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Astronomers have detected a ‘missing link’ shockwave in merging galaxies

The colossal shock wave generated by the early stages of a collision between some of the most massive structures in the Universe has just been seen and imaged for the first time.

The detection was found in the galaxy cluster Abell 98, which is a large structure made up of three smaller galaxy subclusters located more than 1.2 billion light-years from the solar system.

There, a huge filament of gas contains the huge shock along the fusion axis that has been theoretically predicted to be the first “contact” between two galaxy subclusters as they begin to merge.

“With this discovery, we have captured two subclusters of a galaxy cluster at a crucial early epoch in the merging process, with a strong clash between them, providing a missing link to the formation of the most massive structures in our universe. “, said physicist and astronomer Arnab Sarkar from the University of Kentucky.

Pressure measurement through the shock wave in Abel 98. (Arnab Sarkar)

The Universe is constantly interacting with itself and organizing itself. Galaxies are not isolated entities drifting through space; gravity is everywhere, and the constant push-pull and interaction results in clusters and superclusters and megaclusters and filamentdancing around each other and forming bigger and bigger structures.

These interactions do not, of course, occur on anything that remotely approaches human time scales; but, by observing clusters in different stages of melting, astronomers can reconstruct how these collisions occur.

Within galaxy clusters, as you can imagine, the gravitational environment is quite intense, with subclusters merging to form larger structures within the overall cluster.

In 2014, astronomers have noted that two sub-clusters within Abell 98 – named A98N and A98S – appeared to merge, as evidenced by luminosity and temperature signatures in A98N consistent with a fusion shock between the two.

Sarkar and his team, who presented their findings at the 240th meeting of the American Astronomical Societytook a closer look at the region between the two subgroups using Earth orbit Chandra X-ray Observatory. There they found what they describe as “definitive evidence” of a shock edge south of A98N.

This, they say, is a huge deal. While inter- and intra-cluster mergers must be fairly common (because, well, the Universe is full of galaxy clusters), catching one in its early stages is fairly rare. We see a lot of it in the later stages, including the shock waves generated by these extreme interactions, but very little as the clusters come together.

This may be because they are harder to spot, but the detection made by Sarkar and his colleagues may inform future research by providing information on what to look for. And, of course, it fills in some of the crucial gaps in our understanding of how cluster mergers happen and evolve. This means that we will be able to make better predictions about the evolution of galaxy clusters.

“This result is important because different computer simulations seem to be telling us different things about what we should observe at the onset of a galaxy cluster merger,” he added. Sarkar said. “Here we have a picture of what that process actually looks like, and that can be used to inform our theoretical models.”

The team’s research was presented at the 240th meeting of the American Astronomical Society. A document describing the results has been submitted to The Astrophysical Journaland is available at arXiv.