Astronomers have mapped themagnetic field inside DR21, one of the most active star-forming regions near the Sun, and found that it plays a direct role in feeding gas into the cloud’s dense core. The observations show that magnetic fields act as pathways, guiding material toward the regions where massive stars are taking shape.
The study, published inThe Astrophysical Journal, offers the most detailed look yet at the magnetic structure of DR21. It also helps explain how huge amounts of gas are funneled into the cloud’s central ridge, a key step in the star-formation process.
DR21, located within the Cygnus X complex, is an ideal place to investigate that question. The region contains a dense structure known as the DR21 Main Ridge, a filament about 13 light-years long that holds roughly 20,000 times the mass of the Sun in extremely cold molecular gas. Around it lies a network of smaller filaments that appear to be connected to the ridge.
Magnetic Fields Feed the Cloud’s Core
The new observations suggest that the magnetic field is doing much more than simply threading through the cloud. It is actively directing gas toward the Main Ridge. Lead author Thushara Pillai of MIT Haystack Observatory compared the process to a railway system.
“The magnetic field acts like a set of railroad tracks,” Pillai said. “Gas flows along the tracks toward the central ridge, building it up over time. Across the tracks, the field resists motion. So the field doesn’t stop star formation—it channels it.”
Researchers were able to follow the magnetic field from the dense ridge into the surrounding sub-filaments, something previous observations could not achieve. Those smaller filaments had already been suspected of supplying material to the ridge. The new map shows how the magnetic field links the structures together and provides routes for gas to flow inward.
A Massive Structure Built By Steady Inflows
The observations come from SIMPLIFI (Study of Interstellar Magnetic Polarization: a Legacy Investigation of Filaments), a SOFIA Legacy Program involving scientists from more than a dozen institutions around the world. The research compared the orientation of the magnetic field with the pull of gravity and the shape of the gas structures. They found that gravity and magnetic fields are closely aligned throughout the cloud.
This alignment is a classic sign of magnetically guided accretion, where gas moves inward along magnetic field lines toward the cloud’s center of mass. The findings indicate that the process is taking place across DR21 on a large scale. The team estimates that the surrounding sub-filaments are feeding enough material into the Main Ridge to build its massive structure in roughly one million years.
The work also required extensive processing of polarization data collected by SOFIA. As Jens Kauffmann, who led the data reduction effort, said:
“Working with SOFIA’s polarization data was challenging,” Kauffmann said. “We had to characterize the data reduction systematics from scratch. But the result was worth it: a homogeneous map of the magnetic field across an entire star-forming complex, at a level of detail that no other facility could provide.”
An Simple Explanation to an Old Mystery
The study also clears up an issue that had puzzled astronomers for years. Earlier observations detected gas moving toward the Main Ridge, but the measured speeds seemed lower than gravity alone would predict. The new analysis points to the orientation of the cloud as the reason.
Researchers found that the magnetic field and the gas flowing along it are positioned almost entirely in the plane of the sky. From Earth’s perspective, that means much of the motion occurs sideways rather than directly toward or away from us.
As a result, only a small fraction of the gas’s true velocity appears in observations. It was never moving unusually slowly; astronomers were simply seeing only part of the picture. The data were collected by SOFIA(Stratospheric Observatory for Infrared Astronomy), a modified Boeing 747SP equipped with a 2.7-meter telescope. The observatory was retired in September 2022 after 12 years of operations.
“To really understand how magnetic fields shape star formation across the galaxy, we need to go further—to fainter emission, larger areas of sky, and clouds at every stage of evolution.” Pillai added, “That requires a space-based far-infrared mission with polarization capability. We don’t have one. Building one should be a priority for the next decade of astrophysics.”