Stars in globular clusters are generally believed to have all formed at thesame time, early in the Galaxy's history. 'Blue stragglers' are stars massiveenough that they should have evolved into white dwarfs long ago. Two possiblemechanisms have been proposed for their formation: mass transfer between binarycompanions and stellar mergers resulting from direct collisions between twostars. Recently, the binary explanation was claimed to be dominant. Here wereport that there are two distinct parallel sequences of blue stragglers inM30. This globular cluster is thought to have undergone 'core collapse', duringwhich both the collision rate and the mass transfer activity in binary systemswould have been enhanced. We suggest that the two observed sequences arise fromthe cluster core collapse, with the bluer population arising from directstellar collisions and the redder one arising from the evolution of closebinaries that are probably still experiencing an active phase of mass transfer.
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