InfiniteZero shares a report from Phys.Org: Did our sun have a twin when it was born 4.5 billion years ago? Almost certainly yes -- though not an identical twin. And so did every other sun-like star in the universe, according to a new analysis by a theoretical physicist from UC Berkeley and a radio astronomer from the Smithsonian Astrophysical Observatory at Harvard University. The new assertion is based on a radio survey of a giant molecular cloud filled with recently formed stars in the constellation Perseus, and a mathematical model that can explain the Perseus observations only if all sunlike stars are born with a companion. "We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud, and the only model that could reproduce the data was one in which all stars form initially as wide (more than 500 astronomical units) binaries," said co-author Steven Stahler, a UC Berkeley research astronomer. "These systems then either shrink or break apart within a million years." The study has been published in April on the arXiv server.