Is jet power set by black hole spin via Blandford-Znajek?
In plain words
Theory predicts that magnetic fields threading a spinning black hole extract its rotational energy into jets, so faster-spinning holes should have stronger jets.
Precise statement
Test the Blandford-Znajek scaling $P_{\mathrm{jet}} = (\kappa/(4 \pi c)) \Phi_{\mathrm{BH}}^2 \Omega_H^2$ (Gaussian units; $\Phi_{\mathrm{BH}}$ the magnetic flux through the horizon, $\Omega_H$ the horizon angular frequency, $\kappa \sim 0.05$) against measured spins and jet powers in X-ray binaries and AGN. Answer: a demonstrated correlation, or its absence, of jet power with spin at fixed flux and accretion rate, using spins from independent methods.
What would settle it
A sample of black holes with spins measured by two independent methods and jet powers from calorimetry, showing or excluding the predicted $\Omega_{\mathrm{H}}^2$ dependence.
Status in the literature
Proposed spin-jet power correlations in X-ray binaries (2012) were disputed; Event Horizon Telescope polarimetric images of M87* (2021) favor magnetically arrested accretion consistent with spin-powered jets but do not measure spin.