Hubble sees multigenerational cluster NGC 2419

This image from the NASA/ESA Hubble Space Telescope shows globular star cluster NGC 2419. The globular clusters are beautiful and majestic. They are globular clusters of stars orbiting the center of a galaxy, and in the case of NGC 2419, that galaxy is our own Milky Way. NGC 2419 lies about 300,000 light-years away from the Solar System in the constellation of the Lynx.

The stars that inhabit globular clusters are very similar because they formed around the same time. Astronomers can determine a star’s relative age by its chemical composition, a property called metallicity. Because the stars in a globular cluster all formed around the same time, they tend to exhibit similar properties. Astronomers believe that this similarity includes the stellar helium content. They believed that all stars in the globular cluster would contain similar amounts of helium.

However, Hubble observations of NGC 2419 revealed that this is not always the case. This globular cluster contains two separate clusters of red giant stars, and one is unusually helium-rich. NGC 2419’s stars contain various other elements as well. In particular, their nitrogen content varies. To make things even more interesting, helium-rich stars are mostly in the globular cluster center and spin. The Hubble observations have raised questions about the formation of globular clusters. Did these two radically different groups of stars form together? Or did this globular mass originate by a completely different path?