Astronomers using the eROSITA X-ray telescope have detected an intergalactic filament stretching nearly 50 million light-years—the longest ever observed.
The Universe's matter distribution forms a vast cosmic web, with galaxy clusters at nodes connected by enormous filaments of hot gas. These structures hold more than half of all baryonic matter—the stuff that forms stars, planets, and us. A new study published in Astronomy & Astrophysics details one such filament.
These filaments are incredibly tenuous, with just ten particles per cubic meter, making them challenging to detect. Researchers from the University of Bonn, Germany, turned to the eROSITA X-ray telescope, developed by the Max Planck Institute. "eROSITA's detectors are highly sensitive to the X-rays emitted by this hot gas," explains lead author Thomas Reiprich. "Its wide field of view captures large sky areas at high resolution in a single observation."
The team targeted the Abell 3391/95 system, featuring three galaxy clusters located 700 million light-years from Earth. eROSITA resolved the clusters, their galaxies, and two connecting gas filaments—one measuring 49 million light-years, the record holder to date.
These findings align closely with the team's cosmological simulations tracing the Universe's evolution. "eROSITA images strikingly match our computer models," notes Reiprich, "validating the standard model of cosmic development."
