Multi-Star Systems Harboring Planets With Very Strange Orbits

ALMA and SPHERE view of GW Orionis


Unlike our remarkably flat Solar System, with its planets all orbiting in the same plane, the alien star-system GW Orionis, located just 1,200 light-years away in the constellation of Orion, has three stars and a deformed, shattered and warped disc of tilted rings surrounding them. “Since more than half of stars in the sky are born with one or more companions, says astronomer Alexander Kreplin of the University of Exeter about pioneering new research that has revealed the first direct evidence that a three-star system can tear apart their planet-forming disc, “this raises an exciting prospect: there could be an unknown population of exoplanets that orbit their stars on very inclined and distant orbits.”

“Any planets formed within the misaligned ring will orbit the star on highly oblique orbits and we predict that many planets on oblique, wide-separation orbits will be discovered in future planet imaging surveys,” Kreplin added.

Three-Star System of GW Orionis

To reach these conclusions, a team from the Universities of Exeter and Leicester observed stellar system GW Orionis for over 11 years and mapped the orbit of the stars with unprecedented precision. “We found that the three stars do not orbit in the same plane, but their orbits are misaligned with respect to each other and with respect to the disc,” said team member Alison Young.

An international team of experts, led by the astronomers at the University of Exeter, identified GW Orionis where planet formation might take place in inclined dust and gas rings within a warped circumstellar disc around multiple stars based on observations with the European Southern Observatory’s Very Large Telescope (VLT), Georgia State University’s Center for High-Angular Resolution Astronomy telescope array (CHARA), and the Atacama Large Millimeter/submillimeter Array (ALMA).

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Planets with Stunning Views

A view from a potential planet around this system will give the observer a stunning view of a tilted, multiple stellar constellation – similar to Star Wars’ Tatooine, reports the University of Exter team.

The research is the first output of a large program on young stellar system that uses a pioneering infrared imager, called MIRC-X, designed to give new insights into how star and planet formation is taking place within the rotating, circumstellar discs of dense dust and gas surrounding young stars. The imager combines the light from all six telescopes of the CHARA telescope array.


ALMA and SPHERE view of GW Orionis


“We’re really excited that our new MIRC-X imager has provided the sharpest view yet of this intriguing system and revealed the gravitational dance of the three stars in the system. Normally, planets form around a flat disc of swirling dust and gas- yet our images reveal an extreme case where the disc is not flat at all, but is warped and has a misaligned ring that has broken away from the disk,” said Stefan Kraus, professor of astrophysics at the University of Exeter, who led the research published in Science.

“Instead it is warped and has a misaligned ring that has broken away from the disc. The misaligned ring is located in the inner part of the disc, close to the three stars. The effect is that the view of a potential planet within this ring looks remarkably like that of Tatooine, of Star Wars fame.”

Inner Ring Contains 30 Earth Masses of Dust

The team observed the system with the SPHERE instrument on ESO’s VLT and with ALMA, and were able to image the inner ring and confirm its misalignment, revealing that this inner ring contains 30 Earth masses of dust, which could be enough to form planets. The team observed shadows that this ring casts on the rest of the disc. This helped them figure out the 3D shape of the rings and overall disc geometry.

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“We conducted simulations that show that the misalignment in the orbits of the three stars could cause the disc around them to break into distinct rings. This is what we see in the observations.”, said Matthew Bate, professor of theoretical astrophysics at Exeter, who carried out some of the computer simulations on the system. “The observed shape of the inner ring also matches predictions on how the disc would tear.”

The research was presented in the paper “A triple star system with a misaligned and warped circumstellar disk shaped by disk tearing” published in the journal, Science.

The Daily Galaxy, Sam Cabot via University of Exeter, Carnegie Institute for Science and Science

Image credit: ESO/L. Calçada, Exeter/Kraus et al.

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