ALMA Observes Interplay between Magnetic Force and Gravity in Massive Star Formation

The magnetic field is part of one of the four fundamental forces in nature. It plays a vital role in everyday life, from producing electricity in hydroelectric power plants to diagnosing diseases in medicine. Historically, the Earth's magnetic field served as a compass for travelers before modern technology was available. Crucially for life, the Earth's magnetic field acts as a shield protecting us from charged particles emanating from the Sun, which are accelerated by the Sun's magnetic field. Removing this shield would very likely extinguish life on Earth. So it may not be a surprise that magnetic fields also play an outstanding role far away from us, outside the solar system.

The Sun was born in a cloud of dust and gas about 5 billion years ago, and magnetic fields may have controlled its birth. Indeed, scientists still debate how magnetic fields affect the process of star formation. Among all of the stars, the formation of the most massive ones is still shrouded in uncertainty. For years, scientists believed that the magnetic field plays an essential role in the high-mass star formation process. But they only had a limited number of observational evidence to prove or disprove this theory.

A team led by Patricio Sanhueza of the National Astronomical Observatory of Japan used ALMA to tackle this long-standing problem. They observed a source called IRAS 18089-1732, a high-mass star-forming region 7600 light-years away, finding a well-organized magnetic field that resembles a spiral “whirlpool.” Contrary to their predictions, however, the magnetic field appears overwhelmed by another of the four fundamental forces in nature, gravity.

“In these extreme environments, gravity can shape the gas morphology and dominate the energy budget,” says Sanhueza. They further discovered that the magnetic field lines are twisted from the immense gravitational infall of gas.

The minor contribution of the magnetic field has caught them by surprise since they have previously found evidence of strong magnetic fields in a similar star-forming environment. This ALMA discovery reveals the diversity in which high-mass stars form, concluding, somewhat unexpectedly, that high-mass stars can be born in either strongly or weakly magnetized environments, “feeling” the interplay between different forces as we experience here on Earth.


thumbnail (2)

Magnetic field in the massive star-forming region IRAS 18089-1732 revealed by ALMA. The colors represent the intensity of the radio waves, and the lines depict the distribution of the magnetic field lines revealed by ALMA’s polarization observations.
Credit: ALMA (ESO/NAOJ/NRAO), Sanhueza et al.


These observation results were presented as Patricio Sanhueza et al. “Gravity-driven Magnetic Field at 1000 au Scales in High-mass Star Formation” in the Astrophysical Journal Letters on June 30, 2021.