A binary origin for ‘blue stragglers’ in globular clusters

The origin of blue stragglersTheoretically the abnormally blue and massive stars known as blue stragglers should have evolved off the main stellar sequence and died long ago. But they are still to be found in globular clusters. Two scenarios to account for their presence have been suggested — direct stellar collisions or binary evolution. A new analysis of the data from known blue stragglers reveals a clear, but sublinear, correlation between the number of blue stragglers in a cluster core and the total stellar mass contained within it. This finding favours binary systems as the source for blue stragglers.