A radio ridge connecting two galaxy clusters in a filament of the cosmic web
A radio ridge between two galaxy clusters Galaxy clusters contain dozens or hundreds of galaxies, vast quantities of hot gas, and large amounts of dark matter. The gas can emit at radio wavelengths if it contains electrons at relativistic speeds, which can be injected by active galaxies or accelerated during a merger between two clusters. Govoni et al. used the Low-Frequency Array (LOFAR) radio telescope to observe a ridge of radio-emitting plasma extending between two galaxy clusters that are approaching a merger. The results imply that intergalactic magnetic fields connect the two clusters and challenge theories of particle acceleration in the intergalactic medium. Science, this issue p. 981 A ridge of low-frequency radio emission connects two galaxy clusters that are approaching a merger. Galaxy clusters are the most massive gravitationally bound structures in the Universe. They grow by accreting smaller structures in a merging process that produces shocks and turbulence in the intracluster gas. We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low-Frequency Array (LOFAR) telescope network at 140 megahertz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may reaccelerate a preexisting population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge.