Some of the universe's dark matter was found to be tied up in really small, nearby galaxies that researchers dubbed "hobbit galaxies." Each contains only a few stars but has a mass about 100 times more than what would be expected from the mass of their stars alone. The hidden stuff, noted by its gravitational effects, must be invisible material that astronomer call dark matter. In separate work, astronomers made a 3D map of dark matter across a big swath of space and time. Of course, nobody knows what the heck dark matter is.