Massive Merger of Galaxies is Most Powerful on Record

In 2004, an international team of scientists, led by a NASA-funded researcher, observed a nearby head-on collision of two galaxy clusters. The clusters smashed together thousands of galaxies and trillions of stars. It is one of the most powerful events ever witnessed. Such collisions are second only to the Big Bang in total energy output.

The event was captured with the European Space Agency's XMM-Newton observatory. Scientists are calling the event the perfect cosmic storm: galaxy clusters that collided like two high-pressure weather fronts and created hurricane-like conditions, tossing galaxies far from their paths and churning shock waves of 100-million-degree gas through intergalactic space. The cluster, Abell 754 in the constellation Hydra, has been known for decades. However, the new observation reveals the merger may have occurred from the opposite direction than was previously thought.

This unprecedented view of merger in action crystallizes the theory the universe built its magnificent hierarchal structure from the "bottom up," essentially through mergers of smaller galaxies and galaxy clusters into bigger ones.

Galaxy clusters are the largest gravitationally bound structures in the universe, containing hundreds to thousands of galaxies.

See http://www.nasa.gov/centers/goddard/news/topstory/2004/0831galaxymerger.html