An extremely metal-deficient globular cluster in the Andromeda Galaxy

Understand

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.