"(ScienceDaily July 5, 2012) A team of astronomers have used the United Kingdom Infrared Telescope (UKIRT) on Hawaii to discover four pairs of stars that orbit each other in less than 4 hours. Until now it was thought that such close-in binary stars could not exist. The new discoveries come from the telescope's Wide Field Camera (WFCAM) Transit Survey, and appear in the journal Monthly Notices of the Royal Astronomical Society.
About half of the stars in our Milky Way galaxy are, unlike our Sun, part of a binary system in which two stars orbit each other. Most likely, the stars in these systems were formed close together and have been in orbit around each other from birth onwards. It was always thought that if binary stars form too close to each other, they would quickly merge into one single, bigger star. This was in line with many observations taken over the last three decades showing the abundant population of stellar binaries, but none with orbital periods shorter than 5 hours.
For the first time, the team have investigated binaries of red dwarfs, stars up to ten times smaller and a thousand times less luminous than the Sun. Although they form the most common type of star in the Milky Way, red dwarfs do not show up in normal surveys because of their dimness in visible light.
For the last five years, UKIRT has been monitoring the brightness of hundreds of thousands of stars, including thousands of red dwarfs, in near-infrared light, using its state-of-the-art Wide-Field Camera (WFC). This study of cool stars in the time domain has been a focus of the European (FP7) Initial Training Network 'Rocky Planets Around Cool Stars' (RoPACS) which studies planets and cool stars..."