New 'Stochastic Siren' Method Uses Gravitational Waves to Measure Universe's Expansion Rate

Researchers develop innovative approach to resolve Hubble tension by analyzing background gravitational waves from black hole mergers.

Published on Feb. 25, 2026

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A research team from the University of Illinois Urbana-Champaign and the University of Chicago has developed a new 'stochastic siren' method that uses the gravitational-wave background from merging binary black holes to provide an independent measurement of the Hubble constant, the expansion rate of the universe. This approach aims to help resolve the ongoing 'Hubble tension' - the mismatch between expansion rate measurements from early-universe and late-universe observations.

Why it matters

Accurately measuring the Hubble constant is crucial for understanding the composition and evolution of the universe. The persistent disagreement between different measurement techniques has led theorists to consider major changes to the standard cosmological model, such as the possibility of early dark energy or interactions between dark matter and neutrinos. Independent methods like the stochastic siren approach can help identify any hidden biases in existing techniques and provide a more definitive answer.

The details

The new method analyzes the collective 'hum' of unresolved gravitational-wave events from binary black hole mergers across the universe. The strength of this background depends on the expansion history of the universe, as captured by the Hubble constant. By combining this background information with data on individually detected binary black hole mergers, the researchers were able to shift and tighten their inferred Hubble constant measurement compared to using the resolved merger data alone.

  • The research team analyzed data from the first three observing runs of the LIGO-Virgo-KAGRA gravitational-wave detector network.
  • The paper describing the new method has been accepted for publication in Physical Review Letters.

The players

Nicolás Yunes

Professor of Physics at the University of Illinois Urbana-Champaign and one of the authors of the study.

Bryce Cousins

Physics graduate student at the University of Illinois Urbana-Champaign and lead author of the study.

Daniel Holz

Professor of Physics and Astronomy & Astrophysics at the University of Chicago and a co-author of the study.

LIGO-Virgo-KAGRA Collaboration

The global network of gravitational-wave detectors that provided the data analyzed in the study.

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What they’re saying

“It's important to obtain an independent measurement of the Hubble constant to resolve the current Hubble tension. Our method is an innovative way to enhance the accuracy of Hubble constant inferences using gravitational waves.”

— Nicolás Yunes, Professor of Physics (Physical Review Letters)

“It's not every day that you come up with an entirely new tool for cosmology. We show that by using the background gravitational-wave hum from merging black holes in distant galaxies, we can learn about the age and composition of the universe.”

— Daniel Holz, Professor of Physics and Astronomy & Astrophysics (Physical Review Letters)

What’s next

The researchers note that future upgrades to the LIGO-Virgo-KAGRA detectors are expected to allow the direct observation of the gravitational-wave background within the next year, which could further strengthen the stochastic siren method and its ability to resolve the Hubble tension.

The takeaway

This new stochastic siren approach represents an innovative way to leverage the collective signal of unresolved gravitational-wave events to independently measure the expansion rate of the universe, providing a valuable tool to help settle the longstanding Hubble tension and improve our understanding of cosmology.