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. The first ones found were thought to be ghostly remains of dead, dissipated galaxies, and were dubbed 'relics', Ms Johnson-Hollitt explains. Professor Ron Ekers is one of the people who worked on the first known examples of these objects. Theorists had predicted that galaxy clusters would free-fall together at thousands of kilometres a second, smacking into each other and producing huge shock waves in the thin hot gas that fills the space between the galaxies.