Plasma effects on fast pair beams in cosmic voids

Summary form only given. Intergalactic space is transparent to radiation in most of the electromagnetic spectrum. However, gamma-rays above GeV energies cannot travel cosmological distances as they are converted into electron-positron pairs, e ± , by way of photon-photon interactions with the extragalactic background light (EBL). Each particle of the gamma-ray produced e ± pair, if not modifed by plasma effects, on a typical length scale 1 IC ∼ 30 kpc, inverse Compton scatters on the cosmic microwave background radiation, initiating a full electromagnetic cascade. However, the initially created pair beam is subject to two-stream-like instabilities of both electrostatic and electromagnetic nature, which may completely prevent the electromagnetic cascade.