One Sun is plenty for our solar system, but some planets have been found orbiting two stars at once. Now the ante has been upped again, with evidence emerging of a planet orbiting three stars at once.
About 1,300 light-years away from Earth in the constellation of Orion lies a star system known as GW Orionis (or just GW Ori), which contains three relatively young stars locked in orbit around each other. These stars are surrounded by a large protoplanetary disc – wide rings of dust from which planets can coalesce. And new observations suggest that perhaps there’s already one on the scene.
Previous observations found that the disc is separated into three rings, with a particularly large gap about 100 Astronomical Units (AU) from the stars. The rings also seemed to be misaligned, with the innermost one warped at a weird angle to the others.
There were two leading hypotheses about what could be creating this structure. Either the gravitational influence of the three stars was breaking the disc apart – or a massive planet was forming and carving the gap in the disc. So to probe deeper, Astronomers from the University of Nevada Las Vegas created a comprehensive model of the system.
The results showed that the torque from the stars shouldn’t have been enough to break the disc like this. However, a Jupiter-sized gas giant planet (or several of them) fit the bill, emerging as the most likely culprit. These worlds are usually the first to form out of protoplanetary discs, followed by the smaller rocky planets like Earth.
The model suggests that after the planet (or planets) scooped out a chunk of the disc, it split into the three rings which then move at different rates, leading them to become misaligned over time.
Right: A SPHERE image of the system, with the shadow of the inner ring cast on the rest of the disc
If there is a planet in the GW Ori system, it would be the first ever found to be orbiting three stars at once. Planets have previously been discovered orbiting two stars, while others have been discovered orbiting a single star that also happens to have two companions. But this would be the first in a so-called “circumtrinary orbit.”
“It’s really exciting because it makes the theory of planet formation really robust,” says Jeremy Smallwood, lead author of the study. “It could mean that planet formation is much more active than we thought, which is pretty cool.”
The planet itself hasn’t actually been spotted yet, but the team says that future observations by ALMA could help find it and settle the debate.
The research was published in the journal Monthly Notices of the Royal Astronomical Society.
Source: University of Nevada Las Vegas
