The Dwarf-Galaxy Inheritance

The Milky Way's gravitational tides peel a satellite dwarf from the outside in. The diffuse stellar envelope disperses into halo streams (Sequoia, Thamnos, Gaia-Enceladus debris); the dense, gravitationally bound nucleus survives. If the progenitor was massive enough and the pericentre tight enough, only the nucleus is left in the present day — and that nucleus is what we now call ω Cen. The slider replays this disruption schedule from t = 12 Gyr ago to today.

Ordinary globular clusters host a single stellar population — one age, one metallicity, one chemical pattern. ω Cen famously hosts at least three, with [Fe/H] spreading over more than a dex. That kind of internal chemical inhomogeneity is the photometric receipt for an extended star-formation history — i.e. a dwarf galaxy's, not a cluster's. Toggle the "show multi-population" mode to see the second and third sequences split off the main isochrone.

Two-body relaxation in a dense nucleus drives heavy stellar remnants (≈ 10 M⊙ stellar BHs) toward the centre. Once concentrated, they begin to merge — and if the natal-kick retention fraction is high enough, the merger product can run away to >rsim 10³ M⊙ before the cluster relaxes. The dwarf-galaxy nucleus scenario favours this channel because its deeper potential better retains stellar BHs against natal kicks. Whether the channel opens depends on the retention slider.

Now look at the constraint stacker with a properly informed prior. Häberle 2024's ≈ 8,200 M⊙ sits exactly where the runaway-merger channel would deposit an IMBH for a dense, deep-potential dwarf nucleus — which is to say, where the formation-channel argument predicts it to be. Bañares 2025's upper limit (< 6,000 M⊙) is in tension with both Häberle and the formation-channel prior. The right experiment to resolve this is the one in Demo K.