High-redshift quasar lifetimes exceed 10^4 yr require magnetic pressure up to 100 times gas pressure in accretion disks

The arXiv preprint derives maximum accretion timescales by comparing viscous inflow rates under pure gas-pressure support versus combined gas-plus-magnetic support. Proximity-zone radii measured in high-redshift quasar spectra translate directly into episode durations; the longest observed zones exceed the fragmentation-limited lifetime predicted for gas-pressure-supported disks by an order of magnitude. This forces magnetic pressure to dominate, reaching P_mag/P_gas ratios of ~100 in the inner disk regions. The absence of any zones implying lifetimes definitively above 10^6 yr further indicates that magnetic support does not extend indefinitely, consistent with advection from galactic scales rather than in-situ dynamo amplification.

Standard thin-disk theory assumes vertical support is supplied by gas or radiation pressure; the new constraint implies that magnetic fields must be continuously supplied from the host galaxy to prevent Toomre instability on orbital timescales. This dovetails with earlier analytic work on magnetically arrested disks and with recent GRMHD simulations showing that net vertical flux suppresses fragmentation at Eddington ratios near unity. The pattern suggests that rapid early supermassive-black-hole growth across cosmic time is enabled by the same magnetic advection mechanism, not by exotic super-Eddington episodes alone.

Future ALMA and JWST observations of molecular gas kinematics around additional z>6 quasars will test whether the longest proximity zones correlate with stronger large-scale magnetic-field tracers such as polarized dust emission. If confirmed, the result tightens the requirement that cosmological simulations incorporate realistic galactic-field advection to reproduce the observed quasar luminosity function at early times.