Shocks during galaxy cluster merger
When two galaxy clusters merge, theoretical models and numerical simulations predict that the first contact between the hot gas halos associated with each cluster (shown here in pink and violet) creates shock waves that propagate outwards along the equatorial plane of the merger (shown in red). Then, as the merger proceeds, additional shocks form and propagate along the merger axis (shown in blue). The latter type of shocks has been observed in many merging clusters, whereas equatorial shocks were first detected in the merging pair of galaxy clusters 1E2216 and 1E2215.
While the pre-merger phase lasts for a relatively short period of time – around 100 million years – the entire merging process takes billions of years to complete.
The observation of shock waves propagating along the equatorial plane in the hot gas within 1E2216 and 1E2215 indicates that the two clusters are seen while coming into contact for the very first time – something that has never been observed before.