An extremely metal-deficient globular cluster in the Andromeda Galaxy

Abstract

A relic star cluster under the floor Globular clusters (GCs) are gravitationally bound assemblies of thousands to millions of stars that orbit in the outskirts of large galaxies. GCs consist of old stars with low metallicity containing low proportions of chemical elements heavier than hydrogen and helium. However, GCs appear to have a minimum metallicity, known as the floor, implying that at least some of those elements were required for their formation. Larsen et al. have found a GC in the nearby Andromeda Galaxy with a metallicity beneath the floor. This unexpected discovery will inform models of GC formation and incorporation into galaxies. Science , this issue p. 970