Double Take

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Science  21 Apr 2006:
Vol. 312, Issue 5772, pp. 339
DOI: 10.1126/science.312.5772.339b

Most stars exist as binaries, in which two stars orbit one another about their common center of mass. Statistically, individual stars can span a wide range of masses, and there are many more light stars than heavy ones, so if binaries assemble at random, the relative masses of their constituents should generally differ significantly. Moreover, the more massive star in the pair should evolve and die more quickly than its companion.

Pinsonneault and Stanek suggest that a surprisingly high proportion of binaries are twins, with both stars of about the same mass and age. In a spectroscopic sample of the nearby Small Magellanic Cloud galaxy, about half of the well-separated binary pairs are twins, far more than chance would predict. Other literature reports are consistent with twins constituting at least a quarter of all binaries. Because the twin stars are identical, they must both have formed at the same time and evolved at the same rate. This preponderance of twins may impinge upon a range of astrophysical questions related to the interactions, mergers, and deaths of binary stars, including the progenitors of (Type Ia) supernovas and gamma-ray bursts. — JB

Astrophys. J. 639, L67 (2006).

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