Note:  Press release from Harvard-Smithsonian Center for Astrophysics.

Bob Eklund
Looking Up

In August, astronomers announced that the nearest star, Proxima Centauri, hosts an Earth-sized planet (called Proxima b) in its habitable zone. At first glance, Proxima Centauri seems nothing like our Sun. It’s a small, cool, red dwarf star that’s only one-tenth as massive and one-thousandth as luminous as the Sun. However, new research by Harvard-Smithsonian Center for Astrophysics shows that it is Sun-like in one surprising way: It has a regular cycle of starspots.

Starspots (like sunspots) are dark blotches on a star’s surface where the temperature is a little cooler than the surrounding area. They are driven by magnetic fields. A star is made of ionized gases called plasma. Magnetic fields can restrict the plasma’s flow and create spots. Changes to a star’s magnetic field can affect the number and distribution of starspots.

Our Sun experiences an 11-year sunspot activity cycle. At the solar minimum, the Sun is nearly spot-free. At solar maximum, typically more than 100 sunspots cover less than one percent of the Sun’s surface.

The new study finds that Proxima Centauri undergoes a similar cycle lasting seven years from peak to peak. However, its cycle is much more dramatic. At least a full one-fifth of the star’s surface is covered in spots at once.