Protoplanetary System with 3 Stars Has Been Spotted in the Orion Constellation

Pablo Tucker
September 5, 2020

An global 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).

"Our simulations show that the gravitational pull from the triple stars alone can not explain the observed large misalignment". The ALMA image (blue) shows the disk's ringed structure, with the innermost ring (part of which is visible as an oblong dot at the very center of the image) separated from the rest of the disk.

Using the European Southern Observatory's Very Large Telescope (ESO's VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA, ) a team of astronomers found the first direct evidence that stars can tear apart the planet-forming, or circumstellar, disc that surrounds them. Image credit: ALMA / ESO / NAOJ / NRAO / ESO / University of Exeter / Kraus et al. The GW Orionis (or GW Ori) solar system from the Orion constellation is the new attraction point for astronomers, as it's home to not one, but three stars. It consists of three rings, wrapped around three stars - and all three rings have different trends, which are incorrectly placed internally from the other two.

Luckily, although the misalignment was only discovered recently, GW Orionis has been monitored since 2008, and the third star in the system was discovered in 2011. The inner ring is also fully misaligned with the larger outer rings. By transporting material out of the disk plane, they say, the disk-tearing effect could provide a mechanism for forming planets on oblique or retrograde orbits. For comparison, Neptune is only about 30 AU from the Sun.

"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 disc", study lead and professor of astrophysics at the University of Exeter, Stefan Kraus, said in an ESO news release. "But the strange-poor stress in the disc is confirmed by a reversal pattern measured by the ALMA in the disc's gas". The biggest surprise was due to the images of the inner ring, confirming how misaligned it is.

The new finding is detailed in a study published Thursday in the journal Science.

ALMA inspection (left) and VLT (right). Orange rings are the (misaligned) rings seen by ALMA.

Alas, even if the hypothetical planet does exist, there will be no Skywalkers gazing wistfully out at the three-sunned horizon; according to the team's models, this world would have to sit roughly 46 AU from its host stars - considerably farther afield than Neptune sits from our sun (30 AU). Image credit: Kraus et al / NRAO / AUI / NSF. The team also mapped the orbits of the system's three stars over 11 years, covering one complete orbital period. The researchers discovered that the stars were misaligned, compared to each other as well as the disk, and that they did not orbit in the same plane.

"This proved crucial to understand how the stars shape the disk", said Professor John Monnier, an astronomer at the University of MI. From this, they developed a three-dimensional model and simulation of the system, which reproduces the eccentric inner ring and a strongly warped intermediate region of the disk. The simulation revealed that the stars had torn apart their disc themselves due to their conflicting gravitational pull, with each one pulling on the disc in a different direction.

Our simulations show that the gravitational pull from the triple stars alone can not explain the observed large misalignment [in the rings],We think that the presence of a planet ... has likely carved a dust gap and broken the disk [where the inner and outer rings meet].

The simulations by Bi and colleagues hint at another possible explanation for the large misalignment between the inner and middle dust rings. "We think that the presence of a planet between these rings is needed to explain why the disk was torn apart", study-co author of the earlier study, Nienke van der Marel of the University of Victoria, said in a news release from the National Radio Astronomy Observatory.

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