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For the first time, an international research team led by the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences has demonstrated that applying pixelized strong-lensing modeling on a galaxy cluster scale can significantly improve the precision of the inferred Hubble constant (H₀)鈥攁 key parameter that describes the expansion rate of the universe.

Their findings, published in , provide a new technical pathway for precisely determining the cosmic distance scale through strongly lensed supernovae.

The Hubble constant describes the current expansion rate of the universe and is a core parameter in modern cosmology. However, a discrepancy of over 5蟽, known as the famous "H₀ tension," persists between measurements from the early universe (e.g., cosmic microwave background) and the late universe (e.g., Type Ia supernovae). Finding an independent and highly precise measurement method has thus become crucial to resolving this tension.

Strongly lensed supernovae directly measure cosmic distances through time delays between their multiple images, thereby independently inferring H₀. This method does not rely on the "cosmic distance ladder" and can theoretically provide extremely high-precision cosmological constraints. However, its precision is currently limited by uncertainty in modeling the mass distribution of the lensing clusters.

Building on earlier work from the CURLING project, the researchers developed a pixelized strong lens modeling framework. Using a system similar to the supernova "Requiem" in the MACS J0138.0-2155 galaxy cluster, the researchers compared the H₀ inferences of traditional point-source modeling and the pixelized method.

The results show that the pixelized modeling compressed the uncertainty to 卤0.8 km/s/Mpc, improving the precision by more than tenfold. This indicates that, supported by high-resolution observational data from facilities like the James Webb Space Telescope (JWST), fully utilizing the surface brightness information from arc-like multiple-image systems produced by the lensing effect can significantly reduce modeling systematic errors. This makes strongly lensed supernovae a potential high-precision cosmological probe.

The researchers also simulated future observations of upcoming survey facilities. Under Rubin Observatory's Legacy Survey of Space and Time (LSST) conditions, time-delay measurements could achieve uncertainties of about 1.5%. For the Chinese Survey Space Station Telescope鈥擬ulti-Channel Imager (CSST-MCI), the precision can be further improved. When combined with pixelized modeling, CSST-MCI observations could constrain H₀ to within 0.1 km/s/Mpc.

These results highlight that lens-model uncertainties are now the dominant limitation in H₀ inference. The combination of high-resolution imaging and pixelized strong-lensing modeling paves the way toward achieving percent-level precision in H₀ measurements in the near future.

"Pixelized modeling allows us to use all the information encoded in the lensed arcs, rather than relying only on the positions of multiple images. This is a key step toward precision cosmology with cluster-scale strong lensing," said Dr. Xie Yushan, first author of the study.

"With JWST, Euclid, and the upcoming Chinese Space Station Telescope, we are entering a golden era of strong-lensing research. This work demonstrates the tremendous potential for achieving high-precision cosmological measurements once more lensed supernova samples become available," said Prof. Shan Huanyuan, corresponding author of the study.