Planck Discovers Huge Gas Filament Connecting Two Galaxy Clusters

European astronomers using ESA’s Planck Space Telescope have detected a 10 million light-years long bridge of hot gas connecting a pair of galaxy clusters, Abell 399 and Abell 401.

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.

Astronomers have already used the SZ effect to detect galaxy clusters themselves, but it also provides a way to detect faint filaments of gas that might connect one cluster to another.

The presence of hot gas between the billion-light-year-distant clusters Abell 399 and Abell 401 was first hinted at in X-ray data from ESA’s XMM-Newton, and the new data from Planck confirm the observation.

By combining the Planck data with archival X-ray observations from the German satellite Rosat, the astronomers have found temperature of the gas in the bridge to be similar to the temperature of the gas in the two clusters – on the order of 80 million degrees Celsius.

Early analysis suggests the gas could be mixture of the elusive filaments of the cosmic web mixed with gas originating from the clusters. These findings will be published in a paper in the journal Astronomy & Astrophysics (arXiv.org version).

A more detailed analysis and the possible detection of gas bridges connecting other clusters will help to provide more conclusive answers.

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Bibliographic information: P. A. R. Ade et al. 2012. Planck intermediate results. VIII. Filaments between interacting clusters. Accepted for publication in Astronomy & Astrophysics; arXiv: 1208.5911