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I know this is such a thing as a binary star where for example two stars rotate around a central point of gravity but to the naked eye are just a star. What I do not know is how common this is (approximately)?

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Point of clarification: "Double stars" refers to two stars that are visually very close together so they appear as one by the naked eye. But that doesn't necessarily mean they are binary stars. Do you have a preference? – Robert Cartaino May 29 '14 at 15:02
@RobertCartaino - i revised the question to be binary. cheers – esé May 29 '14 at 15:26
up vote 9 down vote accepted

This is a difficult question, It's been changing through the years and it's difficult to calculate accurately. Now it's know that this percentage changes depending on the star type and ranges from 50% for Sun like stars up to a 80% for type O stars.

Fonts: (2006) (2013)

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I think it's important to emphasize how approximate these numbers are. This question is frequently debated, and we simply don't have a good, solid answer. – Kyle Neary May 29 '14 at 19:25
Is this answer actually answering a different question: 'how many stars [in general/in the Milky Way] are binaries'? If the question is regarding visual stars ie naked eye objects then we can be much more definite... – Jeremy May 30 '14 at 20:57

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