Here is a bit more information on this particular discovery:

The stars in the cluster all formed around the same time out of the same gas cloud. These sibling stars are only bound together very loosely by their attraction to one another and also by the gas between them.

Awesome!  The team at ESO keeps coming up with incredible new pics from space!  And here is an intro on a cool related video:

There are two types of star clusters. Open (or galactic) clusters are sparsely populated, fairly young groups of tens to hundreds of stars that have formed out of a nebula and that are slowly “evaporating” into space. Globular clusters are very old, densely packed groups of millions of star on the outskirts of galaxies. This program combines 3 ESA videos with news about Star Clusters:
1. Extreme star cluster;
2. Globular Clusters;
3. Omega Centauri

thanks to sci-news.com for the great info

thanks to eso for the pic