50 million light-year long gas filament discovered, confirming model of the evolution of the Universe

New research published today in the journal Astronomy & Astrophysics describes the discovery of the longest gas filament yet seen. At 50 million light years long, this thread of hot gas stretches between two vast clusters of galaxies that are in the process of merging together. This discovery strikingly resembles predictions from computer simulations about how structure in the Universe should appear and confirms the understanding of the way the Universe has evolved.

This study used data from the eROSITA space telescope and CSIRO’s ASKAP radio telescope in Western Australia. The x-ray measurements from eROSITA are sensitive to the hot gas present in the galaxy clusters, while the ASKAP radio data pick out emission associated with galaxies and arising from extended energetic jets powered by supermassive black holes within those galaxies. Combining the data from both facilities allows a unique perspective on the complex interplay between gas and galaxies in this system of merging galaxy clusters.

For many years we have known about the relationship between gas in galaxy clusters and the way the galaxies themselves influence and are influenced by such hot gas. In particular, the radio jets from galaxies with supermassive black holes are known to be able to push the hot gas within a cluster aside as they shoot out into space. The novel discovery with these latest observations arises from the unique nature of the extended hot gas filament. These kinds of structure have been predicted in the best current models of the Universe, but this is the first time such a clear example has been discovered.

The ASKAP telescope was able to image the entire merging cluster system in a single exposure due to the extremely large field of view of its Phased Array Feed (PAF) technology. The highly sensitive radio image spanning the entirety of this complex galaxy system has enabled the identification of many extended radio structures, associated with supermassive black holes. The way this extended radio emission is distorted in the comparatively dense cluster gas as these galaxies fall into the clusters helps to identify which way they are moving and in turn trace the gravitational influence of the complex cluster pair. This information adds evidence for the way such structures evolve, in support of the underlying model of the Universe.

Almost 50 scientists from institutions in Germany, Australia, the USA, Switzerland, Chile, Spain, South Africa and Japan participated in the study, led by Prof. Thomas Reiprech at the University of Bonn. The eROSITA telescope is a joint German-Russian facility, developed with funding from the Max Planck Society and the German Aerospace Center (DLR), and launched into space last year on board a Russian-German satellite whose construction was supported by the Russian space agency Roskosmos. The ASKAP telescope was developed by CSIRO and is sited at the Murchison Radio Observatory in Western Australia. Its novel PAF technology enables it to rapidly deliver extremely sensitive radio images over large areas of the sky.

The ASKAP measurements in this investigation were taken as part of the "early science observations" for a project called the Evolutionary Map of the Universe, also known as ‘EMU’, one of nine major survey programs planned with ASKAP. EMU is an international collaboration of over 400 scientists, led by Professor Andrew Hopkins at Macquarie University, who participated in this study. The success of these preliminary observations is a positive sign for the full project, expected to start in late 2021, which will map the entire Southern Hemisphere, an area about 1000 times as large as covered here, and with even better sensitivity. 


Figure 1: Optical image of the Abell 3391/95 system taken with the DECam camera. Superimposed are the eROSITA image (darker = higher gas density) and radio contours (yellow) of the ASKAP telescope.
© Reiprich et al., Astronomy & Astrophysics

Author: Prof. Andrew Hopkins, Macquarie University