Serendipitous observation of merging stars could explain rare novae

Nature : Two years ago a rare red nova, dubbed V1309 Scorpii, appeared in a part of the sky being monitored by the Optical Gravitational Lensing Experiment (OGLE) in Chile. Unlike the more common blue novae, which correspond to thermonuclear explosions on white dwarfs, red novae are more mysterious. Now, having examined data taken before V1309 Scorpii’s flare-up, the OGLE team has determined its cause: the merger of two stars that had been orbiting each other so closely that their atmospheres overlap. Such orbits inevitably shrink as the overlapping atmospheres drain orbital energy from the binary system. Nature‘s Ken Croswell describes the serendipitous discovery.