The Dark at the Center of a Cosmic Collision

The Abell 520 galaxy cluster is an unusual structure resulting from a major merger of far off galaxies. It has been popularly nicknamed “The Train Wreck Cluster”, due to its chaotic structure. Five years ago, SF State researcher Andisheh Mahdavi and his colleagues observed an unexpected dark core at the center of Abell 520, a cosmic “train wreck” of galaxy clusters. With new space-based telescope observations, they have confirmed that the core really does exist. But they are no closer to explaining why it is there. When galaxy clusters crash into each other, the bright matter of galaxies sticks together with the mysterious substance called dark matter, leaving behind hot gases. Or at least that is what astronomers have observed in similar cosmic wrecks like the Bullet Cluster. But Myungkook James Jee of the University of California, Davis, Mahdavi and their colleagues say Abell 520 has a definite — but bewildering — dark matter core that is completely separated from its usual bright partners.

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