The red dwarf is called AU Microscopii (or AU Mic) and, because of its relative proximity, it is considered to be one of the best-studied of the approximately 150 billion red dwarfs in our Milky Way galaxy. Red dwarfs are the smaller and cooler cousins of stars like our Sun, making up more than 70 percent of the stellar population in our galaxy.
Red dwarfs are very active and often show intense variability in their emission of high-energy radiation. This variability is caused by the periodic growth and decay of starspots – areas of intense magnetic activity that are similar to sunspots on our Sun.
On other types of stars, starspots typically emerge and decay over a few months to a few years. However, in the case of AU Mic, our observations show that the starspot cycle may last 11 years, which is not too different from the time it takes the Sun's sunspot cycle to complete. This is intriguing because AU Mic rotates about 20 times faster than the Sun and thus scientists do not completely understand why the two objects should host activity cycles of similar timescale.
It is interesting to note that, during the observing campaign, the starspot on AU Mic disappeared and then reappeared, which is similar to what happens to the Sun's polar magnetic fields before a complete polarity flip occurs (called a pole reversal). Polar reversals are the process that generates the Earth's geomagnetic field and it was hypothesized that red dwarfs undergo similar behavior, but until now it had never been observed.
Further observations are needed to confirm if the current behavior of AU Mic is indeed the result of the emergence of a new cycle, or if it's a more complicated process that happens more sporadically. Continued monitoring of red dwarfs will eventually allow scientists to better understand how their activity cycles work. Ultimately, this will reveal the connections between the physical properties of stars and the habitable zones around them.
The research was accepted for publication in The Astronomical Journal.
