Co-author Jeremy Drake said: “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.” Let the head-scratching begin.
Observations confirm that the closest star to our solar system has a regular magnetic cycle similar to our Sun, reports Sky & Telescope.
With the recent discovery of a potentially habitable planet around Proxima Centauri, astronomers have been studying this star with renewed fervor. Part of their attention focuses on the star’s behavior. M dwarfs are notorious for their flares, and such stellar tantrums could be deadly for budding life on nearby planets.
But it’s only the young M dwarfs that are truly “flare stars.” Proxima Centauri, on the other hand, is roughly 5 billion years old (we think), and although it certainly flares, we’re not sure what its long-term activity is at such a respectable age. One thing astronomers thought they knew, though, was that such stars wouldn’t have regular magnetic cycles like we see on the Sun.
Our star goes through an 11-year sunspot cycle as its global field flips directions, but that shouldn’t happen on little stars like Proxima. Or so we thought. Now both observations and computer simulations confirm that, contrary to expectation, Proxima Centauri and stars like it do have regular magnetic cycles.
A Cycle for Proxima Centauri
Previous observations have explored whether Proxima Centauri has an activity cycle, with some suggesting that it does. Inspired by an article he saw about one of these studies in 2007 in Sky & Telescope, Bradford Wargelin (Harvard-Smithsonian Center for Astrophysics) decided to investigate whether hints of a cycle were real. (At the time he didn’t buy it.)
Wargelin and his colleagues amassed optical, ultraviolet, and X-ray observations of the star from ground- and space-based telescopes, spanning 22 years. The UV and X-ray photons generally come from flares, and cyclic variations at these wavelengths are a lot more obvious than those in optical.
The team found that, yep, Proxima Centauri has a 7-year cycle, with the X-rays and UV going up when the optical brightness goes down — as would be expected if the star is plastered in starspots (dimming its optical brightness) during times of heightened activity. The 7-year cycle agrees well with previous studies that narrowed in on a 7- to 8-year range. (Incidentally, the study mentioned in S&T argued for a 1.2-year cycle, which Wargelin’s team disproved.)
[For further technical discussion and info. see link below]