Nuclear star clusters are the surviving nuclei of tidally stripped dwarf galaxies — exactly the origin channel proposed for Omega Centauri. Compare OC's structural parameters against well-characterized NSCs to ask: is OC a typical stripped nucleus, or something special?
Omega Centauri is highlighted in teal. NSCs (nuclear star clusters confirmed as stripped nuclei) in amber. Regular globular clusters in grey for comparison. Key discriminators: OC's multi-population metallicity spread and retrograde orbit are distinctive NSC signatures. The BH mass fraction (M_BH/M_cluster) is the key quantity for IMBH formation probability.
| Object | Type | Mass (M☉) | Reff (pc) | Σ0 (M☉/pc²) | Age (Gyr) | [Fe/H] spread | MBH (M☉) | BH fraction | IMBH status |
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NSCs and GCs follow different mass–size scaling relations. OC's position on this diagram reveals whether it aligns with the NSC branch or the GC branch — a key diagnostic for its formation channel.
Nuclear star clusters (NSCs) in dwarf galaxies have: (1) multiple stellar populations spanning wide metallicity ranges (ΔFe/H > 0.5 dex), (2) central surface densities Σ₀ > 10⁴ M☉/pc², (3) a host galaxy origin that gives them retrograde or eccentric orbits in the Milky Way if accreted. Omega Centauri satisfies all three: it shows ΔFe/H > 1.5 dex, Σ₀ ~ 10⁵ M☉/pc², and a retrograde Galactic orbit — strongly suggesting a stripped nucleated dwarf origin (Bekki & Tsujimoto 2003; Hilker & Richtler 2000).
NSCs preferentially harbor massive black holes (Neumayer et al. 2020). The BH mass fraction in the table shows the ratio of IMBH/SMBH mass to cluster mass — for OC, even at the lower Bañares-Hernández (2025) limit of 6,000 M☉, the ratio is ~0.15%, consistent with the high end of the NSC–BH mass relation. This is significantly above typical GC BH fractions.
Neumayer, Seth & Böker 2020 (A&ARv 28:4) · Seth et al. 2006 (AJ 132:2539) · Bekki & Tsujimoto 2003 (MNRAS 340:L29) · Baumgardt & Hilker 2018 (MNRAS 478:1520) · Ibata et al. 2009 (ApJ 699:L169)