Powell, D.M.McKean, John P.Vegetti, S.Spingola, C.White, S.D.M.Fassnacht, C.D.2026-04-222026-04-222025-11Powell, D.M., McKean, J.P., Vegetti, S. et al. 2025, 'A million-solar-mass object detected at a cosmological distance using gravitational imaging', Nature Astronomy, vol. 9, pp. 1714-1722. https://doi.org/10.1038/s41550-025-02651-2.2397-3366 (online)10.1038/s41550-025-02651-2http://hdl.handle.net/2263/109675DATA AVAILABILITY : The VLBI dataset is publicly available on the EVN archive https://archive.jive.nl/scripts/portal.php (Experiment GM068). The Keck AO observation used in Fig. 1 is publicly available on the Keck Observatory Archive https://koa.ipac.caltech.edu/ (Program ID U085N2L).Structure on subgalactic scales provides important tests of galaxy formation models and the nature of dark matter. However, such objects are typically too faint to provide robust mass constraints. Here we report the discovery of an extremely low-mass object detected by means of its gravitational perturbation to a thin lensed arc observed with milli-arcsecond-resolution very long baseline interferometry. The object was identified using a non-parametric gravitational imaging technique and confirmed using independent parametric modelling. It contains a mass of m80 = (1.13 ± 0.04) × 106 M⊙ within a projected radius of 80 pc at an assumed redshift of 0.881. This detection is extremely robust and precise, with a statistical significance of 26σ, a 3.3% fractional uncertainty on m80 and an astrometric uncertainty of 194 μas. This is the lowest-mass object known to us, by two orders of magnitude, to be detected at a cosmological distance by its gravitational effect. This work demonstrates the observational feasibility of using gravitational imaging to probe the million-solar-mass regime far beyond our local Universe.en© The Author(s) 2025. This article is licensed under a Creative Commons Attribution 4.0 International License.Million-solar-mass regimeGalaxy formation modelsNature of dark matterGravitational perturbationSpace sustainabilityArticle