Researchers from the Centre de Physique théorique (CNRS/Polytechnique) and the Laboratoire Astrophysique, interprétation-modelling (CNRS/CEA/Paris Diderot University) have identified a key phenomenon in the triggering of solar flares. Using satellite data and models, the researchers were able to monitor the evolution of the solar magnetic field in an area with eruptive behaviour. Their calculations reveal the formation of a magnetic string that emerges from inside the Sun and is associated with the appearance of a sunspot. They show that this structure plays an important role in triggering the eruption. By characterizing the transition to the eruption, this work opens the way to predicting solar storms that affect the Earth. They made the front page of Nature magazine on October 23.