A double cluster at the core of 30 Doradus
  Based on an analysis of data obtained with the Wide Field Camera 3 (WFC3) on
the Hubble Space Telescope (HST) we report the identification of two distinct
stellar populations in the core of the giant HII region 30Doradus in the Large
Magellanic Cloud. The most compact and richest component coincides with the
center of R136 and is ~1 Myr younger than a second more diffuse clump, located
~5.4 pc toward the northeast. We note that published spectral types of massive
stars in these two clumps lend support to the proposed age difference. The
morphology and age difference between the two sub-clusters suggests that an
ongoing merger may occurring within the core of 30Doradus. This finding is
consistent with the predictions of models of hierarchical fragmentation of
turbulent giant molecular clouds, according to which star clusters would be the
final products of merging smaller sub-structures.
