Magnetic fields are thought to play a critical role in how stars form and accumulate mass. Now scientists have detected a magnetic field around a young star and are learning surprising details about the field’s form and structure.
All stars are formed in cold, dense cores of molecular clouds. During the collapse of a core into a new young star (called a protostar), a circumstellar disk is created.
This disk will eventually form planets and become a system like our solar system. At the early stages of star formation, this circumstellar disk is responsible for allowing mass to accrete onto the protostar. This accretion is thought to be regulated by magnetic fields, but different theoretical models suggest different magnetic field morphologies.
The magnetic fields in the disk may be toroidal (i.e., circular fields within the disk) or poloidal (i.e., fields emanating from the poles of the protostar). Unfortunately, numerous observations in search of the magnetic field morphology have found no detection.
Ian Stephens, a postdoctoral associate for Boston University’s Institute for Astrophysical Research, along with a collaboration of people at the University of Illinois and throughout the world, used Caltech’s Combined Array for Research in Millimeter-wave Astronomy (CARMA) telescope in California to search the disk of the T Tauri star HL Tau—a protostar located 450 light-years away that started its formation process approximately 1 million years ago.
From Earth, HL Tau has the brightest T Tauri star disk at millimeter wavelengths. These CARMA observations found the first detection of the magnetic field morphology in a T Tauri star disk.
According to the study, “the unexpected morphology suggests that the magnetic field’s role during the accretion of a T Tauri star is more complex than the current theoretical understanding,” and that magnetic fields are important in forming a planetary system like our own.
While the magnetic field morphology appears significantly more toroidal than poloidal, neither morphology is a good fit. This is at odds with current theoretical expectations and suggests that the role of magnetic fields is more complicated than our current understanding.
Future observations with the Atacama Large Millimeter Array in Chile are forthcoming for HL Tau and other disks. These observations can study the magnetic field morphology in greater detail, which will provide better insight of the role of magnetic fields in circumstellar disks.
For more information on Stephens’ findings, read the full study in Nature.
Source: Boston University