Researchers believe they’ve discovered a planet orbiting three stars at the same time

TORONTO —
Researchers believe they may have discovered the very first instance of a planet orbiting three stars at once, although they still haven’t seen it yet.

Around 1,300 light-years away from Earth, there is a star system with three stars gravitationally bound to each other. According to a new study published in the Monthly Notices of the Royal Astronomical Society, some abnormalities in the dust rings around the stars suggest that there are hidden planets orbiting these three stars.

Earth’s solar system consists of planets orbiting a single, central star, but this is actually more unusual than multi-star systems. Around half of all star systems feature two stars — called a “binary pair” — and around one in five star systems feature three or more stars.

Until now, scientists have yet to discover a planet in a circumtriple orbit around three stars before.

“It’s really exciting because it makes the theory of planet formation really robust,” Jeremy Smallwood, lead author of the paper, said in a press release. “It could mean that planet formation is much more active than we thought, which is pretty cool.”

GW Orionis, or GW Ori is the name of the triple-star system that researchers looked at in this new study, using observations from the Atacama Large Millimeter/submillimeter Array (ALMA) telescope.

While the telescope didn’t capture direct evidence of a planet, researchers believe that the unusual physical characteristics of the star system could only be explained by the presence of one or more massive hidden planets in orbit around all three stars.

In GW Ori, the first two stars are the same distance away from each other as the Earth is to the Sun, known as an astronomical unit (au). The third star is around eight au away from the first two.

The interesting thing about the star system is the discs of dust and gas swirling around the stars, containing the building blocks for planet creation. Researchers observed three dust rings that were misaligned with each other, and that there was also a large break or gap in the dust rings at around 100 au.

What could’ve caused this? Researchers set out to discover the cause.

One theory as to what formed these dust rings was that the torque from the three stars could be separating the disc of gas around the stars into these distinct layers. When simulated, the pressure of these stars could warp, but could not break the disc in the way researchers were observing in GW Ori.

Researchers compared the triple-star system to a binary star system and found they could model the circumtriple disc as a circumbinary disc, which allowed them to run more simulations to test what could break the disc.

Researchers then ran through what would happen in this star system if a planet was orbiting the three stars.

“The results of the simulations […] shows that if a planet forms in a misaligned disc and is massive enough to carve a gap, it can lead to an effectively broken disc,” the study stated.

They also found that if a planet formed in a misaligned disc, it would grow in size every time its orbit brought it back in sync with the disc again, and that it could carve multiple gaps in the disc.

Researchers estimate that the most likely planet to create the structures we see around this star system would be one or more large, Jupiter-style gas giants, although they add that under certain scenarios, a low-mass planet would also be capable of creating a gap in the dust rings if it was orbiting more consistently along the dust ring.

Despite the evidence pointing towards the first planet — or planets — to be found orbiting three stars at once, it may be hard to prove it definitively.

“If misaligned planets are present around the hierarchical triple-star system, they would be difficult to detect,” the study stated.

One of the most common methods to detect planets in distant star systems is the transit method, in which we record the level of light coming from a star and can detect a planet passing in front of the planet by the dimming of the light that occurs when the planet is in front of the star. It’s easier to detect planets that orbit on a consistent plane, which may not be the case with GW Ori’s potential planets.

Still, researchers will be on the lookout for more data using ALMA, hoping to find direct evidence of the first case of a circumtriple orbit.