Astronomers have identified 27 new possible planets orbiting pairs of stars, similar to the fictional desert world Tatooine from Star Wars.

So far, only around 18 confirmed circumbinary planets, those that circle two stars, have been found, compared with more than 6,000 planets discovered orbiting single stars like Earth does around the Sun.

In a timely publication for 4 May, widely known as Star Wars Day, researchers reported nearly 30 new candidate worlds located between about 650 and 18,000 light-years from Earth.

“There are many things in astronomy that aren’t very tangible,” said Associate Prof Ben Montet of the University of New South Wales (UNSW), the study’s senior author. But thanks to the famous Tatooine sunset scene in the first Star Wars film, “everyone has a picture of what a circumbinary planet looks like and what would it mean to stand on a planet with two suns”.

More than half of all stars in the universe are thought to exist in binary or multi-star systems.
Previously, scientists detected circumbinary planets using the transit method.

As Montet explained, when a planet passes in front of a star, “it casts a shadow on the star’s surface, we see a dip in brightness of the star … and we can infer there’s something going around it.”

However, this method only works when a planet and its star system are perfectly aligned with Earth’s line of sight.

“We’re missing lots of systems, potentially,” Montet said.

“Planets are hard to find. It’s like trying to see a candle right next to a big street light.”

Instead, the researchers used a technique called “apsidal precession,” which looks for a subtle wobble in binary stars as they orbit one another and periodically eclipse each other.

“If we monitor the exact timing of these eclipses … that can tell us that there’s something else going on in the system,” said Margo Thornton, the study’s lead author and a PhD candidate at UNSW.

After ruling out other influences such as the stars’ rotation and mutual gravitational effects, the researchers pinpointed 36 systems out of 1,590 whose motion could only be explained by the presence of a third object.

For “27 of those objects, it is possible that they are planet mass”, Thornton said. More research into their spectra – the light they emit – was needed to formally confirm them as circumbinary planets, she said.

Further analysis of their spectra—the light they emit, will be required before the candidates can be formally confirmed as circumbinary planets, she said.

She added, “It’s just a matter of: what is the mass of it? Is it a planet? Is it a brown dwarf? Is it a star?”