Given the the great age of clusters, it was predicted that stars more massive than about 80% the mass of the Sun, the so-called turnoff mass, should have evolved to later stages of stellar life, ultimately "dying" off as a dim stellar remnant such as a white dwarf, neutron star, or black hole. Nevertheless, when one observes a globular cluster, a number of bluish main-sequence stars, more massive than the turnoff mass, are seen scattered throughout. These "blue stragglers" appear to 'straggle' behind in their evolution, since, despite being more massive than the turnoff mass, they have not yet left the main-sequence.
The calculations performed by Alexander Brown '09 and Lombardi help establish that these exotic blue stragglers can indeed be formed through the collision of garden-variety main-sequence stars in a cluster.
