A Tour of a Collision Between Four Galaxy Clusters in Abell 1758

Narrator (April Jubett, CXC): When two pairs of galaxy clusters collide, the final result is not four separate objects, but one giant galaxy cluster. Astronomers using data from NASA's Chandra X-ray Observatory and several other telescopes have put together a detailed map of a rare collision between four galaxy clusters.

This mega-structure is being assembled in the system called Abell 1758 located about 3 billion light years from Earth. Eventually all four clusters — each with a mass of at least several hundred trillion times that of the Sun — will merge to form one of the most massive objects in the Universe.

Galaxy clusters are the largest structures held together by gravity. They consist of hundreds or even thousands of galaxies embedded in hot gas, and contain an even larger amount of unseen dark matter that gravitationally dominates the cluster. Sometimes two galaxy clusters collide, as in the case of the Bullet Cluster, and occasionally more than two will collide in the same timeframe.

The Chandra data revealed for the first time a shock wave — similar to the sonic boom from a supersonic aircraft — in hot gas in the northern pair's collision. From this shock wave, researchers of the new study estimated one pair of clusters are moving relative to each other, at a speed between two and three million miles per hour.

Chandra also provides information about how elements heavier than helium in the clusters' hot gas get mixed up and redistributed after galaxy clusters collide and merge. Because this process depends on how far a merger has progressed, Abell 1758 offers a valuable case study, since the two pairs of clusters are at different stages of merging. The new Abell 1758 result shows the further along a merger is, the farther away from the centers of the clusters these important heavy elements are found.