An international research team, led by the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, has achieved a significant advancement in measuring the Hubble constant (H0), a critical parameter defining the universe’s expansion rate. Their findings, published in the Monthly Notices of the Royal Astronomical Society, demonstrate that employing pixelized strong-lensing modeling on a galaxy cluster scale can substantially enhance the precision of H0 measurements.
The Hubble constant represents the current rate of expansion of the universe. There has been a longstanding discrepancy, known as the “H0 tension,” which reveals a difference exceeding 5σ between measurements derived from the early universe, such as the cosmic microwave background, and those from late-universe observations, like Type Ia supernovae. This inconsistency has prompted researchers to seek independent and precise measurement techniques.
One promising approach involves using strongly lensed supernovae. This method enables researchers to measure cosmic distances through time delays between multiple images of a supernova, providing an independent inference of H0. Unlike traditional methods that depend on the “cosmic distance ladder,” this approach can yield high-precision cosmological constraints. However, the current limitations in precision stem from uncertainties in modeling the mass distribution of the lensing clusters.
To address this challenge, the research team built upon previous efforts from the CURLING project, developing an innovative pixelized strong lens modeling framework. They utilized a system akin to the supernova “Requiem” located within the MACS J0138.0-2155 galaxy cluster. By comparing H0 inferences from traditional point-source modeling and the pixelized method, the results indicated a remarkable improvement. The pixelized modeling reduced uncertainty to ±0.8 km/s/Mpc, enhancing precision by more than tenfold.
The researchers believe that the integration of high-resolution observational data from facilities like the James Webb Space Telescope (JWST) can further refine these measurements. By fully utilizing the surface brightness information from arc-like multiple-image systems created by the lensing effect, systematic modeling errors can be significantly minimized. This establishes strongly lensed supernovae as a potential high-precision tool for cosmological investigations.
Looking ahead, the team simulated future observations under conditions provided by the Rubin Observatory’s Legacy Survey of Space and Time (LSST). They found that time-delay measurements could attain uncertainties around 1.5%. For the Chinese Space Station Telescope—Multi-Channel Imager (CSST-MCI), they anticipate even greater precision. When combined with pixelized modeling, CSST-MCI observations could constrain H0 to within 0.1 km/s/Mpc.
These findings underline that uncertainties in lens modeling are currently the primary limitation in H0 inference. The combination of high-resolution imaging and pixelized strong-lensing modeling paves the way for achieving percent-level precision in H0 measurements in the near future.
Dr. Xie Yushan, the first author of the study, emphasized the innovation in pixelized modeling, stating, “This approach allows us to leverage all the information encoded in the lensed arcs, rather than relying solely on the positions of multiple images. It is a pivotal step towards precision cosmology using cluster-scale strong lensing.”
Prof. Shan Huanyuan, the corresponding author, remarked on the implications of their work, noting, “With advancements from JWST, Euclid, and the upcoming Chinese Space Station Telescope, we are entering a golden era of strong-lensing research. This study highlights the vast potential for achieving high-precision cosmological measurements as more lensed supernova samples become accessible.”
The research represents a noteworthy stride toward resolving one of modern cosmology’s most pressing challenges. As observational technologies continue to evolve, the prospects for refining our understanding of the universe’s expansion become increasingly promising.
