Galaxy clusters are the largest known objects bound by gravity, and as the name suggests consist of hundreds of galaxies, each containing billions of stars.

Due to their size, which measures in the millions of light years, the collision of two galaxy clusters takes around a billion years to complete, meaning the first stage when the clusters touch is a relatively short and rare moment to witness.

"Merging galaxy clusters have been observed many times in various stages of the merger process but this is the first time we clearly observe one in which two large subclusters are just about to merge," Dr. Huib Intema from Western Australia's Curtin Institute of Radio Astronomy told Xinhua.

"This observation provides the first clear view on what happens just before two large clusters merge, and allows us to study how the potential energy released in the merger is affecting and shaping the newly-to-be-formed larger cluster."

Computer simulations show that in the first moments before clusters touch, an immense shockwave of 100-million-degree gas is released, a theory which has been predicted but evidence of which is only now being revealed.

"X-ray and radio images of these clusters show the first clear evidence for this type of merger shock," lead author Liyi Gu from Japan's RIKEN research institute said.

"The shock created a hot belt region of 100-million-degree gas between the clusters, which is expected to extend up to, or even go beyond the boundary of the giant clusters."

Scientists intend to build up a collection of "snapshots" documenting the clusters' progress to increase understanding of collisions.