Hubble has observed a multigenerational cluster

 The Hubble Space Telescope has observed a multigenerational cluster, NGC 2419. It is a globular cluster about three hundred thousand light-years from the solar system in the constellation Lynx. Unlike typical star clusters, whose stars are all of roughly similar age, NGC 2419 appears to be populated by stars belonging to quite different generations.

Stars in globular clusters are generally very similar to each other because they were born around the same time. Astronomers can determine the relative age of a star based on its chemical composition, more specifically by knowing a property called ‘metallicity.’

The globular cluster NGC 2419 imaged with the NASA/ESA Hubble Space Telescope. Credits: .ESA/Hubble & NASA, S. Larsen et al.

Precisely because the stars in a globular cluster all formed at about the same time, they tend to exhibit similar properties. In particular, this similarity was thought to include their stellar helium content. In other words, they thought that all stars in a globular cluster contained similar amounts of helium. However, Hubble observations of NGC 2419 revealed that this is not always the case! This globular cluster contains two separate populations of so-called ‘red giant’ stars; one of which is strangely rich in helium. Variations in the content of other elements including mainly nitrogen have also been detected