A new preprint posted to arXiv investigates whether the giant star cluster Omega Centauri represents the leftover nucleus of a dwarf galaxy that merged with the Milky Way billions of years ago. The authors propose that the stellar debris known as Sequoia, Thamnos, and possibly Gaia-Enceladus all originated from the same parent object, which they call the ω Dwarf. This work has not been peer-reviewed.

The researchers reconstructed the chemical structure of this proposed progenitor by combining stellar abundances from the APOGEE and GALAH surveys with orbital information from the Gaia space telescope. They used orbital energy as a proxy for the stars' original radial positions inside the dwarf galaxy before disruption. The abstract does not specify the sample size or exact number of stars examined, which limits assessment of the statistical power of the findings.

Clear patterns emerged in the data. Chemically evolved stars (younger and enriched in aluminum, nitrogen, and helium) are strongly concentrated in the inner regions near Omega Centauri and Thamnos, consistent with formation during or after the merger. The older, primordial stellar population resembles the chemistry seen in intact dwarf galaxies. The metallicity profile forms an inverted U-shape, matching gradients observed in present-day nucleated dwarf galaxies. Inner regions show higher alpha-element enhancement than the outskirts, suggesting shorter, more intense star formation in the nucleus. Neutron-capture element ratios further indicate an r-process dominated outer region rich in europium, while inner areas display evidence of more delayed and complex enrichment.

The analysis supports an outside-in stripping sequence for Sequoia and Thamnos around Omega Centauri, but the connection to Gaia-Enceladus remains uncertain. The authors conclude that these results strengthen the case for Omega Centauri as the nuclear star cluster of an accreted dwarf galaxy. Source: https://arxiv.org/abs/2603.23589