Some stars have a magnetic field, such as our Sun. This magnetic field can interact with the magnetic field of the planets around it, just like the Sun-Earth pair. In their search for exoplanets, some astrophysicists study the magnetic interactions with their host star.
In this interview, the astrophysicist Antoine Strugarek explains what happens when a planet is magnetically coupled with its star.
For more information: Solar storms and the magnetic coupling generate magnificent displays on Earth: the polar aurorae (borealis in the North and australis in the South). Particles are ejected from the Sun at high speeds during solar flares and spread out into space. When they encounter the Earth’s magnetosphere, the magnetic field lines are distorted and break up, joining up again on the other side of the Earth (opposite from the Sun). The solar energy particles trapped in these lines are then catapulted towards the Earth’s poles, where they excite the atoms in the atmosphere at different altitudes. As they become de-excited, these atoms emit light. Auroras can also be seen on other planets in the Solar System.
NASA has produced a compilation of polar aurorae. You can also admire these aurorae in 3D thanks to an “Art-sciences” project called Aurora3D, produced by a team at the Paris Astrophysics Institute (IAP).