The Local Distance Network: A community consensus report on the measurement of the Hubble constant at ∼1% precision
Stefano Casertano, Gagandeep Anand, Richard I. Anderson, Rachael Beaton, Anupam Bhardwaj, John P. Blakeslee, Paula Boubel, Louise Breuval, Dillon Brout, Michele Cantiello, Mauricio Cruz Reyes, G. Csörnyei, Thomas de Jaeger, Suhail Dhawan, Eleonora Di Valentino, Lluís Galbany, Hector Gil-Marín, D. Graczyk, Caroline D. Huang, Joseph B. Jensen, Pierre Kervella, Bruno Leibundgut, Bastian Lengen, Siyang Li, Lucas Macri, Emre Özülker, Dominic W. Pesce, Adam Riess, M. Romaniello, Khaled Said, Nils Schöneberg, Dan Scolnic, T. Sicignano, D. M. Skowron, Syed A. Uddin, Licia Verde, A. Nota
Abstract
Context. The direct empirical determination of the local value of the Hubble constant ( H 0 ) has markedly advanced thanks to improved instrumentation, measurement techniques, and distance estimators. However, combining determinations from different estimators is nontrivial due to their correlated calibrations and different analysis methodologies. Aims. Using covariance weighting and leveraging community expertise, we have constructed a rigorous and transparent “Distance Network” to find a consensus value and uncertainty for the locally measured Hubble constant. Methods. Experts across all relevant distance measurement domains were invited to critically review the available datasets spanning parallaxes, detached eclipsing binaries, masers, Cepheids, the tip of the red giant branch, Miras, carbon-rich asymptotic giant branch stars, Type Ia (SNe Ia) and Type II supernovae, surface brightness fluctuations, the fundamental plane, and Tully–Fisher relations. Before any calculations, the group voted for first-rank indicators to define a “baseline” Distance Network. Other indicators were included to assess the robustness and sensitivity of the results. We provide open-source software and data products to support full transparency and future extensions of this effort. Results. Our key findings are as follows: (1) The local H 0 is robustly determined, with first-rank indicators internally consistent within their uncertainties. (2) A covariance-weighted combination yields a relative uncertainty of 1.1% (baseline) or 0.9% (all estimators). (3) The contribution from SNe Ia is consistent across compilations of optical or NIR magnitudes. (4) Removing either Cepheids or the tip of the red giant branch has a minimal effect on the central value of H 0 . (5) Replacing SNe Ia with galaxy-based indicators changes H 0 by less than 0.1 km s −1 Mpc −1 while doubling its uncertainty. (6) The baseline result is H 0 = 73.50 ± 0.81 km s −1 Mpc −1 , 7.1 σ from the early Universe plus ΛCDM result 67.24 ± 0.35 km s −1 Mpc −1 and 5.0 σ from BBN+BAO within a flat ΛCDM DESI DR2 (68.51 ± 0.58 km s −1 Mpc −1 ). Conclusions. A networked approach, such as the one presented here, is invaluable for enabling further progress in Hubble constant measurements, as it provides the much needed advances in accuracy and precision without overreliance on any single method, sample, or group.