For more than two decades, astronomers have been systematically tracing mystery sources of high-energy gamma rays to their sources. One, however, remained stubborn - the brightest unidentified source of gamma rays in the Milky Way. It seemed to be coming from a binary system 2,740 light-years away, but only one of the stars could be found. Now, astronomers have solved the mystery and pinned down that second star by searching gamma-ray data obtained between 2008 and 2018. Together, the two stars constitute one of the weirdest binary systems we've ever seen. "The binary star system and the neutron star at...