New measurements of tiny galaxies contradict scientists' best model of dark matter, further complicating the already mysterious picture of the stuff that is thought to make up 98 percent of all matter in the universe. Dark matter, the invisible material thought to permeate the universe, can only be indirectly detected through its gravitational pull on the normal matter that makes up stars and planets. Despite not knowing exactly what dark matter is, scientists have gradually built up a good model to describe its behavior. The model envisions dark matter made up of cold, slow-moving exotic particles that clump together because of gravity.
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