Reuters reports that astronomers have been able to see a clear separation between dark and ordinary matter, which answers a crucial question about whether dark matter interacts with itself other than via gravitational forces. "Dark matter makes up five times more matter in the universe than ordinary matter," Marusa Bradac of the University of California Santa Barbara, who led the work, said in a prepared statement. "This study confirms that we are dealing with a very different kind of matter, unlike anything that we are made of. And we're able to study it in a very powerful collision of two clusters of galaxies."
The Hubble images allowed the astronomers to infer the distribution of the total mass of both dark and ordinary matter in the cluster using a technique known as gravitational lensing. The dark matter can't be seen directly, but it has mass and therefore gravitational pull. Meanwhile, the Chandra X-ray images showed more clearly where ordinary matter, in the form of hot gas, was, reports Reuters. When the two clusters smashed together in a massive celestial crash, the hot gas in each cluster collided and slowed down--but the dark matter did not.
