Sunyaev–Zel'dovich effect

The Sunjajew - Seldowitsch effect (. According to Rashid Sunyaev and Yakov Borisovich Seldowitsch; engl transcription: Sunyaev - Zel'dovich effect, abbreviation SZ effect) describes the reduction in the number of low-energy photons and increasing the number of higher-energy photons relative to the Planck spectrum of the cosmic background radiation in hot gas in galaxy clusters.

The electrons in the intracluster medium, the hot ionized part of the intergalactic medium of a galaxy cluster, contained are able to scatter photons of the cosmic background radiation. By inverse Compton effect energy is transferred from the electrons to photons in the middle, the frequency is increased accordingly. This leads to a shift in the relative number of low energy to high-energy photons compared to the original Planck spectrum.

With the help of the SZ effect can detect, among other galaxy clusters, which are visible as "shadows" in front of the uniform spectrum of the cosmic background. The measurement of Sunjajew - Seldowitsch effect and the search for distant galaxy clusters is one of the objectives of the Planck mission.