Sunyaev–Zel'dovich effect

A change in cosmic microwave background radiation caused when its photons scatter from energetic electrons, especially in galaxy clusters.

Inverse Compton scattering: A scattering process in which energetic charged particles transfer energy to photons. It is the underlying process that boosts cosmic microwave background photons in the thermal effect.
Galaxy cluster: A gravitationally bound system containing hundreds to thousands of galaxies, hot gas, and dark matter. Clusters supply the dense hot plasma that produces a strong signal.
Cosmic microwave background: Relic radiation from the early universe, now observed as a nearly uniform microwave glow. It provides the photons whose spectrum and temperature the effect changes.
Thermal bremsstrahlung: Radiation emitted when charged particles accelerate in the electric fields of other charged particles. It produces the cluster's X-ray emission, unlike the microwave distortion from scattered background photons.
Thermal Sunyaev–Zel'dovich effect: The spectral distortion produced when hot electrons transfer energy to cosmic microwave background photons. This is the dominant cluster signal from random thermal motions of electrons.
Sunyaev–Zel'dovich cluster survey: An astronomical survey that detects galaxy clusters through their microwave scattering signal. These surveys find massive clusters across a broad range of distances.
Intracluster medium: The hot, diffuse plasma occupying the space between galaxies in a galaxy cluster. Its free electrons scatter the background radiation throughout a cluster.
X-ray astronomy: The study of celestial objects through their X-ray emission. X-rays measure gas density and temperature, complementing the effect's line-of-sight pressure signal.
Kinematic Sunyaev–Zel'dovich effect: A cosmic microwave background temperature shift caused by the bulk motion of scattering electrons. It isolates the line-of-sight motion of cluster gas rather than its heat.
Cluster cosmology: The use of galaxy-cluster populations and properties to constrain cosmological parameters. The effect helps select clusters for tests of structure growth and cosmic expansion.

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