Astrophysicists at the University of Illinois and the University of Chicago have developed an innovative method to measure the Hubble constant (the rate of expansion of the universe) using the subtle background sound of gravitational waves. As the sensitivity of gravitational wave detectors increases in the coming years, this approach could reshape our understanding of the history of the universe and help resolve central debates in modern astrophysics.
A schematic diagram of the expansion of the universe from the Big Bang to the present. Image credit: NASA/EFBrazil.
“This result is very important. Obtaining independent measurements of the Hubble constant is critical to solving the current problem.” hubble tension” said Nicholas Younes, a professor at the University of Illinois.
“Our method is an innovative way to use gravitational waves to improve the accuracy of Hubble constant inference.”
Professor Younes and his colleagues have proposed a gravitational wave-based technique that uses faint “background hum” from countless distant black hole collisions to refine estimates of the Hubble constant.
Unlike traditional methods, this new approach takes advantage of ripples in space-time itself, or gravitational waves. Gravitational waves convey information about vast distances and the speed at which objects are moving apart.
Astrophysicists call this the “stochastic siren” method.
“Because we are observing individual black hole collisions, we can determine the rate of those collisions occurring throughout the universe,” said Bryce Cousins, a graduate student at the University of Illinois.
“Based on their speed, we expect there to be many more events that we cannot observe, called the gravitational wave background.”
“It’s not every day that you come up with a completely new tool for cosmology,” added University of Chicago professor Daniel Holtz.
“We have shown that we can learn about the age and composition of the universe by harnessing the background sound of gravitational waves resulting from the merger of black holes in distant galaxies.”
“This is an exciting and entirely new direction, and we look forward to applying our method to future datasets to help constrain the Hubble constant and other important cosmological quantities.”
As gravitational wave detectors become more sensitive in the coming years, the stochastic siren method could become the basis for precision cosmology.
Gravitational wave backgrounds are expected to be detected within the next six years.
Up to that point, the method progressively limits higher values of the Hubble constant as the upper background limit improves, providing another probe of the Hubble tension without full detection.
“This should pave the way for future applications of this method, as we continue to increase sensitivity and be able to better suppress and perhaps even detect the gravitational wave background,” Cousins said.
“We hope that including that information will yield better cosmological results and move us closer to resolving the Hubble tension.”
team’s work will be published in journal physical review letter.
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Bryce Cousins others. 2026. Stochastic sirens: Astrophysical gravitational wave background measurements of the Hubble constant. Physics. pastor rhettin press. doi: 10.1103/4lzh-bm7y