Massive planets with close-in orbits — also known as hot Jupiters — may influence the rotation and surface activity of their host stars.

Katja Poppenhaeger and Scott Wolk at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, analysed the emissions of binary-star systems, in which only one of the two stars in the system hosted an exoplanet. Comparing the differences between the emissions of the stars in each pair allowed the authors to measure the influence of the exoplanet on its host star. Using X-ray data from the Chandra and XMM-Newton space telescopes, the researchers found that the stars hosting hot Jupiters showed more magnetic activity than their planet-free companions.

Magnetic activity increases with rotation, so the authors suggest that the gravitational influence of the hot Jupiters may have counteracted the natural slowing of their host stars' spin over time.

Astron. Astrophys. 565, L1 (2014)