There is a huge range of scale in binary star orbits and consequently the period can, at the longer end, reach 100,000 years or more. The upper limit is set when the separation of the two stars becomes comparable to the distance to other nearby stars. In this case, the external influences of the neighbourhood stars will eventually disrupt the very tenuous gravitational link between the components of the binary. Periodic passages through the plane of our galaxy (which happens every 30 million years or so) can also disrupt wide binaries due to the influence of giant molecular clouds. It is, of course, impossible to determine these periods even remotely well and even orbital determinations with periods of 1000 years are regarded as very provisional. For the widest systems, the separation of the two stars can reach 10,000 astronomical units (by comparison Pluto is about 30 AU from the Sun and the distance to a Centauri is 280,000 AU).
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