Demo · Physics & Geometry

Reconnection vs. BZ: Which Channel Wins?

Three tools trace the two parallel energy extraction channels from OC’s Kerr IMBH — and show when plasmoid reconnection overtakes the Blandford-Znajek jet.

3 tools · ~10 min · Meringolo et al. 2025
⚙ Choose a spin regime

Each scenario pre-loads all three tools with the spin parameter that defines which extraction channel dominates. Walk the chain to see how the balance shifts.

01
Step 1 · Spacetime Structure
The Ergosphere Boundary

The Blandford-Znajek mechanism and magnetic reconnection both operate in or near the ergosphere — the region outside the event horizon where spacetime rotation is compulsory. At a★ = 0.95, the ergosphere at the equator extends to 1.63 rg vs the event horizon at 1.31 rg. The reconnection layer forms at the ergosphere boundary itself, driven by the differential rotation of field lines. At a★ = 0.7, the ergosphere shrinks to ≈1.86 rg and the event horizon sits at 1.71 rg — a much thinner ergospheric shell, with correspondingly weaker differential rotation. The geometry of the ergosphere is the first variable in the energy budget.

Open Kerr Geometry Viewer → a=0.95 · M = 8,200 M⊙ GR exact
Step payoff
The ergosphere extent and the gap between horizon and ergosphere set the physical volume available to both extraction channels. A thicker ergosphere means more room for reconnection.
02
Step 2 · BZ Jet Power
The Blandford-Znajek Baseline

The BZ mechanism extracts rotational energy via the interaction of magnetic field lines threading the horizon with the frame-dragging of the Kerr spacetime. The split-monopole power is P_BZ = (κ/4πμ0) B² r+4 ΩH² / c with κ ≈ 0.044, which reduces to P_BZ ∝ a★² r+² B². At a★ = 0.95 and B = 106 T: P_BZ ≈ 4.8×1037 W (Scenario A). At a★ = 0.7: P_BZ ≈ 4.4×1037 W (Scenario B). This is the baseline all other channels are compared against, and the BZ term dominates at every spin value here. The two scenarios differ by only 8%, because the horizon radius r+ shrinks as spin rises and largely cancels the a★² growth. The same cancellation makes P_BZ peak near a★ ≈ 0.9 and fall again toward a★ → 1.

Open BZ Calculator → mass=8,200 M☉ · spin=0.95 · B=10⁶ T Blandford-Znajek 1977
Step payoff
The BZ mechanism provides the dominant power floor, and the reconnection channel is a correction on top of it that reaches roughly a fifth of the BZ figure at near-maximal spin.
03
Step 3 · Reconnection Channel
When Plasmoids Add Power

Meringolo, Camilloni & Rezzolla (2025, ApJL 992, L8) ran GRPIC simulations of Kerr magnetospheres and found that plasmoid instabilities in the ergosphere drive a second extraction channel. The tool implements P_rec = 1.646 ηrec a★² P_BZ. At a★ = 0.95 that adds ~22% of the BZ power (Prec ≈ 1.1×1037 W). At a★ = 0.7 the contribution falls to ~12% (≈ 5.3×1036 W). The reconnection layer is physically distinct from the BZ circuit — it operates at the ergosphere boundary, not the horizon. The reconnection efficiency ηrec is calibrated to GRPIC simulation results at ηrec = 0.15. Reconnection power carries two more powers of spin than the BZ term in this parameterisation (P_rec ∝ a★4 r+² B²), so the reconnection share of the total climbs with spin even where the BZ term itself is flattening.

Open Reconnection Calculator → ηrec = 0.15 · B = 106 T · M = 8,200 M⊙ Meringolo 2025 GRPIC
Step payoff
The reconnection channel is not a rounding error at near-maximal spin. It adds ~22% of the BZ power in Scenario A. Spinning the IMBH from 0.7 to 0.95 doubles the reconnection term (5.3×1036 → 1.1×1037 W) while the BZ baseline moves only 8%.
⚖ Combined Channel Budget

At a★ = 0.95 (Scenario A), the combined BZ + reconnection power is Ptotal ≈ 5.8×1037 W, which on the tool's scale K = log10(P)/10 − 0.6 is Kardashev K ≈ 3.18. Reconnection supplies ~18% of that total. Its steeper spin dependence (Prec ∝ a★4 r+²) means the reconnection share grows with spin, but it grows against a BZ baseline that is already near its own maximum.

Spinning the IMBH from a★ = 0.7 to 0.95 raises the BZ term by 8% and the combined total from 4.9×1037 to 5.8×1037 W, a gain of 18%, worth 0.008 in K. The energy case for pushing past a★ = 0.7 is therefore weak on its own: the last stretch of spin-up buys a fifth more power for a large fraction of the accreted mass, and the reconnection channel supplies most of what it does buy. The stronger arguments for near-maximal spin lie elsewhere, in ISCO efficiency and in the total reservoir of extractable rotational energy.

For the spin-up timeline that quantifies how long Phase 1 takes, see Demo — Spin-Up Economics. For the full MTH energy extraction sequence from capture to Kardashev II, see the BH Energy Budget Workflow.

EPISTEMIC TIERS: Established = peer-reviewed physics within the standard formulation. Debated = active disagreement in the published literature. Theoretical = published framework, awaiting decisive observation.