Astronomers Spot Gigantic Rotating Galaxy Filament

Astronomers have found something that shouldn’t exist, or at least isn’t easy to explain: a cosmic filament 140 million light-years away that’s spinning. Not just the galaxies inside it, mind you. The entire structure appears to be rotating, carrying its galaxies along like horses on a carousel.

The discovery, published in the Monthly Notices of the Royal Astronomical Society, involves 14 hydrogen-rich galaxies arranged in a remarkably thin line, about 5.5 million light-years long but only 117,000 light-years wide. Picture a ghostly thread of pearls, stretched taut across the vacuum, each pearl glowing with starlight and the whole strand gently coiled. This thread sits inside a much larger cosmic filament spanning roughly 50 million light-years and containing over 280 galaxies.

Cosmic filaments are the largest structures in the Universe, vast networks of galaxies and dark matter that form what’s called the cosmic web. They funnel gas and momentum into galaxies, feeding them the raw materials they need to grow. But finding one that rotates as a coherent whole? That’s new, and it raises immediate questions about where all that angular momentum came from.

Spinning Teacups on a Spinning Platform

The researchers, including a team from the University of Cambridge, discovered that many of the galaxies appear to be spinning in the same direction as the filament itself. Far more alignment than random chance would predict. What’s more, galaxies on opposite sides of the filament’s central spine are moving in opposite directions, suggesting the entire structure is rotating around its axis.

Using models of filament dynamics, they calculated a rotation velocity of 110 kilometers per second and estimated the dense central region has a radius of about 163,000 light-years. That’s remarkably fast for something so immense, and current theories of structure formation, which lean heavily on dark matter simulations, don’t easily account for it.

“What makes this structure exceptional is not just its size, but the combination of spin alignment and rotational motion. It’s like 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.”

Dr. Lyla Jung from the University of Oxford, one of the study’s co-lead authors, has a point. This dual rotation suggests that the subtle density fluctuations present right after the Big Bang might have transferred more angular momentum through cosmic structures than standard models predict. Which might mean we need to refine how we think dark matter’s gravitational pull dictates the flow of ordinary matter.

Young, Cold, and Full of Hydrogen

The filament appears to be relatively young and undisturbed. It has a large number of gas-rich galaxies and exhibits what astronomers call a dynamically cold state, meaning there’s little random internal motion. Since hydrogen is the raw material for star formation, galaxies containing lots of hydrogen gas are actively gathering or retaining fuel. Studying them offers a window into early stages of galaxy evolution.

Hydrogen-rich galaxies are also excellent tracers of gas flow along cosmic filaments. Because atomic hydrogen is easily disturbed by motion, its presence helps reveal how gas gets funneled through these structures into galaxies, offering clues about how angular momentum flows through the cosmic web to influence galaxy structure, spin, and star formation.

“This filament is a fossil record of cosmic flows. It helps us piece together how galaxies acquire their spin and grow over time.”

Dr. Madalina Tudorache from Cambridge’s Institute of Astronomy, the other co-lead author, is describing what amounts to a cosmic archaeological site. The filament preserves information about processes that shaped galaxies billions of years ago, processes we can still observe today because the structure hasn’t been thoroughly scrambled by subsequent interactions.

The discovery also has practical implications for upcoming cosmology surveys. Future missions like the European Space Agency’s Euclid mission and the Vera C. Rubin Observatory in Chile will study weak gravitational lensing to map dark matter. But intrinsic alignments of galaxies, like the ones in this filament, can contaminate those measurements. Understanding these spinning structures provides a critical benchmark for interpreting future data.

The team made the discovery using South Africa’s MeerKAT radio telescope, an array of 64 interlinked satellite dishes with unparalleled sensitivity to faint hydrogen signals. They combined MeerKAT data from a deep sky survey called MIGHTEE with optical observations from the Dark Energy Spectroscopic Instrument and the Sloan Digital Sky Survey to reveal this cosmic filament exhibiting both coherent galaxy spin alignment and bulk rotation.

Further observations are planned to determine whether this is a common but previously unseen phenomenon or a truly exceptional structure. Either answer would be interesting.

Monthly Notices of the Royal Astronomical Society: 10.1093/mnras/staf2005