Proxima Centauri Has A Starspot Cycle Just Like Our Sun

An artist's impression of what the interior of Proxima Centauri looks likes. NASA/CXC/M.Weiss

Proxima Centauri has been in the news a lot lately after the discovery of an Earth-sized planet called Proxima b in its habitable zone, and now scientists have discovered a new unexpected feature. The red dwarf star Proxima has a regular cycle of starspots.

Researchers from the Harvard-Smithsonian Center for Astrophysics and the University of Warsaw found that the small red dwarf has a 7-year stellar cycle, meaning it has starspots similar to our own Sun's sunspots. This discovery is very surprising as astronomers didn’t think stars this small were able to create starspots in the first place.

"The existence of a cycle in Proxima Centauri shows that we don't understand how stars' magnetic fields are generated as well as we thought we did," co-author Jeremy Drake said in a statement.

Starspots are created by the powerful magnetic fields inside stars. They are regions slightly cooler than the surrounding material and, for this reason, they appear darker. Stars are made of electrically charged material known as plasma, and as the plasma is moved around it creates strong magnetic fields.

Most stars have a relatively still interior and a convective exterior; the plasma in the outer layer moves up and down like boiling water in a pot. The regular magnetic cycle is generated by the interaction between the two layers.

The Sun has an 11-year cycle where it goes from having no spots to more than 100 of them covering about 1 percent of its surface.

Stars the size of Proxima Centauri, which is one-tenth as massive as the Sun, are convective all the way to their core, so they should have a spot cycle. In the paper, published in the Monthly Notices of the Royal Astronomical Society, the team illustrates substantial evidence indicating a regular starspot cycle that can end up covering 20 percent of the star's surface.

"If intelligent aliens were living on Proxima b, they would have a very dramatic view," said lead author Brad Wargelin in the statement.

The presence of a regular cycle might have important implications for the presence of life in the system, too. Proxima b is only 7 million kilometers (5 million miles) from Proxima Centauri, so a powerful magnetic field could profoundly affect the habitability of the planet, perhaps making it less likely.

"Direct observations of Proxima b won't happen for a long time. Until then, our best bet is to study the star and then plug that information into theories about star-planet interactions," concluded co-author Steve Saar.

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