An international team of researchers, led by Maryam Arabsalmani of the ORIGINS cluster at Munich’s Ludwig-Maximilians University (LMU), has discovered for the first time a set of cold gas clouds along a cosmic filament. This filament forms a spectacular “string of pearls” in the cosmic web, and consists of eight galaxies aligned in a narrow, rectilinear pattern.
Cosmic filaments are gigantic structures of dark matter, gas and galaxies, linking galactic clusters like cosmic highways. According to theoretical models, they channel cold gas to fuel star formation in galaxies. The study published in The Astrophysical Journal Letters by the research team reveals cold, massive gas clouds, comparable in mass to those of large galaxies, but with no trace of star formation.
A fortuitous discovery
The cosmic filament lies at a redshift of z = 0.037, and was discovered by chance while analyzing the unusual properties of a spiral galaxy with a butterfly-shaped gas distribution. Observations made with the Very Large Array (VLA) in New Mexico identified cold gas clouds thanks to the hydrogen line at 21 cm.
However, deep optical observations obtained with the MegaCAM instrument on the Canada-France-Hawaii Telescope (CFHT) revealed no evidence of star formation in these gas clouds. For the first time, these observations confirm the existence of dark gas clouds in filaments, as predicted by cosmological numerical simulations.
Benjamin Schneider, a postdoctoral fellow at the Laboratoire d’Astrophysique de Marseille (LAM) and formerly at the MIT Kavli Institute for Astrophysics and Space Research, was instrumental in analyzing the CFHT data and searching for possible optical counterparts to these gas clouds. His analysis confirmed the absence of star formation and reinforced the hypothesis that these clouds are probably located in dark matter halos within the filament. “This region of the sky attracted our attention thanks to the detection of a gamma-ray burst in one of the galaxies in the filament, although the link between this structure and this phenomenon remains anecdotal,” explains Benjamin Schneider.
A rare structure
This filament, 16 million light-years long and a few hundred thousand light-years wide, is one of the shortest and narrowest ever observed. Numerical cosmological simulations such as those of Millennium TNG show that such systems are predicted by current theoretical models, but are very rare. The team is making further observations and continuing to exploit numerical simulations to understand the origin of these unusual structures and their role in cosmic evolution.
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For further information:
-Press release from ORIGINS: https://www.origins-cluster.de/en/news-events/news/detail/necklace-of-dark-and-bright-pearls-on-a-striking-cosmic-filament
– The paper: https://iopscience.iop.org/article/10.3847/2041-8213/ada779
Caption:a cosmic filament with 8 figures (yellow). The Backround image is from the PanSTARSS survey. Illustration on the right show the position of dark gas cloouds, on the left the galaxy with a butterfly distribution of the gas (green). Credits: Arabsalmani et al (2025, 2022)
