We present a purely observational detection of coherent Eulerian circulation on filamentary scales in the reconstructed cosmic velocity field. Using the Cosmicflows-4 peculiar-velocity reconstruction, we analyze the velocity field around geometrically identified cosmic filaments from an explicitly Eulerian perspective. Rather than relying on galaxy or halo angular momentum, we directly measure tangential velocity structure in planes transverse to filament spines, enabling a field-based characterization of rotational motion. Applied to a local filament sample, this analysis reveals a selective subset of filaments exhibiting coherent, radius-dependent tangential motion extending over several megaparsecs. Many filaments remain consistent with null circulation, indicating that filament-scale rotation is not a universal property of the cosmic web. Two independent null tests establish the robustness of the signal. Randomization of filament axes strongly suppresses the detected circulation, demonstrating geometric alignment with filament orientations. Relocation of filament segments to distant environments likewise eliminates the signal, indicating sensitivity to the surrounding large-scale velocity field rather than filament geometry alone. These results establish filament-scale Eulerian circulation as an observational property of the reconstructed cosmic velocity field. The analysis and accompanying data products provide a reproducible foundation for future studies of large-scale cosmic flows and filament dynamics.
Daniel Beaupré (2026) studied this question.