Strange behavior in a massive 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 conundrum, researchers from the Astrophysics and Cosmology group of Italy's Scuola Internazionale Superiore di Studi Avanzati (SISSA) set about simulating what is happening within the massive galactic cluster " El Gordo "
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