Using ESO's Very Large Telescope, European astronomers have for the first time demonstrated that a magnetar — an unusual type of neutron star — was formed from a star with at least 40 times as much mass as the Sun. The result presents great challenges to current theories of how stars evolve, as a star as massive as this was expected to become a black hole, not a magnetar. This now raises a fundamental question: just how massive does a star really have to be to become a black hole?