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A community-built distance network sharpens the Hubble constant and broadens the evidence behind the \u201cHubble tension\u201d.<\/strong><\/em><\/p>\n BERN, SWITZERLAND \u2013 An international collaboration of astronomers has achieved the most precise direct<\/strong> measurement to date of the current expansion rate of the Universe. In a paper to be published in Astronomy & Astrophysics<\/em>, the H0 <\/sub>Distance Network<\/em> (H0DN<\/em>) Collaboration reports a value of the Hubble constant of H\u2080<\/em> = 73.50 \u00b1 0.81 km s\u207b\u00b9 Mpc\u207b\u00b9<\/strong>, corresponding to a precision of just over 1%.<\/p>\n For nearly a century, astronomers have relied on the so-called \u201cdistance ladder\u201d to measure the expansion rate of the Universe\u2014the Hubble constant, H\u2080<\/em>\u2014by calibrating increasingly distant cosmic objects through a sequence of interlocking steps. This method has delivered tremendous progress, but it also means that uncertainties can propagate along the chain, without the benefit of spreading risk or sharing the load. The H0<\/sub>DN Collaboration therefore adopted a broader mathematical framework, replacing a single measurement path with a Local Distance Network that links many distance indicators simultaneously.<\/p>\n Rather than depending on any single measurement path, the network connects a wide range of independent and overlapping distance indicators<\/strong> \u2013 including Cepheid variables, the Tip of the Red Giant Branch (TRGB), Mira variables, megamasers, Type Ia and Type II supernovae, surface brightness fluctuations, the Tully-Fisher relation, and the Fundamental Plane \u2013 into a single, coherent analysis.<\/p>\n Crucially, the network explicitly accounts for shared uncertainties and correlations between methods through full covariance weighting, allowing the consistency of the entire system to be assessed transparently for the first time.<\/p>\n \u201cThis isn\u2019t just a new number for H\u2080,\u201d <\/em>the collaboration notes, \u201cit\u2019s a community-built framework that brings decades of independent distance measurements together, transparently and accessibly.\u201d<\/em><\/p>\n Nearly 40 experts<\/strong> in distance measurements and cosmology, representing a wide range of institutions and methodological backgrounds, participated directly in the ISSI workshop, with additional contributors joining remotely. Before any calculations were carried out, participants voted on the set of first-rank distance indicators, gold standards for defining a baseline solution, along with predefined variants to test robustness.<\/p>\n The network analysis shows that:<\/p>\n To encourage scrutiny and reuse, the collaboration is releasing open-source software and data products<\/strong>, allowing anyone to reproduce the analysis, explore alternative assumptions, or incorporate future measurements as new data become available.<\/p>\n With its unprecedented precision and internal consistency, the new local measurement remains in significant disagreement with values inferred from observations of the early Universe under the assumption of the standard \u039bCDM cosmological model. The reported H\u2080<\/em> differs by approximately 5\u20137 standard deviations<\/strong> from recent determinations based on the cosmic microwave background and baryon acoustic oscillations.<\/p>\n Rather than pointing to a specific flaw in any single measurement technique, the distance-network result broadens the basis of the local measurement of the Hubble constant.<\/p>\n \u201cThis work effectively rules out explanations of the Hubble tension that rely on a single overlooked error in local distance measurements,\u201d <\/em>the authors conclude. \u201cIf the tension is real\u2014as the growing body of evidence suggests\u2014it may point to new physics beyond the standard cosmological model.\u201d<\/em><\/p>\n Beyond delivering the most precise direct measurement of the Hubble constant to date, the Local Distance Network establishes a flexible and extensible framework for the future. With a flood of new observatories, improved calibrations, and additional geometric distance anchors becoming available, they can be integrated into the network to further refine our understanding of cosmic expansion and provide clues about the resolution of the Hubble tension.<\/p>\n \u201cThis work shows that explanations invoking a single overlooked systematic in local distance measurements are increasingly difficult to sustain,\u201d<\/em> the authors conclude. \u201cIf the tension reflects real physics, it may indicate new ingredients beyond the standard cosmological model or require a reassessment of early-Universe inferences.\u201d<\/em><\/p>\n The study also highlights the role of ISSI Bern in fostering open, collaborative, and methodologically rigorous science that bridges traditional disciplinary and institutional boundaries<\/strong>.<\/p>\n The full paper will appear in Astronomy & Astrophysics. Upon acceptance, the analysis code will be made publicly available via GitHub and the Astrophysics Source Code Library.<\/em><\/p>\n Press release text by Fabio Crameri (ISSI) in collaboration with the authors.<\/p>\nA network, not a single path<\/strong><\/h3>\n
Robust, transparent, and community-driven<\/strong><\/h3>\n
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Implications for the Hubble tension<\/strong><\/h3>\n
A foundation for future precision cosmology<\/strong><\/h3>\n
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