The Universe is not distributed uniformly. Galaxies are arranged in a gigantic cosmic web made of voids, filaments, and galaxy clusters. These filaments act as enormous “cosmic highways” through which matter and galaxies flow toward the densest regions of the Universe. Understanding how these structures influence galaxy evolution is one of the major goals of modern astrophysics.
In this work, we analyzed hundreds of thousands of galaxies from the Sloan Digital Sky Survey (SDSS) to study how galaxy density changes around cosmic filaments in the nearby Universe. Our main goal was to determine how far the physical influence of filaments extends into their surrounding environments.
Our results show that the influence of cosmic filaments reaches distances of up to about 10 megaparsecs (roughly 30 million light-years) from their central spine. We also found that the densest regions are concentrated within the inner core of the filaments, inside approximately 1 Mpc (about 3.3 million light-years). This means that galaxies approaching filaments experience gradual environmental transformations long before they enter massive galaxy clusters.
The study also provides, for the first time observationally in this redshift range, evidence that filaments evolve with cosmic time. Filaments observed around 4 billion years ago appear broader and less concentrated than those in the local Universe today. This suggests that filaments continue to collapse gravitationally and become more compact even at relatively recent epochs in cosmic history.
These findings are important because they help us understand how the large-scale cosmic environment affects fundamental galaxy properties such as star formation, morphology, and gas content. The work provides new evidence that galaxy transformation processes begin already within the filaments of the cosmic web, and not only after galaxies enter massive clusters.
