A rare planet-forming disk around a young triple star system in the constellation Orion has been thrown off balance by an enormous “river” of gas stretching more than 1.2 trillion miles (1.6 trillion kilometers) in length.
The discovery, made using radio wavelengths captured by the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope in Chile, may explain why astronomers keep finding exoplanet systems whose orbits tilt sharply away from their stars’ rotational axes.
The Rare GW Orionis System
The GW Orionis system consists of three protostars, meaning they are still forming and contracting and haven’t yet begun hydrogen fusion in their cores. The stars sit roughly 1,300 light-years away, inside the Lambda Orionis star-forming ring in the Orion constellation. Finding a single gas-and-dust disk that surrounds all three stars and shapes planets is already extremely rare, but a three-ring disk with misaligned orbits is even more unusual.
Maria Galloway-Sprietsma, a doctoral student at the University of Florida who led the research, said previous studies of GW Orionis had already revealed that the system’s inner, middle, and outer rings weren’t aligned, with each ring tilted at a different angle.
The Mechanism Behind the Tilt
The outer ring, one of the largest ever observed around a young star, shows the most pronounced misalignment. Researchers initially theorized that an unseen gas giant planet was disturbing the ring. Instead, the team uncovered a different explanation: a massive gas “streamer” flowing in from the surrounding molecular cloud is disrupting the outer ring. The exchange of angular momentum between the two distorts the ring and pushes it into a tilt.
The disk itself is made up of three rings, sitting at distances of 4.1, 17.4, and 31.6 billion miles from the system’s center. The gas flow responsible for the tilt was discovered through new ALMA observations that detected carbon monoxide molecules, since molecular hydrogen itself is invisible at radio wavelengths. The streamer’s length is striking, stretching about 0.2 light-years, or 1.2 trillion miles.
“When our team modeled the inflow of this streamer, we found that the angle at which it strikes the disk lines up closely with the outer ring,” Galloway-Sprietsma said.
An Explanation for Planets’ ‘Crooked’ Orbits
In our own solar system, every planet orbits the Sun in a narrow plane aligned with its equator. While most exoplanets follow a similar pattern, scientists have previously spotted planets with sharply tilted or even backward orbits. With the discovery of this streamer at GW Orionis, astronomers may have found the driving force behind these unusual planetary systems.
“If these streamers are common, then we can naturally explain why planets don’t necessarily end up in very orderly systems,” said research collaborator Bae, adding that their orbits could end up pointing in far more random directions. Still, the researchers stress that a systematic survey of many young stars is needed to determine how common these streamers actually are and how much influence they have in shaping planetary systems.
