Intergalactic filaments spin.

Matter in the Universe is distributed in a cosmic web, with a filament of matter typically connecting neighboring galaxy pairs, separated by tens of millions of light-years. Filaments are known to influence the spins of galaxies around them, but it remains unknown whether filaments themselves spin. Here, we measure the angular momentum around intergalactic filaments in a dark-matter cosmological simulation, finding that matter generally rotates substantially around them. Our results suggest that spin is a fundamental property of filaments, part of a full picture of structure formation. Filaments are likely to be the longest coherently rotating objects in the Universe. This finding helps to explain how galaxies spin in the cosmic web, and could provide a mechanism to generate intergalactic magnetic fields.