When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole behind. For a long time, scientists have suspected that the liberated electron and the positively charged hole form a new kind of quasiparticle—known as ‘core-exciton’. But so far, there has not yet been a real proof of its existence. Scientists have a wide range of tools to track excitons in semiconductors in real-time. Those are generated by ordinary light, and can be employed in various applications in optoelectronics and microelectronics. On the contrary, core-excitons are extremely short-lived, and up to now, no technique was available to track their motion and deduce their properties.