The finding changes astronomers' views of how clusters and individual galaxies evolve. The colored image shows hot gas that lies between the galaxies. Yellow contour lines show the regions of radio emission, produced by shock waves in the gas as two clusters collided. Australia Telescope Compact Array. Composite image by Matteo Murgia, Istituto di Radioastronomia, Bologna, Italy.
Space is big.
Until now there has been only weak evidence that clusters might collide. The research was discussed Tuesday at a workshop on galaxy clusters at the Australia Telescope National Facility headquarters in Sydney. Clusters are big groups of galaxies, all held huddled together by gravity. Afterwards you see only ripples and bits of wreckage, but that's enough to show that there's been a collision. Radio arcs of the kind seen in this cluster are very rare.