Astronomers using the XMM-Newton Observatory have witnessed the most powerful collision of galaxies yet seen that sent 100-million-degree gas spewing through space. With an energy output that is second only to the big bang, the event has been dubbed the "perfect cosmic storm." What was once two distinct but smaller galaxy clusters 300 million years ago is now one massive cluster in turmoil, remarks team leader Patrick Henry of the University of Hawaii.

The roiling cluster studied by Henry and his colleagues is known as Abell 754 and is located some 800 million light-years from Earth. The data collected by the team using the space-based X-ray observatory is the most detailed look yet at how cosmic objects merge, boosting the idea that our universe built itself from the bottum up through collisions of smaller objects to form larger ones, resulting in the hierarchal structure seen today. By tracing the movement of the wreckage of the collision, the scientists revealed the paths taken by the two smaller clusters, one containing some 300 galaxies, the other closer to 1,000. "One cluster has apparently smashed into the other from the 'north-west' and has since made one pass through," explains team member Alexis Finoguenov of the Max Planck Institute for Extraterrestrial Physics in Germany. "Now, gravity will pull the remnants of this first cluster back toward the core of the second.

The team collected enough data on Abell 754 to compile a current map of its conditions, including temperature, pressure and density, as well as propose a weather forecast. Explains Finoguenov, Over the next few thousand million of years, the remnants of the clusters will settle and the merger will be complete." The researchers describe their results in a paper that will appear in an upcoming issue of the Astrophysical Journal.