Dark matter: the universe has gotten lumpier

Four-fifths of the matter in the universe is invisible. Nevertheless, this “dark matter” will determine the fate of the cosmos. But how is it distributed? That can be determined by measuring its gravitational effects. Gravity also changes the path that light takes as it travels from distant galaxies. The Hyper Suprime-Cam (HSC) of the Japanese Subaru telescope has studied these effects for approximately ten million galaxies. The farther away a galaxy is, the longer it takes its light to reach...