Radio halo

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This article is about the astronomical phenomenon. For the geological phenomenon see radiohalo.

Radio halos are large-scale areas of radio emission found in clusters of galaxies. They do not have an obvious galaxy counterpart, as opposed, for example, to radio galaxies which have AGN counterparts. Their cause is still debated, but they may come to exist due to turbulence created when two clusters of galaxies collide. They are found at the centre of clusters. Radio relics are similar features found at the edge of clusters.

They are likely to result from synchrotron radiation originating from electrons, moving in the intracluster magnetic field of around 1 - 10 μ G.