Astronomers spot the "crest" of plasma connecting galaxy clusters

Groups of galaxies are a great place to observe the physics that governs our universe. These cosmic hotspots harbor hundreds, if not thousands, of galaxies, but they also contain a mine of hot gas and dark matter. And when clusters of galaxies merge, the fireworks can really begin.

A team of astronomers led by Federica Govoni of the Italian National Institute of Astrophysics has for the first time discovered a "peak" of plasma-emitting radio waves connecting two galaxy clusters being merged: Abell 0399 and Abell 0401 The ridge, which is part of the cosmic network along which clusters of galaxies tend to congregate, stretches for about 10 million light-years and presents evidence of a magnetic field and relativistic particles – electrons moving at a speed close to that of light. Their work will be published on June 7 in Science.

Follow the clues

The cosmic canvas looks exactly like what it looks like: gaseous hydrogen filaments resembling a spider's web extend into the universe. Astronomers believe that the cosmic web traces the distribution of dark matter, which can only be detected by gravitational attraction. Clusters of galaxies tend to congregate at the intersections of these filaments, making them extremely interesting places to study.

Govoni's team had already discovered traces of magnetic fields in both groups during previous work. Observations with the Plank satellite of the European Space Agency had also uncovered a hot plasma filament – part of the cosmic network – also linking clusters. With these two facts in hand, Govoni's group questioned whether magnetic fields could extend along the plasma filament, perhaps also connecting the two groups.

To investigate, the team used the Low Frequency Network (LOFAR), a network of radio telescopes in the Netherlands. Based on their observations with LOFAR, the team spotted a "weak, diffuse and extensive radio source" between the clusters, Govoni said in a video associated with the press release. "It's a direct proof of the presence of magnetic fields and relativistic particles in the filament connecting these two systems," she added. Based on simulations modeling their results, the team concluded that the ridge had a magnetic field about a million times lower than that of the Earth.