When neutron stars merge, as illustrated here, they produce a gravitational-wave signal from their inspiral and a host of spectrum-spanning electromagnetic signatures from before, during, and after the collision. Telescopes on the ground and in space detected such signatures in August 2017 hours after a gravitational-wave detection by the LIGO and Virgo observatories. Read our AAS Nova article on a study published in the Astrophysical Journal Letters on how such alerts might go out sooner, enabling more timely follow-up observations. [NSF, LIGO, Sonoma State Univ., A. Simonnet]