Blue straggler populations beyond the Milky Way
  Although the formation of blue straggler stars (BSSs) is routinely attributed
to stellar interactions in binary systems, the relative importance of the
direct collision and slow(er) stellar coalescence formation channels is still
poorly understood. We selected a sample of 24 Magellanic Cloud star clusters
for which multi-passband Hubble Space Telescope images are available to address
this outstanding question. We compiled a BSS database, containing both
traditional and evolved BSSs. We found a robust correlation between the number
of BSSs in a cluster's core and its core mass, $N_{\rm BSS, core} \propto
M_{\rm core}^{0.51 \pm 0.07}$, which supports the notion that BSS formation is
linked to a population's binary fraction. At low stellar collision rates, the
mass-normalised number of BSSs does not appear to depend on the collision rate,
which implies that the coalescence-driven BSS formation channel dominates.
Comparison with simulations suggests that stellar collisions contribute less
than 20% to the total number of BSSs formed.
