It took more than 200 years to find out, but a globular cluster discovered in 1778 by comet-hunter Charles Messier turned out to be the first such star swarm located outside the Milky Way. As astronomers discovered in 1994, the cluster, known as M54 in Messier’s famous catalogue, is actually located some 90,000 light years away in the Sagittarius Dwarf Elliptical Galaxy, about three times farther than Earth is from the center of the Milky Way. But if you wait a while – a very long while – M54 will become part of Earth’s galaxy as the Sagittarius dwarf slowly merges with the larger body. This photograph of M54 was taken in 2011 by the Hubble Space Telescope’s Advanced Camera for Surveys.
An international research team of astronomers has, for the first time, found young populations of stars within globular clusters that have apparently developed courtesy of star-forming gas flowing in from outside of the clusters themselves. This method stands in contrast to the conventional idea of the clusters’ initial stars shedding gas as they age in order to spark future rounds of star birth.
Globular clusters offer some of the most spectacular sights in the night sky. These ornate spheres contain hundreds of thousands of stars, and reside in the outskirts of galaxies. The Milky Way contains over 150 such clusters — and the example shown in this NASA/ESA Hubble Space Telescope image, named NGC 362, is one of the most unusual ones.