Hubble Messier 54

This beautiful visible and infrared Hubble image shows what could be just another globular cluster, but this dense group of stars known as M54 was the first globular cluster found outside our galaxy. M54 belongs to a satellite galaxy of the Milky Way called the Sagittarius Dwarf Elliptical Galaxy. When Charles Messier discovered M54 in 1778, he did not know that the cluster belonged to another galaxy.