The star cluster Westerlund 2 is one of the most massive young star clusters known in the Milky Way. New data taken with the Hubble Space Telescope allowed Peter Zeidler to study the very young low mass stars in the dense center. These low mass stars are so young that they have not even started nuclear fusion in their center and still reside on the pre main sequence. Surprisingly two clumps were found with an age of less than 2 Myr.
This data of this program was used for Hubble’s 25th birthday image. Zeidler et al. (2015), published in AJ.