Millions of years ago two massive stars circled each other in a cosmic dance. Then one of the stars went supernova. The blast likely flung the exploded star’s companion across space, setting it adrift in the cosmos for tens of thousands of years before it, too, succumbed to the same explosive end. That, at least, is what astronomers believe may have happened to a newly identified pair of stellar remnants. Using observations from NASA’s Fermi Gamma-ray Space Telescope, researchers suggest that...