Astronomers using data from the Chandra X-ray Observatory and other telescopes have put together a detailed map of a rare collision between four galaxy clusters. 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 in the cosmos that are held together by gravity. Clusters consist of hundreds or even thousands of galaxies embedded in hot gas, and contain an even larger amount of invisible dark matter. Sometimes two galaxy clusters collide, as in the case of the Bullet Cluster, and occasionally more than two will collide at the same time.

The new observations show a mega-structure being assembled in a system called Abell 1758, located about 3 billion light-years from Earth. It contains two pairs of colliding galaxy clusters that are heading toward one another. Scientists first recognized Abell 1758 as a quadruple galaxy cluster system in 2004 using data from Chandra and XMM-Newton, a satellite operated by the European Space Agency (ESA).  

X-rays from Chandra are shown as blue and white, depicting fainter and brighter diffuse emission, respectively. This new composite image also includes an optical image from the Sloan Digital Sky Survey. The Chandra data revealed for the first time a shock wave — similar to the sonic boom from a supersonic aircraft — in hot gas visible with Chandra in the northern pair’s collision. From this shock wave, researchers estimate two clusters are moving about 2 million to 3 million miles per hour (3 million to 5 million kilometers per hour), relative to each other.

The team also used radio data from the Giant Metrewave Radio Telescope (GMRT), and X-ray data from the European Space Agency’s XMM-Newton mission.

Image Credit: X-ray: NASA/CXC/SAO/G.Schellenberger et al.; Optical:SDSS