Binary Star

Binary stars, often called double stars, refer to pairs of stars sufficiently close to each other in space to be gravitationally bound together. Following the laws of gravitation, each of the components revolves around the common center of mass of the system. At least 50% of stars are found to exist as binary systems, according to conservative statistics. There seems to be no obvious preference for particular combinations of brightness, size, or mass differences and a wide range in periods of revolution from less than a day to thousands of years. Likewise, there is a large range in separations from those stars in contact to those separated by thousands of times the Earth to Sun distance. Historically, visual binaries, those that appear as double stars when seen through a telescope, were discovered to be gravitationally bound by William Herschel around 1800.

There are a number of telescopic techniques used to discover and study binary stars. No one telescopic method can be used because of the wide range in the separations exhibited in the systems. The desired information about the orbital motion and the physical quantities of the stars themselves must come from different ways of observing. Hence, there are descriptive classifications of binary stars as determined by the various modes of study discussed below.