<P> Binaries provide the best method for astronomers to determine the mass of a distant star . The gravitational pull between them causes them to orbit around their common center of mass . From the orbital pattern of a visual binary, or the time variation of the spectrum of a spectroscopic binary, the mass of its stars can be determined, for example with the binary mass function . In this way, the relation between a star's appearance (temperature and radius) and its mass can be found, which allows for the determination of the mass of non-binaries . </P> <P> Because a large proportion of stars exist in binary systems, binaries are particularly important to our understanding of the processes by which stars form . In particular, the period and masses of the binary tell us about the amount of angular momentum in the system . Because this is a conserved quantity in physics, binaries give us important clues about the conditions under which the stars were formed . </P> <P> In a simple binary case, r, the distance from the center of the first star to the center of mass or barycenter, is given by: </P> <Dl> <Dd> r 1 = a ⋅ m 2 m 1 + m 2 = a 1 + m 1 m 2 (\ displaystyle r_ (1) = a \ cdot (\ frac (m_ (2)) (m_ (1) + m_ (2))) = (\ frac (a) (1 + (\ frac (m_ (1)) (m_ (2)))))) </Dd> </Dl>

What are the three types of binary star systems