Globular Clusters are tightly packed collections of hundreds of thousands of very old stars, spherically distributed around the Milky Way Galaxy.  They undergo little change, have nearly no gas, and have a stellar density way higher than the rest of the Galaxy.  The first one discovered, in 1665, is messier 22, one of the most well studied, easily visible, and interesting globular clusters. Based on observations, this globular cluster contains at least two black holes. It is also one of only three globular clusters ever found to host a planetary nebula, a gaseous shell emitted by a dying star with...