This image shows galaxy clusters Abell 399, lower center, and Abell 401 connected by a bridge of hot gas (ESA Planck Collaboration / STScI Digitized Sky Survey)

 Planck’s primary task is to capture the most ancient light of the
cosmos. If this faint light interacts with the hot gas permeating
different types of space structures including galaxies and galaxy
clusters, its energy distribution is modified in a characteristic way, a
phenomenon known as the Sunyaev-Zel’dovich (SZ) effect. See: Planck Discovers Huge Gas Filament Connecting Two Galaxy Clusters

Astronomy & Astrophysics; arXiv: 1208.5911

See Also:

• Thoughts on Dark Matter Search

•  It Starts with a Bang

•  Merging Galaxy Cluster Abell 520