Blue straggler stars: The spectacular population in M80

Using Hubble Space Telescope WFPC2 observations in two ultraviolet (UV) fil ters (F225W and F336W) of the central region of the high-density Galactic g lobular cluster (GGC) M80, we have identified 305 blue straggler stars (BSS ), which represents the largest and most concentrated population of BSS eve r observed in a GGC. We also identify the largest clean sample of evolved B SS yet found. The high stellar density alone cannot explain the BSS, and we suggest that in M80 we are witnessing a transient dynamical state, during which stellar interactions are delaying the core-collapse process leading t o an exceptionally large population of collisional BSS.