timing Array consortium, scientists employed gravitational wave detectors around the world to reveal compelling evidence of these background waves.

Michael Keith, part of the European Pulsar Timing Array, stated, “We now know that the universe is awash with gravitational waves.” To detect low-frequency waves, astronomers studied pulsars, remnants of stars that exploded as supernovae.

Pulsars emit regular radio wave pulses, akin to cosmic lighthouses, allowing them to serve as extremely precise clocks.

By observing a total of 115 pulsars within the Milky Way, researchers measured minute variations in pulse timing, searching for indicators of gravitational waves.

The team, including French astrophysicist Antoine Petiteau, succeeded in detecting changes as small as one millionth of a second over a span of more than two decades.

The revelation of the waves in 2020 left Maura McLaughlin from the US Pulsar Search Collaboratory program “awestruck.”

While the early evidence aligns with Einstein’s theory of relativity and our current understanding of the universe, the scientists emphasized that the waves have not been definitively “detected” since they have not yet reached the gold-standard level of certainty known as five sigma.

This level indicates a one-in-a-million chance of the findings being a statistical anomaly.

Various countries and groups within the consortium independently published their research in several journals.

Steve Taylor, chair of North America’s NANOGrav gravitational wave observatory, expressed confidence that combining all the data could achieve the five sigma threshold within the next year or two.

The leading theory suggests that these waves originate from pairs of supermassive black holes at the cores of merging galaxies. Unlike the previously detected gravitational waves, these black holes are immensely large, often billions of times the mass of the Sun.

If confirmed, the waves would represent the cumulative effect of countless supermassive black hole binary systems present throughout the universe’s galaxies.

Daniel Reardon, a member of Australia’s Parkes Pulsar Timing Array, described these waves as the “background hum of all these black holes,” analogous to the chatter in a noisy restaurant. Another theory proposes that the gravitational waves originate from the rapid expansion that occurred within a second after the Big Bang, a period called cosmic inflation.

This expansion remains hidden from scientists’ direct observation, as the galaxies between Earth and the Big Bang likely “drown out” these waves. However, low-frequency gravitational waves hold the potential to provide insights into the early expansion and possibly illuminate the mystery of dark matter.

They could also enhance our understanding of black hole and galaxy formation and evolution.