Planck Spots Hot Gas Bridge Linking Galaxy Cluster Pair

A bridge of hot gas linking a pair of galaxy cluster across 10 million years of intergalactic space has been detected by ESA's Planck space telescope.

Planck was launched on 14 May 2009 and moved to an observing position more than a million kms from Earth on its "night side". It has two instruments of high and low frequency which observe the sky across nine frequency bands. The High Frequency Instrument (HFI) operates between 100 and 857 GHz, and the Low Frequency Instrument (LFI) operates between 30 and 70 GHz.

Planck has discovered a bridge of hot gas connecting the clusters Abell 399 and Abell 401, each containing hundreds of galaxies.

The goal of Planck's telescope is to capture the most ancient light of the cosmos, the Cosmic Microwave Background, or CMB.

While navigating through the Universe, it encounters different structures including galaxies and galaxy clusters. When the CMB light comes in contact with the hot gas permeating these huge cosmic structures, its energy distribution is modified in a characteristic way.

This phenomenon is termed as the Sunyaev-Zel'dovich (SZ) effect.  This effect causes a change in the apparent brightness of the Cosmic Microwave Background Radiation towards a cluster of galaxies or any other reservoir of hot plasma. Measurements of the effect provide distinctly different information about cluster properties than X-ray imaging data, while combining X-ray and Sunyaev-Zel'dovich effect data leads to new insights into the structures of cluster atmospheres.

This effect has been incorporated by Planck in order to detect galaxy clusters. In addition to this, it 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 was first hinted at in X-ray data from ESA's XMM-Newton, and the new Planck data confirmed the observation.

This is the first detection of inter cluster gas made by Planck with the help of SZ effect technique.

On combining Planck data with archival X ray observations from the German satellite Rosat, the temperature of the gas in the bridge is found to be similar to the temperature of the gas in the two clusters.

Based on early analysis it is predicted that the gas is a mixture of elusive filaments of the cosmic web mixed with gases originating from the clusters.