Astronomers show that red dwarf star’s magnetic field may be nearing polar reversal

The 11-year solar cycle is a well-known phenomenon during which the strength of the Sun’s magnetic field changes and its polarity reverses. Over the past 30 years, astronomers have seen similar behavior in several Sun-like stars. However, so far no reversal of magnetic polarity has been observed in their cooler counterparts, red dwarfs.

Now, an international team including scientists from the CNRS (including IRAP) has shown that the magnetic field of the highly active red dwarf star AD Leonis may be approaching polar reversal. These data were acquired using the ESPaDOnS (1) and SPIRou (2) instruments of the Canada-France-Hawaii Telescope (CFHT) and the NARVAL (3) instrument of the Bernard Riot Telescope (BLT).Here are the findings: published in a diary astronomy and astrophysics.

AD Leonis is a notoriously active red dwarf star with a magnetic field about 1,000 times stronger than the Sun’s. Although evidence for active cycles exists, it is not yet known whether red dwarfs can exhibit magnetic cycles.

AD Leonis has been observed with the ESPaDOnS and NARVAL instruments since 2006, and with SPIRou since 2019. This research was led by Dr. IRAP. student Stefano Bellotti showed that not only did the magnetic field strength continually decrease over this period, but also that the star’s magnetic poles began to reverse. Although the polarity did not reverse during SPIRou’s observations, these results indicate that red dwarf stars like AD Leonis may experience magnetic cycles similar to the Sun.

The results help improve our understanding of the generation of magnetic fields in stars that are cooler than the Sun. Additionally, studying the magnetic fields of red dwarfs, which are prime targets for detecting rocky Earth-like exoplanets, is essential to understanding the space environment in which rocky exoplanets orbit.