Scientists have discovered one of the universe's largest spinning structures, a 50-million-light-year-long cosmic filament. This filament is a thread in the cosmic web, primarily composed of dark matter, and laced with ordinary matter. It's located 140 million light-years away and has a nested structure. At its core, a row of 14 galaxies is almost precisely placed in a line, 5.5 million light-years long and 117,000 light-years wide. These galaxies are rich in hydrogen gas, essential for forming stars. This row of galaxies is embedded in a larger filament, which is 50 million light years in length and is home to about 300 galaxies in total.
The discovery challenges astronomers' understanding of how the environment influences galactic evolution. What makes this structure exceptional is the combination of spin alignment and rotational motion. It's akin to a teacups ride at a theme park, where each galaxy spins like a teacup, but the entire platform, the cosmic filament, also rotates. This dual motion provides a rare glimpse into how galaxies gain their spin from the larger structures they inhabit.
Lyla Jung and Madalina Tudorache, both from the University of Oxford, led the study using the MeerKAT radio telescope in South Africa. They tracked the motion of neutral hydrogen gas in the galaxies and the filament, combining it with optical data from the Dark Energy Spectroscopic Instrument and the Sloan Digital Sky Survey. In 2022, astronomers discovered that filaments in the cosmic web are rotating, based on the motion of the galaxies within them. This new finding that galaxies spin on their axis in the same direction as the filament rotates is surprising, as it contradicts the prevailing theory of how galaxies form.
The gas, stars, and dust in the Milky Way galaxy, for example, rotate around the galactic center. It will take our sun and solar system 220 million years to complete one orbit of the galaxy. The rotation of a galaxy is partly a legacy of the spinning cloud of gas that originally formed it 13 billion years ago, passing its angular momentum to the galaxy. However, since then, most galaxies have experienced close encounters, collisions, and mergers that can disrupt their spin.
The rotation of this filament clearly dominates how the galaxies within it spin, possibly by funneling hydrogen gas along the dark-matter filament and onto the galaxies, coercing their spin while providing further fuel for star formation. This filament is a fossil record of cosmic flows, helping us understand how galaxies acquire their spin and grow over time. The galaxies in the filament also seem relatively young and in an early stage of development, which could alter their spins as they mature.
The discovery of the alignment of galaxies in the spinning filament was reported in the journal Monthly Notices of the Royal Astronomical Society. This finding will lead to important modifications in models of how galaxies form and could influence measurements made as part of weak lensing surveys, such as the Legacy Survey of Space and Time on the Vera C. Rubin Observatory in Chile, which is about to begin work after revealing its first-light images this past summer.
