An extremely metal-deficient globular cluster in the Andromeda Galaxy

TL;DR

This paper reports the discovery of a massive, extremely metal-poor globular cluster in the Andromeda Galaxy, challenging existing theories about the metallicity limits of globular cluster formation.

Contribution

It presents the identification and characterization of the most metal-poor globular cluster known, providing new insights into early galaxy formation and chemical evolution.

Findings

Iron abundance is about 800 times lower than the Sun.

Cluster is strongly depleted in magnesium.

Challenges the metallicity floor concept for globular clusters.

Abstract

Globular clusters (GCs) are dense, gravitationally bound systems of thousands to millions of stars. They are preferentially associated with the oldest components of galaxies, and measurements of their composition can therefore provide insight into the build-up of the chemical elements in galaxies in the early Universe. We report a massive GC in the Andromeda Galaxy (M31) that is extremely depleted in heavy elements. Its iron abundance is about 800 times lower than that of the Sun, and about three times lower than in the most iron-poor GCs previously known. It is also strongly depleted in magnesium. These measurements challenge the notion of a metallicity floor for GCs and theoretical expectations that massive GCs could not have formed at such low metallicities.