Astronomers discover a giant radio bridge connecting two galaxy clusters

A team of astronomers used deep radio observations from 53 MHz to 1.5 GHz with the LOFAR Low/High Band Antenna (LBA/HBA) arrays, the Jansky Very Large Array (JVLA) and the upgraded Giant Metrewave Radio Telescope (GMRT) and discovered the existence of a giant radio bridge connecting two pre-merging galaxy clusters A1758N and A1758S that are ~ 2 Mpc apart. This is the second large-scale radio bridge observed to date in a cluster pair. By studying the radio and X-ray emissions from the radio bridge, the astronomers found clear-cut evidence that the non-thermal phenomena in the intracluster medium (ICM) can be produced in the region of compressed gas in-between infalling systems.

Cluster Merger: Galaxy Clusters Caught in a First Kiss. Source: Chandra

The existence of radio bridges connecting pre-merging galaxy clusters has been confirmed very recently. Hitherto, only two such systems, namely A1758N-A1758S situated at a redshift of z = 0.279 and Abell 399-401 at z= 0.07 have shown to harbor a radio bridge between them. Interestingly, the study found remarkable commonalities between these large structures. Firstly, the mass of these galaxy clusters is enormous, with a virial mass greater than a hundred trillion times (10 to the power of 14) that of our Sun, and secondly, both of these cluster pairs lack dynamical stability. The study also confirms that these radio bridges occur only when the dissipation of energy takes place from dynamically active galaxy clusters.

The authors report that these large radio bridges can occur if electrons experience repeated accelerations through shock waves and turbulent motions between pre-merging clusters. This phenomena is known as Fermi acceleration and is thought to be the primary mechanism by which particles gain nonthermal energies in astrophysical shock waves. It plays a very important role in many astrophysical models, mainly of shocks including solar flares and supernova remnants.

Ths study also confirms for the first time that the ratio of energy emitted to that radiated (called emissivity) from these radio bridges is similar for both the radio bridges discovered to date and marks another similarity between these monstrous astronomical bridges.

The article has been published in Monthly Notices of the Royal Astronomical Society Letters.

Article Information: A. Botteon et al., "A giant radio bridge connecting two clusters in Abell 1758", MNRAS (L) 142, 2020.

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