Data from Gemini North and the GTC showing the decreasing orbital period of J0651

Data from Gemini North and the GTC showing the decreasing orbital period of J0651. The dotted lines shows when the eclipse times should occur if the orbit were constant. The top panel shows how the eclipses have changed from when expected; the dashed line fits the observations. The bottom panel shows a zoomed view of the primary eclipses for four different months of observations (the colors correspond to the points in the top panel). Over time, the mid-point of the eclipses happen sooner (they shift to the left), indicating that the orbital period of the binary system is shrinking. The rate at which this orbit is shrinking is so far consistent with predictions from the emission of gravitational waves.