Institute for Advanced Study Astrophysics Seminar

Spatially resolved polarimetric images of black holes with the Event Horizon Telescope (EHT) favor models with strong magnetic fields, so-called Magnetically Arrested Disks or MAD models.  MADs can produce efficient jets via the Blandford-Znajek (BZ) mechanism, which extracts the spin-energy of the black hole.  First, using general relativistic radiative magnetohydrodynamics (GRRMHD) simulations, we develop new "sub-grid" formulae for BZ jet feedback and spin evolution, appropriate for both semi-analytic models and cosmological simulations, for arbitrary spins and accretion rates.  Then, we implement these formulae in the semi-analytic model Serotina, which evolves a cosmological population of supermassive black holes from the seeding epoch (z~20) to the present day.  We demonstrate that spin-down in a MAD universe due to BZ jets has an observable effect moderating SMBH spins across cosmic time.  Forward-modeling selection effects, we make predictions for spin measurements via X-ray reflection spectroscopy, extensions to the EHT via the next-generation EHT (ngEHT) project and Black Hole Explorer (BHEX), and the Laser Interferometer Space Antenna (LISA).  We will discuss upcoming observational tests of magnetized accretion that will be made possible with higher dynamic range and higher resolution imaging, multi-frequency information, and time-domain science.