Blue Stragglers in NGC 6397

Blue Stragglers in NGC 6397



In our neck of th Galaxy stars are to far apartto be in danger of colliding, but in the dense cores o globular star clusters star collisionsmay be relatively common.In fact researchers have evidence that theclosely spaced blue stars near the center of the above image taken by the orbiting Hubble Space Telescopewere formed when stars directly collided.Pictured is the central region o NGC 6397, globular clusterabout 6,000 light-years distant, whos stars all formed at about the same time NGC 6397'smassive stars have long since evolved off the main sequence,exhausting their central supplies o nuclear fuel.This should leave the cluster with only old low mass stars; faint redmain sequence stars and brighter blue an red giants.However, spectroscopic data show that the indicated stars, descriptivelydubbed blue stragglers, are clearlymain sequence stars which are too blue and too massive to still be there Suggestively the stragglers appear to be two and occasionally threetimes as massive as the lower mass cluster starsotherwise present supporting evidence fortheir formation from two and even three star collisions.