2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/2355Plasma containing relativistic particles appears in various forms in the inter galactic medium (IGM): As radio plasma released by active radio galaxies, as fossil radio plasma from former radio galaxies - so called `radio ghosts', as `cluster radio relics' in some clusters of galaxies, and as `cluster radio halos'. The impact of the different forms of radio plasma on the IGM and their use as diagnostic tools are briefly discussed.4 pages, to appear in the Proccedings of the `4th China-Germany Workshop on Cosmology', uses ws-p9-75x6-50.cls (included)Astrophysicstext