A cosmic multimessenger gold rush

Direct detection of gravitational waves (GWs) from black hole (BH) mergers began in earnest in 2015, but until this August, astronomers hunting for electromagnetic (EM) counterparts to GW events were left in the dark. Published in Science 's First Release this week, Kasliwal et al. ( 1 ), Evans et al. ( 2 ), Hallinan et al. ( 3 ), and Coulter et al. ( 4 ) detail the exciting search and discovery of a panchromatic transient, dubbed EM170817, which they argue is the first unassailable EM counterpart to a GW event. That event (GW170817) was promptly recognized by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo collaboration ( 5 ) as resulting from the merger of two neutron stars (NSs), compact stellar remnants about 40% more massive than the Sun but only a few kilometers in radius. The reported observations, connecting GWs to both gamma-ray bursts (GRBs) and a long-theorized—but hitherto undetected—short-lived EM transient represents a watershed moment in astrophysics.