AN EXOPLANET ORBITING THREE STARS?
Astronomers may have found the first planet that orbits a trio of suns.
Some 1,300 light-years away in the constellation Orion the Hunter is the triple-star system GW Orionis. This trio of young stars is only about 1 million years old and still surrounded by a disk of dust and gas left over from their formation. This socalled protoplanetary disk is organized into three concentric rings, none of which are aligned with any of the orbits of the three stars. Additionally, the innermost ring is out of alignment with the outer two rings; it also tilts and wobbles as it orbits. And there’s a large gap between the inner and middle rings, indicating the material there has been cleared out.
A paper published Sept. 17 in Monthly Notices of the Royal Astronomical Society suggests the reason for that last oddity is a so-called circumtriple planet (or planets) forming within the disk, orbiting all three stars at once and clearing out material to form the gap.
MAKING SPACE
Gaps in protoplanetary disks often indicate where planets are forming within them. As a planet pulls in nearby gas and dust to grow, it clears out its surroundings. But in this case, researchers weren’t sure whether the disk’s behavior should be attributed to a fledgling planet or the three stars whirling in a complex dance at its center.
They found, based on 3D modeling, that the stars’ gravity can’t produce enough torque to create the observed gap. Instead, the researchers say, it is likely due to at least one Jupiter-sized planet forming there. If confirmed, it would be the first exoplanet found orbiting three stars. (Although planets have been found in nearly 30 triple systems to date, none of these other worlds orbit all three stars.)
The supposed planet orbits about
100 astronomical units (AU) from the center, where 1 AU is the average EarthSun distance. The stars themselves are much closer: Two orbit each other separated by just 1 AU, while the third orbits both of these some 8 AU from the system’s center.
Because this research only provides indirect evidence for the planet, the next step is actually spotting the strange world. Unfortunately, the authors conclude, that’s tricky in a system this complex. Still, more observations are coming down the pike, which may yet reveal a glimpse of a truly unique young world.