There may be planets orbiting the three stars in GW Orionis’ system

GW Orionis' protoplanetary dsk
An article published in the journal “Monthly Notices of the Royal Astronomical Society” reports a study on the triple system of GW Orionis, or simply GW Ori, which claims that there is at least one exoplanet, which would be the first known to orbit three stars. A team of researchers led by Jeremy Smallwood of the University of Nevada Las Vegas examined observations of the rings of GW Ori’s protoplanetary disk made with the ALMA radio telescope. The goal was to try to establish the cause of the presence of void within one of them and the conclusion is that one or more exoplanets have formed or are forming.

In 2020, the discovery of three rings in a misaligned disk in GW Ori’s triple system aroused the interest of astronomers. The protoplanetary disk had been known for quite some time but its particular structure was not. It’s the first known structure of its kind and is intriguing because the rings have enough masses to form giant planets. Exoplanets are known that orbit around a single star that is part of a triple system such as those existing in the Alpha/Proxima Centauri system but the possibility of having exoplanets orbiting three stars arouses much greater curiosity.

So far, no exoplanet has been detected directly or indirectly in GW Ori’s system but this could be due to limitations of the instruments used to observe it and to the still abundant dust in the protoplanetary disk. However, at a distance from the mass centers of GW Ori’s stars of about one hundred times that of the Earth from the Sun, there’s a void in one of the rings. Previous research is divided on the cause offering very different probabilities that it is due to at least one exoplanet or to gravitational interactions between the three stars. Jeremy Smallwood’s team tried to investigate the issue.

The examination of the observations of the GW Ori system conducted with the ALMA radio telescope (Image ALMA (ESO/NAOJ/NRAO), S. Kraus & J. Bi; NRAO/AUI/NSF, S. Dagnello. 2017: Bi et al. 2018 Kraus et al.) and a series of simulations of the dynamics within it indicate the possibility that a massive planet could create a void inside a ring of fine dust as its orbit moves in and out of the protoplanetary disk’s plane. There’s also the possibility that there’s more than one planet in that area.

These conclusions are still approximate and are based on mathematical calculations, so there’s still a need for verification. The different conclusions offered by the various studies on the GW Ori system show how difficult it is to obtain results with high probability starting from limited information.

New observations of the GW Ori system with the ALMA radio telescope are expected in the coming months. They will certainly offer new information, and Jeremy Smallwood’s team hopes they will also include evidence of the existence of at least one exoplanet. According to current models of planetary formation, gas giant planets are the first to form in a protoplanetary disk but can still be difficult to detect.

The team also intends to work on a more general project concerning the stability of circumtriple planets, that is, such as those that might exist in the GW Ori system, to try to understand how stable they can be. The distance from the stars that the planets in GW Ori would have should be enough to have a stable orbit. All that remains is to verify if they really exist!

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