This image may not be used by or to promote the arms, nuclear power or tobacco industries or any religious organisation, or in any discriminatory way, or to imply the endorsement by ESO of any product, service or activity Conceptual illustration showing a giant magnetic spot (top, white) on the surface of an extremely hot star, known as an extreme horizontal branch star. This spot is caused by magnetic fields. As the star rotates, the spot comes and goes causing variation in the brightness of the star.