“Exceptional” 5.5-Million-Light-Year-Long Cosmic Structure Appears To Be Rotating, Challenging Current Models Of The Universe

Cosmic filaments, vast, thread-like structures of gas and dark matter, are some of the largest structures known in the universe. 

“Astronomers theorize that the early universe was very smooth, and that the distribution of matter was uniform with tiny variations in density that grew into a web-like pattern,” NASA explains. “These areas of slightly higher density also had slightly more gravity to attract more matter. Over time, the universe evolved into a web of filaments and vast sheets, largely made of dark matter, which form the structure of the universe today.”

Cosmic filaments make up the large-scale “backbone” of the universe, the cosmic web. We have known about the cosmic web since the 1970s and 1980s, so what’s new? Looking at 14 galaxies 140 million light-years away, researchers found that they form a “very thin elongated structure” around 5.5 million light-years long and 117,000 light-years wide, embedded within a far larger filament around 50 million light-years long, and containing over 280 galaxies. 

That’s impressively large compared to other structures in the universe, or, for example, Danny DeVito. But what is weird about this structure is that the galaxies within it appear to be rotating in a common direction, or at least more of them than our current models would predict.

“Understanding the cold atomic hydrogen gas (H I) within cosmic filaments has the potential to pin down the relationship between the low density gas in the cosmic web and how the galaxies that lie within it grow using this material,” the international team led by scientists at the University of Oxford explains in their paper.

“We find that the spin axes of the H I galaxies are significantly more strongly aligned with the cosmic web filament than cosmological simulations predict, with the optically-selected galaxies showing alignment to a lesser degree.”

Many of the galaxies appear to be rotating in the same direction as the filament they find themselves within, rather than being more randomly distributed as you might expect from the universe. Looking at galaxies’ relative velocities with respect to the filament, the team found that those to the west of the filament were receding, while those to the east were approaching. From this they inferred that the whole structure was rotating, perhaps making it the largest rotating structure ever found.

“What makes this structure exceptional is not just its size, but the combination of spin alignment and rotational motion,” co-lead author Dr Lyla Jung from the Department of Physics at the University of Oxford explained in a statement. “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.”

Looking at the galaxies within the rotating structure, they found them to be gas-rich and with low internal motion, indicating that they are likely in the early stages of galaxy development, giving us a glimpse of the early stages of their evolution. Studying this structure, and others like it, could help us understand how galaxies acquire their spin.

“This structure demonstrates that within the cosmic filament, the angular momentum of galaxies is closely connected to the large-scale filamentary structure,” the team adds in their paper. “We also find strong evidence that the galaxies are orbiting around the spine of the filament, making this one of the largest rotating structures discovered thus far, and from which we can infer that there is transfer of angular momentum from the filament to the individual galaxies.”

Previous studies have found similarly puzzling results. Galaxies that are nearer to each other have been found to rotate in the same direction by one team, while looking at 256 galaxies in the early universe found that 40 percent rotated in the counterclockwise direction, while 60 percent rotated in the clockwise direction. Though these are disparate studies, and more research is needed, tracing hydrogen-rich galaxies (as hydrogen is more sensitive to motion) could be a way to get a better idea of how galaxies are given their spin.

“This filament is a fossil record of cosmic flows,” co-lead author Dr Madalina Tudorache from the Institute of Astronomy at the University of Cambridge and the Department of Physics at the University of Oxford, added. “It helps us piece together how galaxies acquire their spin and grow over time.”

The study is published in Monthly Notices of the Royal Astronomical Society.