Previous instruments (e.g., ROSAT, ASCA) did not have the capabilities of Chandra and XMM-Newton (two current X-ray observatories) and were unable to map the region in detail.

"Now we can begin to understand the physics of these mergers, which are among the most energetic events in the universe," said Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, and leader of the international team involved in the analysis of the observations.

"The pressure and density maps of the cluster show a sharp boundary that can only exist in the moving environment of a merger.

"[1] A2142's observed X-ray emissions are largely smooth and symmetric, suggesting it is a result of a merger between two galaxy clusters viewed at least 1–2 billion years after the initial core crossing.

One would expect to observe uneven X-ray emission and obvious shock fronts if the merger was at an early stage.