When it comes to stars, three may not be a crowd. That’s according to a new paper published online before print in Astronomy & Astrophysics, which suggests that almost a quarter of twin star systems might have another sibling nearby. Astronomers examined the light from nearly 14,000 eclipsing binary stars, fortuitous arrangements in which a stellar pair’s orbit is edge-on from our point of view. Telescopes on Earth can’t see the individual stars, but they do observe dips in light intensity as one goes behind the other. For lone binary stars, those dips occur at regular intervals. But in the presence of a third star, this timing speeds up and slows down as the pair orbits its mate and gets nearer and farther from Earth. Researchers found that 2% of the eclipsing binaries had this signature swing back and forth. However, in another 22%, the team found partial shifts potentially caused by a slower orbit around a companion. These unfinished oscillations were just as likely to swing faster as slower, ruling out the possibility that the change was due to the interaction of the twin stars. If correct, this finding could modify our understanding of stellar formation, especially because scientists now believe binary stars are even more common than single-star systems. It also makes the skies of some exoplanets more exotic, as in the artist’s illustration of a planet in the three-star system Gliese 667 shown above.