The collision of two neutron stars (GW170817) flung out an extraordinary fireball of material and energy that is allowing a a team of astrophysicists to calculate a more precise value for the Hubble constant, the speed of the universe's expansion. Previous estimates put the value between 66 and 90 km/s/Mpc, which this team refined to between 65.3 and 75.6 km/s/Mpc.