Study Suggests Omega Centauri May Have Migrated from Ancient Galactic Merger, But Requires Unusual Bar Dynamics
A new preprint study argues that the globular cluster Omega Centauri may have originated in the Gaia Sausage-Enceladus (GSE) merger event and was subsequently pushed to its current orbit by perturbations from the Milky Way's rotating bar. The GSE was a large dwarf galaxy that merged with the Milky Way billions of years ago, and Omega Centauri has long been suspected to be its former nuclear star cluster. If confirmed, the finding would require revising current estimates of the Galactic bar's rotational speed, which the model demands be significantly slower than most recent measurements suggest.
Submitted to the journal Monthly Notices of the Royal Astronomical Society, the paper investigates why Omega Centauri and the remnant debris of the Gaia Sausage-Enceladus merger occupy very different orbits today, despite the proposed common origin. The authors ran N-body simulations of the GSE debris and Omega Centauri in a realistic Milky Way gravitational potential that includes a decelerating Galactic bar at various pattern speeds. They found that Omega Centauri's orbit can indeed be traced back to the phase-space region occupied by GSE debris, lending dynamical support to the shared origin hypothesis. Chemical evidence — specifically the distribution of alpha-element-to-metal ratios ([α/M]) for stars lying between the GSE debris and Omega Centauri in angular momentum–energy space — tentatively supports the scenario but is described as inconclusive. The critical caveat is that the migration mechanism works only if the bar's present-day pattern speed is at or below approximately 26 km/s/kpc, a value considerably lower than most current observational estimates. The authors conclude that a GSE origin for Omega Centauri is both dynamically and chemically plausible, but stress that accepting it would necessitate a re-evaluation of the consensus on the Milky Way bar's rotation rate.
What's missing
The study acknowledges that the chemical ([α/M]) evidence is inconclusive, but does not quantify the statistical significance of that tentative support. The work is a preprint and has not yet completed peer review.
What different sources said
- arXiv astro-phCenter
Bar-induced migration of $\omega$ Centauri away from Gaia Sausage-Enceladus
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