"Our main result is that outside a small region near a binary star, [either rocky or gas-giant] planet formation can proceed in much the same was as around a single star," the authors wrote. "In our scenario, planets are as prevalent around binaries as around single stars."
The study has been submitted to the Astrophysical Journal for review, but the unreviewed paper is available on the scientific preprint website ArXiv.
With "Star Wars: Episode VII - The Force Awakens" due to take movie theaters by storm on Dec. 18, the reality of a home planet like Tatooine - birthplace of both Luke and Anakin Skywalker, meeting place of Obi Wan Kenobi and Han Solo and geography ruled by Jabba the Hutt - could be a bit surreal.
The title of the new study is "Planet Formation Around Binary Stars: Tatooine Made Easy." The study is bursting with mathematical formulas describing how binary stars can be orbited by planetesimals -- asteroid-size rocks that clump together to form planets.
"We took our sweet numerical time to show that the ride around a pair of stars can be just as smooth as around one," Bromley said, according to a press release from the University of Utah. "The 'made easy' part is really saying the same recipe that works around the Sun will work around Tatooine's host stars."
The study was funded by NASA's Outer Planets Program and was a "spinoff" of Bromley's and Kenyon's research into how dwarf planet Pluto and its major moon, Charon, act like a binary system, according to the press release.
"Planets form like dust bunnies under your bed, glomming together to make larger and larger objects," said Kenyon, according to the press release. "When planets form around a binary, the binary scrambles up the dust bunnies unless they are on just the right orbit."
"It's an oval with ripples," which are caused by the cyclic tugging of the two central stars, Bromley said, according to the press release. "For over a decade, astrophysicists believed that planets like Earth could not form around most binary stars, at least not close enough to support life. The problem is that planetesimals need to merge gently together to grow. Around a single star, planetesimals tend to follow circular paths - concentric rings that do not cross. If planetesimals do approach each other, they can merge together gently."
Typically, "their paths get mixed up by the to-and-fro pull of the binary stars," Bromley continued. "Their orbits can get so tangled that they cross each other's paths at high speeds, dooming them to destructive collisions, not growth."
The new data shows "planets, when they are small, will naturally seek these oval orbits and never start off on circular ones," Bromley said. "If the planetesimals are in an oval-shaped orbit instead of a circle, their orbits can be nested and they won't bash into each other. They can find orbits where planets can form."
Mathematically and with simple computer simulations, the researchers showed that that rocky, Earth-size planets can form around binary stars if they have the oval "most circular" orbit. The study suggests that planetesimals could survive without collisions for tens of thousands of years in concentric, oval-shaped orbits around binary stars.
"We are saying you can set the stage to make these things," Bromley said, according to the press release. "It is just as easy to make an Earth-like planet around a binary star as it is around a single star like our Sun. So we think that Tatooines may be common in the universe."