Around a star that is still forming, astronomers have observed a magnetic field coiling around a powerful stream of gas. This shape, long predicted by models, could explain how some young stars expel matter in narrow jets rather than in all directions.
The object studied, NGC 1333 IRAS 4A, is located about 956 light-years from Earth. It contains two protostars, meaning two very young stars that continue to grow thanks to the gas and dust surrounding them.
NGC 1333 - The Perseus molecular cloud, a site of star formation
Some of this matter falls toward the stars. The rest, by contrast, moves back out into space in the form of jets. Researchers have long sought to understand how these jets remain so narrow over great distances.
The magnetic field appears to provide part of the answer. As the matter rotates around the young star, it drags the field lines along with it. These eventually coil around the jet, like a thread around a tube.
This coiled shape can then keep the gas close to the jet’s axis. In other words, the magnetic field helps the expelled matter move in a precise direction instead of gradually dispersing to the sides.
To observe this invisible structure, the team used the ALMA radio telescope array in Chile. The light emitted by the gas makes it possible to indirectly determine the orientation of the magnetic field. The measurements indicate that it does indeed surround the stream of matter and follow its rotational motion.
The observation therefore provides direct support for a scenario used to explain the birth of stellar jets. Until now, this shape of the magnetic field had been expected based on models. Researchers now have an observation that will allow them to study more precisely how magnetism guides matter around stars that are still forming.