The Pure Noncollisional Blue Straggler Population in the Giant Stellar System ω Centauri

We have used high spatial resolution data from the Hubble Space Telescope (HST) and wide-field ground-based observations to search for blue straggler stars (BSS) over the entire radial extent of the large stellar system ω Centauri. We have detected the largest population of BSS ever observed in any stellar system. Even though the sample is restricted to the brightest portion of the BSS sequence, more than 300 candidates have been identified. BSS are thought to be produced by the evolution of binary systems (either formed by stellar collisions or mass exchange in binary stars). Since systems like Galactic globular clusters (GGC) and ω Centauri evolve dynamically on time-scales significantly shorter than their ages, binaries should have settled toward the center, showing a more concentrated radial distribution than the ordinary, less massive single stars. Indeed, in all GGCs which have been surveyed for BSS, the BSS distribution is peaked at the center. Conversely, in ω Centauri we find that the BSS share the same radial distribution as the adopted reference populations. This is the cleanest evidence