Astronomers have discovered an enormous stream of gas flowing toward a young system of three stars, potentially explaining why its planet-forming disks are strangely tilted.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), researchers observed a gas streamer stretching about one trillion miles, or 0.2 light-years, toward the young triple-star system GW Orionis.
The findings, published in The Astronomical Journal, offer new clues about how incoming material can reshape the environments where planets are born.
GW Orionis is located about 1,300 light-years from Earth in the constellation Orion. The system contains three young stars surrounded by several rings of gas and dust—the raw materials from which planets can eventually form.
What makes GW Orionis especially unusual is that its rings do not all lie neatly in the same flat plane. Instead, the inner, middle and outer rings are tilted at different angles.
Researchers led by Maria Galloway-Sprietsma, a Ph.D. candidate at the University of Florida, wanted to determine whether the huge gas streamer could help explain this unusual arrangement.
The team measured how the gas is moving toward the system and compared its direction of motion with the orientations of the planet-forming rings. They found that the streamer’s path closely matches the angle of the outer dust ring but is strongly misaligned with the inner ring.
This connection suggests that gas falling into the system may have helped push the outer disk into its unusual tilted position.
The discovery challenges the traditional picture of planet formation. Young planetary systems are often shown as relatively calm, flat disks of gas and dust surrounding their stars. Planets then gradually form within these orderly disks.
But real planet-forming environments may be much messier.
Large streams of gas from the surrounding material can continue feeding young star systems and may arrive from unexpected directions. If enough material falls onto a disk at an angle, it could change the disk’s orientation. Planets forming there could then end up traveling on highly tilted orbits—or potentially even orbiting in a direction opposite to the rotation of their host star.
ALMA allowed the researchers to examine both the enormous size of the streamer and the movement of gas within it. They studied signals from carbon monoxide molecules to calculate the streamer’s angular momentum, a measure related to how matter rotates and moves around a system.
The researchers found that the streamer currently has much less angular momentum than GW Orionis’ disk. This suggests the system may be witnessing the final stages of a much larger period of gas infall.
In the past, the streamer may have carried considerably more material and angular momentum, giving it enough influence to tilt the outer disk. Today, however, it probably does not have enough power to change the disk much further.
Astronomers now want to study other young star systems to determine how common these enormous gas streamers are.
Future observations of GW Orionis will also search for molecules that can reveal where the incoming gas crashes into the disk.
Understanding these dramatic interactions could ultimately help explain why some planets elsewhere in the galaxy follow surprisingly tilted and unusual orbits.
