IMBH Growth History

Seed to ≥8,200 M☉ in 12 billion years. Dial the three growth channels and watch ωCen's black hole assemble itself across cosmic time.

🔬 Established Astrophysics ⚠ Channel Mix Modeled
Mass tension: Häberle et al. 2024 gives ≥8,200 M☉ (lower bound, stellar kinematics). Bañares-Hernández et al. 2025 gives ≤6,000 M☉ (upper bound, kinematics + pulsar timing; A&A 693:A104). Both are displayed as target bands on the chart.
Three channels have been proposed for IMBH growth in dense clusters. Runaway stellar collisions — massive stars merge repeatedly before the first supernovae, forming a very massive star that collapses to a seed of ~10²–10³ M☉ within the first few Myr. Tidal disruption events (TDE) — stars scattered onto loss-cone orbits are torn apart and accreted, building mass over Gyr. Binary BH mergers — gravitational-wave capture and dynamical hardening produce repeated mergers, each adding one BH mass.
Growth Channel Weights
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Mass Accumulation — Lookback Time

Solid line = total mass. Shaded band = Häberle (lower, orange) / Bañares-Hernández (upper, red) observed constraints. Formation epoch: ~12 Gyr ago.

Today's Budget
Final Mass
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From TDE Accretion
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From BH Mergers
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Constraint Match
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Runaway stellar collisions (Portegies Zwart & McMillan 2002): in a young, dense cluster, the most massive stars sink to the centre by dynamical friction faster than they evolve. They undergo successive mergers, forming a very massive star (VMS) of ~100–1,000 M☉ that collapses directly to an IMBH. This channel operates in the first ~3 Myr and sets the seed mass.

Tidal disruption events: stars scattered by two-body relaxation onto loss-cone orbits are disrupted and partially accreted. The rate depends on the stellar density cusp, the cluster relaxation time, and the BH mass itself (higher mass → larger capture cross-section but smaller loss cone in phase space). The net accretion is modelled here as a constant rate over the cluster lifetime (~12 Gyr); real rates likely declined as the core was depleted.

Binary BH mergers: stellar-mass BHs form from cluster supernovae. Dynamical friction causes them to segregate to the centre, where they form binaries and harden via three-body interactions. When the binary becomes hard enough, gravitational-wave emission drives a merger. The mass added per event = q × M_current; the BH then receives a natal kick (partially modelled here as recoil loss — a fixed 5% GW kick mass loss is included).

González Prieto, Rodriguez & Cabrera (2025) modelled the full channel mix for ωCen using Monte Carlo N-body simulations with detailed loss-cone dynamics, finding TDE accretion and compact-object mergers are both required to reach the Häberle mass floor, with seeds of 500–5,000 M☉ growing to ~50,000 M☉ over 12 Gyr. The 2026 A&A results (Mapelli et al.) show that seed formation in low-metallicity clusters — as ωCen was — is especially efficient.

References: González Prieto, Rodriguez & Cabrera 2025, ApJL (arXiv:2507.06316) · Häberle et al. 2024 Nature 631:285 · Bañares-Hernández et al. 2025 A&A 694:A107 · Portegies Zwart & McMillan 2002 ApJ 576:899