Star cluster Westerlund 1
Using ESO”â„¢s Very Large Telescope (VLT), 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?
To reach their conclusions, the astronomers looked in detail at the extraordinary star cluster Westerlund 1, located 16 000 light-years away in the southern constellation of Ara (the Altar). From previous studies, the astronomers knew that Westerlund 1 was the closest super star cluster known, containing hundreds of very massive stars, some shining with a brilliance of almost one million suns and some two thousand times the diameter of the Sun (as large as the orbit of Saturn).
Says Ben Ritchie, lead author of the paper reporting these results: “If the Sun were located at the heart of this remarkable cluster, our night sky would be full of hundreds of stars as bright as the full Moon.”Â A magnetar is a type of neutron star with an incredibly strong magnetic field “” a million billion times stronger than that of the Earth, which is formed when certain stars undergo supernova explosions.
Credit: ESO/L CalÃƒÂ§ada