An extremely metal-deficient globular cluster in the Andromeda Galaxy

Area of Science:

• Astronomy and Astrophysics
• Cosmochemistry

Background:

• Globular clusters (GCs) are ancient stellar systems crucial for understanding galactic chemical evolution.
• Their composition provides insights into early Universe element synthesis.

Purpose of the Study:

• To report the discovery and characterization of a massive globular cluster with exceptionally low metallicity.
• To investigate the implications of such a finding for GC formation theories and early galactic chemical enrichment.

Main Methods:

• Spectroscopic analysis of the globular cluster RBC EXT8 in the Andromeda Galaxy (M31).
• Abundance measurements of heavy elements, specifically iron and magnesium.

Main Results:

• Discovery of RBC EXT8, a massive GC in M31, with an iron abundance ~1/800 of the Sun.
• RBC EXT8 exhibits extreme depletion in heavy elements, including magnesium, and is significantly more iron-poor than previously known GCs.
• Its metallicity is lower than the theoretically expected metallicity floor for massive GCs.

Conclusions:

• The existence of RBC EXT8 challenges the concept of a metallicity floor for globular clusters.
• These findings necessitate revisions to theoretical models of massive GC formation in the early Universe.