This artist's impression shows the magnetar in the very rich and young star cluster Westerlund 1. ScienceDaily (Aug. 19, 2010) — 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?