As beautiful as sunsets are on Earth, imagine a double sunset with stars of different colors, casting moving shadows of orange and red. For years the two of us wondered if paired, or “binary,” stars could support planets. Could worlds like the fictional Tatooine from Star Wars, where the sky is lit with the glow of two different suns, really exist?
Astronomers had reason to think such systems might exist, yet some theorists disagreed. The environment around a pair of stars, they argued, would be too chaotic for planets to form. Unlike a body circling a single star, a planet orbiting a pair of stars would have to contend with two gravitational fields. And because the stars themselves orbit each other, the strength of the gravitational forces would constantly change. Even if a planet could form in such a dynamic environment, its long-term stability would not be assured—the planet could wind up being ejected into deep space or crashing into one of the stars. Observations of binary star systems had shown some indirect evidence for these “circumbinary” planets, but direct evidence remained elusive.