HST image of an old globular star cluster in galaxy M31

We believe our HST observations of NGC 4038/4039 and other merger galaxies also shed some new light on how young globular clusters form, i.e., from giant clouds of hydrogen gas that astronomers call Giant Molecular Clouds. Full-grown spiral galaxies like the Milky Way have typically 1000-2000 such clouds. An example is the GMC associated with the Eagle Nebula.