Astrophysicists from the University of Illinois and the University of Chicago have pioneered a groundbreaking method to determine the Hubble constant, which quantifies the rate of the universe’s expansion. By utilizing the subtle background sound of gravitational waves, this innovative technique is poised to transform our understanding of cosmic evolution and may resolve key debates in contemporary astrophysics.

Schematic diagram of the universe’s expansion from the Big Bang to the present. Image credit: NASA/EFBrazil.

“This discovery holds significant importance. To address the ongoing Hubble tension, obtaining an independent measurement of the Hubble constant is crucial,” stated Professor Nicolas Younes from the University of Illinois.

“Our approach innovatively leverages gravitational waves to enhance the accuracy of Hubble constant measurements.”

Professor Younes and colleagues introduced a novel gravitational wave method utilizing the faint “background hum” from numerous distant black hole mergers to enhance Hubble constant estimations.

In contrast to traditional measurement techniques, this method capitalizes on space-time distortions, or gravitational waves, which carry valuable insights about vast cosmic distances and the velocity of receding celestial bodies.

Astrophysicists have termed this approach the “stochastic siren” method.

“By observing distinct black hole mergers, we can ascertain the frequency of these events throughout the universe,” remarked Bryce Cousins, a graduate student at the University of Illinois.

“Considering their velocity, we anticipate many additional events occurring that remain undetected, referred to as the gravitational wave background.”

“Discovering a completely new tool for cosmological research is a rare occurrence,” added Daniel Holtz, a professor at the University of Chicago.

“We demonstrated that we can unravel the age and composition of the universe by harnessing the ambient sound of gravitational waves resulting from the merger of black holes across distant galaxies.”

“This is an exhilarating and entirely novel direction, and we eagerly anticipate applying our method to future datasets to assist in determining the Hubble constant and other vital cosmological parameters.”

As the sensitivity of gravitational wave detectors improves, the stochastic siren method could lay the foundation for precision cosmology.

Detection of gravitational wave backgrounds is anticipated within the next six years.

Until then, the method gradually restricts higher Hubble constant values as improved upper background limits emerge, providing additional insights into the Hubble tension even without full detection capabilities.

“This initiative should pave the way for future applications, enhancing our sensitivity and ability to better filter and potentially detect the gravitational wave background,” Cousins noted.

“We hope that incorporating this information will yield superior cosmological insights and bring us closer to resolving the Hubble tension.”

The team’s research will be published in the Physical Review Letters.

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Bryce Cousins et al. 2026. Stochastic Siren: Astrophysical Gravitational Wave Background Measurement of the Hubble Constant. Physics. in press. doi: 10.1103/4lzh-bm7y