The dataset Tellis used for his study contained thousands of observations of stars as young as 200 million years and stars as old as nearly 10 billion years. Keck’s instruments collected millions of photons of light from these stars. What Tellis and his algorithm looked for were brief surges in photons. The first run of the data reported 5,000 potential candidates for mysterious laser beams, but they were eventually ruled out, explained away as emissions from stars’ outer layers, cosmic rays from our sun, or internal reflections from telescope instruments. Tellis got some firsthand Keck time to observe at least one target, KIC 8462852, a star about 1,500 light-years from Earth. In 2015, astronomers announced the Kepler space telescope had observed an unusual dimming of its light, which some believe could be caused by structures built by an advanced civilization around the star. The light emission observed from KIC 8462852 was the best candidate for an alien laser beam in the survey before it was ruled out.

The results may not have been surprising, but the method is noteworthy, says Jason Wright, an astronomer at Penn State University who contributed to some of the software code Tellis and Marcy used in the study. Recycling astronomical datasets that were produced for another purpose is pretty unusual, but it makes sense. There is strong competition among astronomers for observation time on the world’s best telescopes, and SETI proposals are usually low on the priority list.