Cosmic filaments form the main framework of the cosmic web, consisting of long, thread-like arrangements of galaxies and dark matter that channel material across intergalactic space. These structures act as routes along which gas and angular momentum flow into galaxies, so nearby rotating filaments where many galaxies share a common spin direction provide a key testbed for understanding how galaxies acquire their rotation over tens of millions of light-years.

In this study, the researchers identified 14 nearby galaxies rich in atomic hydrogen arranged in a narrow configuration about 5.5 million light-years long and roughly 117,000 light-years across. This string sits within a much larger filament containing more than 280 galaxies and extending about 50 million light-years, where a significant fraction of the galaxies appear to rotate in the same sense as the filament itself, a level of alignment that exceeds expectations from random orientations and challenges current models of how strongly large-scale structures couple to galaxy spins.

Velocity measurements show that galaxies on opposite sides of the filament's central spine move in opposite directions along the line of sight, indicating that the system as a whole is rotating. By modelling the filament dynamics, the team inferred a rotation speed of about 110 kilometers per second and estimated a dense central region with a radius near 50 kiloparsecs, equivalent to roughly 163,000 light-years.

Co-lead author Dr Lyla Jung of the University of Oxford said: "What makes this structure exceptional is not just its size, but the combination of spin alignment and rotational motion. You can liken it to the teacups ride at a theme park. Each galaxy is like a spinning teacup, but the whole platform- the cosmic filament -is rotating too. This dual motion gives us rare insight into how galaxies gain their spin from the larger structures they live in."

The filament appears to be relatively young and undisturbed, with many gas-rich galaxies and low internal motions that indicate a dynamically cold state. Because hydrogen gas provides the basic fuel for star formation, these hydrogen-rich galaxies are still gathering or retaining material for new stars, giving a view of galaxy evolution at an early or ongoing stage.

Atomic hydrogen also serves as a sensitive tracer of motion, making hydrogen-rich galaxies effective markers of gas flows along filaments. Tracking how hydrogen is channelled through the filament into galaxies helps reveal how angular momentum is transported through the cosmic web and how this process shapes galaxy morphology, rotation, and star formation histories.

The discovery has implications for cosmological surveys that use weak gravitational lensing, where intrinsic alignments of galaxy shapes and spins can mimic or contaminate lensing signals. Detailed studies of structures like this filament will improve models of intrinsic alignments for missions such as the European Space Agency's Euclid observatory and the Vera C. Rubin Observatory in Chile, refining measurements of cosmic structure growth and dark matter distribution.

Co-lead author Dr Madalina Tudorache of the University of Cambridge and University of Oxford said: "This filament is a fossil record of cosmic flows. It helps us piece together how galaxies acquire their spin and grow over time."

The team combined radio observations from South Africa's MeerKAT array of 64 linked dishes with optical spectroscopy from the Dark Energy Spectroscopic Instrument and the Sloan Digital Sky Survey. Within the MIGHTEE deep survey, led by Professor of Astrophysics Matt Jarvis at the University of Oxford, these data revealed a filament that shows both coherent alignment of galaxy spins and bulk rotational motion, demonstrating the value of multi-observatory datasets for studying how large structures and galaxies form.

Professor Matt Jarvis said: "This really demonstrates the power of combining data from different observatories to obtain greater insights into how large structures and galaxies form in the Universe. Such studies can only be achieved by large groups with diverse skillsets, and in this case, it was really made possible by winning an ERC Advanced Grant/UKIR Frontiers Research Grant, which funded the co-lead authors."

The collaboration also included researchers from the University of Cambridge, the University of the Western Cape, Rhodes University, the South African Radio Astronomy Observatory, the University of Hertfordshire, the University of Bristol, the University of Edinburgh, and the University of Cape Town.

Research Report:A 15 Mpc rotating galaxy filament at redshift z = 0.032

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