A string of galaxies rotating individually and in unison with their filament will help us better understand how the primordial ones developed.
One of the largest rotating structures in the Universe has been discovered somewhere in the cosmic web that holds the Universe’s visible matter together.
140 million light years from us, a group of astronomers from the University of Oxford has discovered a long string of galaxies arranged along a thin line, which rotate individually, and at the same time in unison, with the cosmic filament in which they are immersed. This is the largest celestial carousel ever identified, which could reveal how galaxies acquired the rotation and gas they have today.
The results of the study were published in the journal Monthly Notices of the Royal Astronomical Society.
The scaffolding of the Universe
Cosmic filaments are gigantic filamentary structures of gas, dark matter and galaxies that represent the fabric of the cosmic spider web, the scaffolding on which all the structures visible in the Universe are created. We can imagine them as highways along which matter and momentum flow towards the galaxies, which in turn convey towards the “nodes” of the spider web, where the galactic clusters reside.
Nearby filaments, where the entire structure appears to rotate along with the galaxies it contains, are interesting to study because they offer a model of how cosmic rotation (or more properly, angular momentum) builds up over time. The British team studied one by crossing data from the South African MeerKAT radio telescope with optical observations from the Dark Energy Spectroscopic Instrument (DESI) and the Sloan Digital Sky Survey.
A record-breaking ride
The rotating megastructure observed by Oxford scientists is an array of 14 nearby galaxies approximately 5.5 million light-years long and 117,000 light-years wide. This string of galaxies in turn lies within a cosmic filament of more than 280 other galaxies, about 50 million light-years long. But the “astronomical” dimensions are not the only aspect of interest.
Many of the observed galaxies appear to rotate in the same direction as the filament itself, and those on either side of the filament’s intermediate “spine” appear to rotate in opposite directions, as if the entire filament was itself rotating.
As Oxford physicist Lyla Jung, co-author of the study, explained, the structure «can be compared to the teacup carousel in an amusement park. Each galaxy is like a spinning teacup, but the entire platform, the cosmic filament, also rotates. This double motion gives us a rare insight into how galaxies get their spin from the larger structures in which they live.”
A young thread to take as a model
The abundance of hydrogen in galaxies (a gas that fuels the formation of new stars) and the low internal motion of the system suggest that the filament is in an early stage of its development. It could therefore provide a window of study to understand how gases are channeled towards galaxies and how angular momentum flows within the cosmic web, influencing its shape and the formation of new stars.
«This filament is a fossil record of cosmic flows. It helps us reconstruct how galaxies acquire their rotation and grow over time” comments the other co-author, Madalina Tudorache.