Milky Way globular clusters with at least one published IMBH mass estimate or upper limit, side by side. How does Omega Centauri compare to its peers as an IMBH candidate?
| Cluster ↕ | Total mass ↕ | r_h ↕ | Age ↕ | IMBH estimate ↕ |
|---|
Only Milky Way globular clusters with at least one published IMBH mass estimate or upper limit appear in the table. Absence of an IMBH claim ≠ absence of an IMBH — most GCs have never been kinematically resolved at the centre with the precision needed to test the hypothesis, and many lack pulsars suitable for timing constraints. This tool is not a survey of all GCs.
Every cluster in this table has at least one published claim of an IMBH, but very few are uncontested. The pattern across the literature is consistent: initial detections from integral-field stellar kinematics tend to get challenged by subsequent re-analyses with better-resolved cluster centres or independent constraints (radio, pulsar timing). Whether any globular cluster hosts a confirmed IMBH is itself debated. Omega Centauri's Häberle 2024 lower bound is the most recent prominent positive claim; it remains in tension with the Bañares 2025 upper limit derived from the same source.
The table assigns each cluster the most recent/canonical claim, but the IMBH literature for any of these objects typically contains contradictory results. Click a row to read the brief context note. For Omega Centauri specifically, the full history is in the IMBH Measurement Timeline and the synthesis view is in the Constraint Stacker.
Cluster bulk properties (total mass, half-light radius, age) from Baumgardt & Hilker (2018, MNRAS 478:1520) unless noted. IMBH estimates from individual papers as cited per row. Values curated in tools/data/measurements.js (CC0).
The Milky Way hosts approximately 157 known globular clusters (Harris 1996/2010 catalog as updated by Baumgardt & Hilker 2018 and ongoing Gaia work). Of these, only ~10 have published IMBH mass claims or meaningful upper limits — the table here shows the most-cited six. The remaining ~150 are either too distant for kinematic resolution at the centre, lack suitable pulsar populations for timing, or have no published radio non-detections at the relevant sensitivity. Searching for IMBHs in GCs is observationally expensive: each candidate requires HST-tier astrometry over multiple epochs OR access to a southern-hemisphere radio array.
Every cluster in this table has at least one published detection — and every detection has at least one contesting paper. NGC 6388 (Lützgendorf 2011 → 1.7×10⁴ M☉) was challenged by Cseh et al. 2010 radio non-detection. 47 Tuc (Kızıltan 2017 → 2,300 M☉ from pulsar timing) was disputed by Mann et al. 2019 N-body modelling favouring stellar-mass remnants. M54 (Ibata 2009 → 9,400 M☉) is complicated by being the nuclear cluster of the Sagittarius dwarf galaxy. M15 (Gerssen 2002 detection → Kirsten & Vlemmings 2012 upper limit). The pattern is consistent: GCs are dense enough to plausibly host IMBHs but kinematically degenerate enough that single-technique detections rarely survive multi-technique scrutiny.
Omega Centauri is the Milky Way's most massive cluster at 4×10⁶ M☉ — five times more massive than the next runner-up (NGC 6388). It is also unusual in hosting multiple distinct stellar populations (3+ chemically-distinct subpopulations identified spectroscopically), consistent with it being the stripped nuclear cluster of a dwarf galaxy accreted by the Milky Way long ago. Combined with its relative proximity (5.4 kpc) and southern declination (accessible to MeerKAT, ALMA, VLT), OC is the single best-studied IMBH candidate in the Milky Way and the natural anchor for any IMBH-population mass-function claim.