How does metal abundance vary between globular clusters near the galactic centre and those in the halo?

In the study of globular clusters, astronomers classify these objects based on their chemical composition, specifically their abundance of heavy elements, which are referred to as metals.1

There is a clear trend in the distribution of these elements: the abundance of metals is higher in globular clusters located near the galactic centre compared to those found in the halo, which represents the outermost reaches of the Galaxy. This variation may suggest that there was a nonuniform distribution of elements throughout the primordial mass from which the Galaxy formed.12

While this pattern exists, the overall chemical makeup of globular clusters remains distinct from the stars found in the galactic plane. Globular clusters are composed of Population II stars, which are characterized by significantly lower metal content—often as little as 0.02 percent by mass—compared to the approximately 2 percent found in the interstellar gas of the solar neighbourhood. Additionally, the history of galactic evolution, including the potential merging of smaller systems, adds complexity to this chemical distribution.132