In the Orion constellation, approximately 1,300 light-years from Earth, the young triple star system GW Orionis continues to baffle astronomers. Several rings of dust and gas — the future building blocks for planets — orbit its three stars. These rings have long been known for their unusual characteristic: they are tilted at different angles and do not lie in a single plane.
For a long time, the gravitational influence of the stars themselves was believed to be the cause. However, new observations are now revealing a different, more dynamic picture.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have discovered a colossal gas stream, or "striper," measuring approximately one trillion miles, or 0.2 light-years, in length. This flow slowly but steadily feeds the system, delivering material from the surrounding molecular cloud directly to the outer disk.
Researchers, led by Maria Galloway-Sprietsma from the University of Florida, meticulously studied the gas's movement by analyzing molecular carbon monoxide lines. They found that the striper's trajectory aligns with the orientation of the outer dust ring but significantly deviates from the position of the inner ring. Scientists believe this discrepancy precisely explains the observed tilts.
“When we modeled how the flow impacts the disk, the angle of its strike turned out to be closely related to the outer ring,” Galloway-Sprietsma noted. Calculations show that the striper's current angular momentum is less than that of the disk.
This suggests that we are observing a later stage of the process: previously, the flow likely carried more momentum and managed to "warp" the outer regions. Meanwhile, the inner rings remain largely unaffected.
ALMA proved to be the ideal instrument for this research. Its high resolution and sensitivity allowed scientists not only to visually detect the striper on a large scale but also to track its kinematics.
Archival data from dust ring observations were complemented by new measurements utilizing all of the telescope's arrays — the 12-meter, 7-meter, and Total Power. As a result, the striper could be linked to the surrounding star-forming region. The system, it appears, continues to accrete material from its parent cloud through a mechanism similar to Bondi-Hoyle accretion.
This scenario starkly contrasts with conventional textbook diagrams, which depict planets forming in serene, flat disks. Reality, it turns out, is far more turbulent: external gas flows can reshape disks even in their later stages of life, potentially giving future planets tilted or even retrograde orbits. GW Orionis now serves as a natural laboratory for studying such processes.
Researchers plan to search for similar streamers in other young systems to determine how widespread this mechanism is. For GW Orionis itself, upcoming ALMA observations will focus on molecules that indicate shock waves at the point where the flow collides with the disk. This will provide a more precise understanding of how the incoming gas alters the chemical composition and dynamics of the material from which planets might one day form.
