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.
