New Measurement Methods Advance Hubble Constant Research

Several scientific teams are developing independent methods to measure the Hubble constant, a key parameter describing the universe’s expansion rate. These approaches use gravitational lensing and gravitational-wave observations to provide alternatives to traditional techniques.

One method, known as time-delay cosmography, relies on the effect of strong gravitational lensing of quasars. By analyzing the time delays in light paths caused by massive objects bending light, researchers can determine the Hubble constant without depending on earlier measurement systems.

This lensing-based technique currently achieves a precision of about 4.5% when using data from eight different lens systems. Research groups plan to expand the number of studied systems and improve mass-distribution models, aiming to reach a precision between 1% and 2% in future measurements.

Other teams are utilizing gravitational-wave data to estimate the Hubble constant. The stochastic siren approach analyzes the gravitational-wave background generated by binary black-hole mergers, while another method cross-correlates so-called “dark siren” gravitational-wave events with galaxy distributions to infer the expansion rate.

What the numbers show

• Time-delay cosmography achieves ~4.5% precision using eight lens systems
• Forecasts indicate ~20% accuracy at O4 and ~2.7% at O5 gravitational-wave detector sensitivity
• Model-independent analysis finds Hubble constant tension less than 2σ compared to SH0ES result

Researchers at the University of Illinois Urbana-Champaign and the University of Chicago have developed a new method that uses the gravitational-wave background, described as a “hum” from merging black holes, to refine Hubble constant measurements. This approach is designed to improve upon earlier gravitational-wave techniques.

The Illinois-Chicago method is expected to provide tighter constraints on the Hubble constant as upper limits on the gravitational-wave background improve, even before a full detection is achieved. This could allow for more accurate upper limits on the expansion rate in the near term.

Another model-independent technique combines gravitational-wave standard siren data with electromagnetic observations using Gaussian processes. This analysis has found results for the Hubble constant that are consistent with the SH0ES measurement, with a reported tension of less than two standard deviations.

Forecasts using current gravitational-wave detector networks and population-based methods suggest that a 20% accuracy in the Hubble constant may be reached at O4 sensitivity, improving to approximately 2.7% at O5 sensitivity. These developments show ongoing progress in refining the universe’s expansion rate through multiple independent scientific approaches.

* This article is based on publicly available information at the time of writing.