One of the largest known stars in the universe underwent a dramatic transformation in 2014, new research shows, and may be preparing to explode. A study led by Gonzalo Muñoz-Sanchez at the National Observatory of Athens, published in Nature Astronomy today, argues that the enormous star WOH G64 has transitioned from a red supergiant to a rare yellow hypergiant—in what may be evidence of an impending supernova.