What is the largest distance between stars in a binary star system?
Off hand, I don’t know the answer to this. It would depend on where the star is located. If it is in a dense star cluster where the mean stellar separations are a light year or less, then this distance would have to be, perhaps, 10 billion miles ( 100 AU) or less otherwise the stars would be so loosely bound together that a passing star could disrupt the binary system. In the vicinity of the Sun, I think the largest separations between stars in identifiable binary systems runs to something like 100 billion miles or 1000 Astronomical Units; some 25 times the distance to Pluto. In terms of observing binary stars with separations more than a few billion miles, they move so little in their orbits in a few decades that they can be easily overlooked. I believe many of the most common binary stars have orbits less than 50 years. There are about 70,000 binary stars known with several such as Castor with periods of 420 years, and 61 Cygni with a period of 720 years. The ones with the longest pe
