An international collaboration of astrophysicists, involving the CEA, the CNRS and the University Paris-Diderot, has succeeded in determining the presence of strong magnetic fields in the heart of giant red stars that vibrate like the sun. By studying the waves generated at the surface of hundreds of red giant stars, scientists were able to probe the interior of the stars and reconstitute their structures (this is the principle of asteroseismology), characterizing in particular the internal magnetic phenomena. They were thus able to discover the existence of an internal magnetic field up to 10 million times higher than that generated at the heart of the Earth. These results will allow researchers to better understand the evolution of stars where the magnetic field plays a fundamental role. They are published in Science on 23 October 2015.