Evrim Yazgin
Cosmos science journalist
Astronomers have discovered that binary pairs of stars orbiting each other closely can have unusually high levels of magnetic activity which in our star, the Sun, is responsible for sunspots and solar flares.
Magnetic activity in stars is usually the result of how fast the star is rotating. The faster a star spins, the more magnetic activity – up to a limit where magnetic activity appears to max out.
But new findings published in the journal Nature Astronomy suggest that binary stars also exhibit these magnetic effects.
The results are based on observations from China’s Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) telescope and the Gaia space observatory controlled by the European Space Agency.
Astronomers from Australia and internationally studying the data found that binary stars break the rules of magnetic activity.
Instead of magnetic activity leveling off with higher rotation speeds – as with single stars – binary stars have even stronger magnetic activity. Then, in extreme cases where stars in a binary system spin especially fast (rotation more than twice per day) – the magnetic activity begins to fall – a process called “supersaturation”.
The astronomers say finding the cause of supersaturation is difficult, not least because these stars are spinning 50 times faster than the Sun – the model for understanding magnetic activity of other stars.
“Our results highlight the need for improved observations of stars with properties that are extreme compared with the Sun’s – understanding these extreme cases will shed light on the underlying physical mechanisms,” they write.
They suggest that a possible explanation is that there are tidal forces on the surface of closely-orbiting binary stars due to the gravity of their partner star. These forces might be amplifying or reshaping the magnetic behaviour.
Understanding these magnetic effects could offer new insight into stellar evolution as well as factors which might impact the habitability of exoplanets.
