Magnetic Map of the Intergalactic Bridge express
Two giant galaxy clusters, Abell 3391 and Abell 3395, are slowly colliding in the southern sky. Between them stretches a bridge of scorching gas, like a mist over a river, linking two banks. Astronomers have long wanted to know whether this "intergalactic bridge" hosts a magnetic field and how it behaves.
The field cannot be seen directly, but its trace can be caught. When radio waves from distant galaxies pass through magnetized gas, their plane of oscillation rotates slightly — an effect known as Faraday rotation. The stronger and more tangled the field, the greater the rotation. The astronomers aimed the MeerKAT radio telescope in South Africa at this region, collected signals from 434 distant galaxies, and built a magnetic field map from their rotations.
This contrast hints that the field in the bridge is not just present: it is aligned by some process. Perhaps gas flows streaming between the clusters stretch and straighten the magnetic field lines, much as a river aligns seaweed with the current. In the clusters themselves, the field is constantly shaken: hot gas churns, supernovae explode, and black holes at the centers of galaxies are active.
Such a "magnetic bridge" between clusters is a rare stroke of luck for astronomers. It offers a glimpse of how magnetic fields behave on the largest scales — where individual galaxies no longer matter, and only the cosmic web counts. Understanding these fields will help explain how giant structures grow and why charged particles in space move the way they do.
The density of "background" galaxies used as probes reached 110 per square degree at the center of the field of view, as if a whole crowd of distant radio sources were packed into an area the size of a fingernail at arm's length.