A Rare Planet Might Be Hiding in This Oddly Shaped, Triple-Star System

Two new studies explain why GW Orionis, a rare triple-star system 1,300 light years away, looks so misshapen

Left, a small bright spot surrounded by three rings of orange dust and cloud, including an inner ring that juts our nearly perpindicular to the others; right, a bright orange swirl of gases and dust
Left: an artist's rendering of the GW Orionis system depicts its misaligned rings of dust and gas. Right: a view of GW Orionis European Southern Observatory

Just 1,300 light years away from Earth, three young stars are locked in a rare gravitational dance. Two stars are orbitting one another, while a third star zooms around the pair at a distance of hundreds of millions of miles away.

This unusual triple-star system is known to scientists as GW Orionis (GW Ori), and it’s one of the most oddly shaped interstellar arrangements that astronomers have witnessed, reports Brandon Specktor for Live Science. (For comparison, in our own solar system, planets orbit a lone star: our sun.) A large cloud of gases and dust, leftover from the sun’s birth, swirls around the star in a flat plane, or what’s known as the circumstellar disc, reports Ashley Strickland for CNN.

Protoplanetary discs are particularly interesting to astronomers because they play a role in the “birth” of new planets. For young stars, like those in GW Ori, scientists theorize that material from these discs can coalesce and form into planets, as Lisa Grossman reported for Science News in May.

In GW Ori, however, it seems that the star systems’ disc has “ripped.” Now, in two studies, one published in The Astrophysical Journal Letters in May and another in Science this week, researchers reveal new information about the wonky structure of this star system’s disc—and its possible origins.

In 2017, a team led by Jiaqing Bi and Nienke van der Marel with the University of Victoria in Canada used the Atacama Large Millimeter Array (ALMA) telescope in Chile to get a closer look at GW Ori. They found that the system’s planet-forming disc actually consisted of three rings of dust and gases nestled inside one another, per an ALMA statement.

None of these three rings are aligned with the orbit of the stars, the researchers announced in their Astrophysical Journal Letters study. What’s more, the inner ring is completely misaligned with the other rings, jutting out at a sharp angle, per Live Science.

In a study published this week in Science, lead researcher Stefan Kraus with the University of Exeter and his team studied GW Ori for 11 years. Using computer models and their observed data, the researchers were able to show that the gravitational pull of the three stars in different planes is enough to warp and “tear” the protoplanetary disk that surrounds the system.

This finding is the first time that researchers have been able to provide direct evidence for this dynamic, known as the theoretical “disc-tearing effect,” even though they’ve been predicting it for years, according to a University of Exeter statement.

“There have been a number of theoretical studies on disk-tearing effects, but this is the first direct evidence of effect occurring in a planet-forming disk,” study co-author Alison Young tells Space.com in an email. “This demonstrates that it is possible for such disks to be warped and broken and raises the possibility that planets could form on highly inclined orbits around multiple star systems.”

However, both teams of researchers indicate that the disc-tearing effect doesn’t fully explain the star system’s topsy-turvy shape. Bi and van der Marel argue in their paper that another interfering presence might be causing the rupture: a newly birthed planet. “We think that the presence of a planet between these rings is needed to explain why the disc tore apart,” notes Bi in an ESO statement.

Adds co-author Nienke van der Marel in the ALMA statement, “Our simulations show that the gravitational pull from the triple stars alone cannot explain the observed large misalignment. We think that the presence of a planet between these rings is needed to explain why the disk was torn apart.”

Astronomers have not yet detected a planet in this system, and they would need to conduct further research to determine if a newly birthed planet is contributing to GW Ori’s disk rupture, per Space.com. However, the necessary ingredients for a planet are in place: Kraus and his team found that the star system’s inner ring contains enough dust to create 30 Earth-sized planets, per the ESO statement.

If a planet is discovered, it would likely be located at the breaking point between the inner and outer rings of the protoplanetary disk, reports Live Science. It would also be the first planet ever discovered to orbit all three of its suns at once.

The view from this planet would also resemble the sunset on the fictional planet Tatooine of Star Wars fame, Kraus notes in the Exeter statement. Except unlike Luke Skywalker’s desert home, which bakes in the heat of two suns, this one would orbit three.

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