There is a reason the most recognizable planet orbiting two stars is the fictional desert world of Tatooine from Star Wars. So far, astronomers have only located 18 examples of circumbinary planets—a fraction of the over 6,000 exoplanets known to science. However, researchers at Australia’s University of New South Wales (UNSW) believe there’s a better way to spot potential dual-sun candidates. To prove it, they just offered up 27 possible circumbinary planets in time for May 4th, aka Star Wars Day.
“Most of our current knowledge on planets is biased, based on how we’ve looked for them,” Margo Thornton, a UNSW astronomer, said in a statement. “We’ve mostly found the easiest ones to detect.”
As Thornton and her colleagues explain in a study published today in the Monthly Notices of the Royal Astronomical Society, the secret weapon is a technique called apsidal precession. Typically used to only confirm binary stars, astronomers using apsidal precession observe the twin stellar bodies orbit and eclipse one another over extended lengths of time.
Thornton’s team theorized a way to expand apsidal precession’s original use. While these stellar eclipses typically occur on predictable schedules, there are cases featuring tiny variations. The team argues that if these differences can’t be explained by general relativity or other standard interactions, then they may point to the existence of a planet.
This strategy differs from the transit method, where asteronomers identify exoplanets by the mini-eclipse they cause while passing in front of a star. While a common approach, the transit method has major limitations. Planets are only discoverable if they cross between Earth and their own star, meaning irregular orbits or orbits outside the direct line of sight are easily missed.
“This new method could help us uncover a large population of hidden planets, especially those that don’t line up perfectly from our line of sight,” Thornton said. “It could help reveal what the true population of planets in our universe might look like.”
Her colleagues are already surprised by the number of possible dual-star candidates located using apsidal precession.
“I wasn’t expecting to find 27 already at this point from the pilot study,” said study coauthor Ben Montet. “Now we get to start the really fun project of figuring out which ones are real planets.”
These potential circumbinary bodies range in size from about the mass of Neptune to 10 times as large as Jupiter. The closest is roughly 650 light-years from Earth, while the furthest is an impressive 18,000 light-years away.
Astronomers will next begin closer examinations to weed out any circumbinary false alarms. When they do, they’ll be looking in virtually every direction.
“The candidates are scattered across both our southern and northern skies,” said Montet. “This means that any time of the year, no matter when you’re looking, at least one of these star systems is out there visible for you to look towards.”
