As odd couples go, it’s tough to beat the stellar pair at the heart of R Aquarii. This symbiotic binary system comprises a cool red giant and a sizzling white dwarf locked in a 44-year elliptical orbit. The enormous star pulsates in a roughly 390-day period, driving changes in temperature and brightness. It has only a tenuous grasp on its bloated outer layers, which allows the white dwarf to siphon some of this material when the two come closest. The liberated hydrogen forms an accretion disk around the white dwarf. When enough gas accumulates, it triggers an outburst that creates the surrounding nebula. At a distance of some 700 light-years, R Aqr ranks as the closest symbiotic binary to Earth. This image combines X-ray data (purple) and visible-light observations (red, orange, blue, and violet).
