It is well known that the Sun undergoes an 11-year solar activity cycle, a phenomenon where the intensity of the Sun's magnetic field changes and its polarities reverse. Over the past 30 years, scientists have identified similar behavior in other Sun-like stars. However, no reversal of magnetic polarities has been observed for their cooler counterparts - the red dwarf stars.
Understanding Stellar Magnetic Fields
A stellar magnetic field refers to the magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, a form of energy transport that involves the physical movement of material.
These magnetic fields are similar in nature to the effect of the well-known dipolar magnets typically found in laboratories, but far more powerful and infinitely more complex. They are also an important component of the physical makeup of stars since they affect their interiors, atmospheres, and immediate surroundings.
Magnetic fields play an important role at many stages of star formation and evolution. They represent a key ingredient of stellar and planetary system formation processes. They are also responsible for the angular momentum loss in young stars and is the major energy source behind a broad range of dynamic phenomena which take place at the surface layers of the Sun and other stars. However, detecting and direct modeling of magnetic fields have always been challenging for astronomers.
Studying stellar surface magnetic fields offers relevant insights into the internal structure of stars, in addition to their significant role in stellar formation, evolution, and activity. For cool stars, observing changes in the configuration of magnetic fields offers useful feedback on the processes that operate in the stellar interior and constraints on stellar wind models.
Polar Reversal of AD Leonis
An international team of scientists has shown that the extremely active red dwarf AD Leonis may be having a reversal of its magnetic field. Led by Stefano Bellotti, the data were gathered using the NARVAL at the Bernard Lyot Telescope (BLT), and ESPaDOnS and SPIRou instruments at the Canada-France-Hawaii Telescope (CFHT).
AD Leonis is known for being a notoriously active red dwarf star which contains a magnetic field that is about 1,000 times stronger than that of the Sun. There is evidence of its activity cycles, but it is not yet known whether red dwarfs can exhibit magnetic cycles.
This red dwarf has been under monitoring since 2006 with the ESPaDOnS and NARVAL instruments, and since 2019 with SPIRou. The study shows that the magnetic field intensity does not only decrease continuously over this period, but the star's magnetic poles have also begun to flip. While the polarities were not reversed during the SPIRou observations, the results indicate the red dwarfs such as AD Leonis may also experience magnetic cycles like our Sun.
The result of the study offers a better insight on the magnetic field generation of stars that are colder than the Sun. Additionally, studying the magnetic field of red dwarfs is important in understanding the space environment in which rocky exoplanets orbit, since the red dwarfs have been the prime targets in detecting Earth-like planets.
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