Strange behavior in a huge cluster of merging galaxies could be explained if dark matter, the universe's most mysterious stuff, can collide with itself. [...] To get to the bottom of this mystery, researchers from the astrophysics and cosmology group of Italy's Scuola Internazionale Superiore di Studi Avanzati (SISSA) have started simulating what's happening in the massive galactic cluster 'El Gordo'
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