For more than six decades, the quest to understand the formation of hot (about 20,000−30,000 K) extreme horizontal branch (EHB) stars in Galactic globular clusters has remained one of the most elusive in stellar evolutionary theory. Here we report on two discoveries that challenge the idea of the stable luminosity of EHB stars. The first mode of EHB variability is periodic and cannot be ascribed to either binary evolution or pulsation. Instead, we attribute it here to the presence of magnetic spots: superficial chemical inhomogeneities whose projected rotation induces the variability. The second mode of EHB variability is aperiodic and manifests itself on timescales of years. In two cases, six-year-long light curves display superflare events that are several million times more energetic than solar analogues. We advocate a scenario in which the two EHB variability phenomena are different manifestations of diffuse, dynamo-generated, weak magnetic fields. Magnetism is therefore a key player driving the formation and evolution of EHB clusters stars and, likewise, operating in the Galactic field counterparts. Our conclusions bridge similar variability/magnetism phenomena in all radiative-enveloped hot-stars: young main-sequence stars, old EHBs and defunct white dwarfs.

六十多年来，寻求了解星系球状星团中炽热（约20,000-30,000 K）极水平分支（EHB）恒星的形成一直是恒星演化理论中最难以捉摸的问题之一。在这里，我们报告了两个发现，这些发现对EHB恒星的稳定光度提出了挑战。EHB变异性的第一种模式是周期性的，不能归因于二进制演化或脉动。相反，我们在这里将其归因于磁点的存在：表面化学不均匀性，其预计旋转会引起变化。EHB变异性的第二种模式是非周期性的，并在多年的时间尺度上表现出来。在两种情况下，长达六年的光曲线显示的超耀斑事件比太阳类似物的能量高出几百万倍。我们提倡一种方案，其中两种EHB变异现象是弥散，发电机产生的弱磁场的不同表现形式。因此，磁性是驱动EHB星团的形成和演化的关键因素，并且同样在银河系的对应领域中发挥作用。我们的结论弥合了所有辐射包围的热星类似的变异性/磁性现象：年轻的主序星，老的EHB和已灭绝的白矮星。