Intergalactic filaments spin
  Matter in the Universe is arranged in a cosmic web, with a filament of matter
typically connecting each neighbouring galaxy pair, separated by tens of
millions of light-years. A quadrupolar pattern of the spin field around
filaments is known to influence the spins of galaxies and haloes near them, but
it remains unknown whether filaments themselves spin. Here, we measure
dark-matter velocities around filaments in cosmological simulations, finding
that matter generally rotates around them, much faster than around a randomly
located axis. It also exhibits some coherence along the filament. The net
rotational component is comparable to, and often dominant over, the known
quadrupolar flow. The evidence of net rotations revises previous emphasis on a
quadrupolar spin field around filaments. The full picture of rotation in the
cosmic web is more complicated and multiscale than a network of spinning
filamentary rods, but we argue that filament rotation is substantial enough to
be an essential part of the picture. It is likely that the longest coherently
rotating objects in the Universe are filaments. Also, we speculate that this
rotation could provide a mechanism to generate or amplify intergalactic
magnetic fields in filaments.
