Astronomers may have found the very first exoplanet orbiting three stars

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(ALMA (ESO / NAOJ / NRAO), ESO / Exeter / Kraus et al.)
Since last year, astronomers have taken a look at a fascinating triple star system about 1,300 light years away. The system, known as GW Orionis, is surrounded by cloudy dust, indicating that it is still very young. Scientists have struggled to explain the twisting and contortion of the dust rings. According to Bad Astronomy, a new analysis may have found a cause: a one-of-a-kind exoplanet that orbits all three stars in this solar system.

GW Orionis is what is called a hierarchical trinary. It’s the same cluster as the Centauri Solar System next door with two stars in close orbit, plus a companion orbiting at a greater distance. In GW Orionis, the two closest stars are 180 million kilometers apart, slightly more than the distance between the Earth and the sun. Meanwhile, the outer limb is 1.2 billion kilometers away, which is roughly the distance between the sun and Saturn.

These stars are surrounded by a disk of dust and gas, which is common for young solar systems. Eventually, some of this material could melt into planets, but most of it will be swept away by increasingly powerful solar winds. Around GW Orionis, dust fell in a series of severely deformed rings. You can see a simulation of the rings below. Above, the image on the left is an artist’s impression and the image on the right is observation data from the ALMA radio telescope array.

The new research, led by astronomer Jeremy Smallwood, used orbital and particle simulations to somehow search for the outer star of the trinarian that could disrupt the rings. Despite their best efforts, the researchers couldn’t find a way for the star itself to break the rings. So they tried something new and added a planet to the system. There are known exoplanets in the trinary systems – Centauri has a few, in fact. However, they’re all orbiting one or two stars in the cluster. We have never found a planet orbiting three stars because such a system is inherently unstable. And yet, adding a planet in this setup seems to work.

According to the study, if the protoplanetary disk is thick (10 times wider than it is thick), the exoplanet cannot affect the rings as seen from Earth. However, if it were 20 times wider than it was thick, the planet can widen a gap very similar to what we are seeing. Some features of the GW Orionis system are still unexplained, such as the arched structures mirrored in the middle. Much more analysis will be needed to see what impact, if any, the proposed planet might have on these.

This exoplanet is not yet confirmed, but it could be a first for astronomy. About half of all stars are in binary systems, and maybe twenty percent are in trinaries. Finding out that exoplanets can orbit a trinarian could mean that there are many more worlds. GW Orionis is still young, however. It is possible that planets like this often form, but then be ejected to become rogue planets, and we suspect there are a lot of them.

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