Astronomers have found a bridge of gas extending over three million light-years from two galaxy clusters in the system known as Abell 2384.

The clusters collided several hundred million years ago, then passed through each other to arrive in their current configuration. This released a large amount of hot gas that now spans the distance between them.

This superheated bridge glows brightly in X-rays, and was detected by NASA’s Chandra X-ray Observatory, ESA’s XMM-Newton, and the Giant Metrewave Radio Telescope in India. 

The new multi-wavelength view of Abell 2384 above is a composite of images from all three telescopes. 

It shows the effects of a jet shooting away from a supermassive black hole in the centre of a galaxy in one of the clusters. The jet is so powerful that it is bending the shape of the bridge, which has a mass of about six trillion suns.

A labelled version of the image (right) traces the shape of the bridge, marks the position of the supermassive black hole, and shows where the jet is pushing the hot gas in the bridge sideways at the collision site. 

The lobe of radio emission marking the end of each jet is also shown. 

At the collision site, a research team from South Africa, Brazil, India and France found evidence for a shock front, similar to a sonic boom from a supersonic aircraft, which can keep the gas hot and prevent it from cooling to form new stars.

The radio emission extends about 1.2 million light-years from the black hole to the north and about 1.7 million light-years to the south. 

The northern radio emission is also fainter than the southern emission. These differences might be explained, the researchers say, by the radio emission to the north being slowed down by the jet’s impact with the hot gas in the bridge.

A paper describing this work has been published in the Monthly Notices of the Royal Astronomical Society. It is available on the pre-print server arXiv.

Chandra has often observed cavities in hot gas created by jets in the centres of galaxy clusters – such as the Perseus cluster, MS 0735 and the Ophiuchus cluster – but Abell 2384 is a rare case of such an interaction occurring in the outer region of a cluster. 

It also is unusual that the supermassive black hole driving the jet is not in the largest galaxy located in the centre of the cluster. 

Based on computer simulations, it has been shown that after a collision galaxy clusters oscillate like a pendulum and pass through each other several times before merging to form a larger cluster. Astronomers thus think the two clusters in Abell 2384 will eventually merge.

The system is located 1.2 billion light-years from Earth. Based on previous work, scientists estimate its total mass 260 trillion times that of the Sun. This includes the dark matter, hot gas and the individual galaxies.