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Planet Hunters (https://www.planethunters.org) is a citizen science effort to search for planets by analyzing publicly available data from NASA’s Kepler mission. Launched in 2009, Kepler detects planets by monitoring the slight decrease in a star’s light flux as an orbiting planet transits in the line of sight. In September 2015, the Planet Hunters announced an unusually pronounced and long dimming event associated with the star KIC 8462852, also named Boyajian’s star for the lead author of the report (Fig. 1) [1]. A transiting planet couldn’t have caused the dimming; most explanations instead involved other larger objects orbiting around the star. Some researchers even speculated that these bodies could be alien megastructures like energy-harvesting solar panels. None of these ideas, however, have satisfactorily explained the observed dimming, which remains a major astronomical mystery.

Now, a useful clue towards solving this puzzle has been offered by Mohammed Sheikh, Richard Weaver, and Karin Dahmen from the University of Illinois at Urbana–Champaign [2]. The researchers analyzed the spectrum of fluctuations in the flux from Boyajian’s star over four years, finding that it followed a universal power-law characteristic of systems close to the critical point of a phase transition. While this result does not reveal the physical processes driving the brightness variations, it suggests that they might be associated with nonequilibrium phenomena occurring within the star, rather than with external orbiting structures.

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