Andrew Chael

Princeton University, December 1, 12:00 pm

Polarized Images of Black Holes

Extragalactic jets seen throughout the universe transport energy from small scales near a galaxy’s central supermassive black hole to large distances outside the galaxy itself. These jets may be launched via the Blandford-Znajek mechanism, where magnetic fields around extract a black hole’s spin energy. In this talk, I will discuss what polarized Event Horizon Telescope (EHT) images of synchrotron radiation from close to the event horizon of the supermassive black hole M87* tell us about black hole magnetic fields and jet launching. Polarized synchrotron radiation observed by the EHT probes the plasma properties and the structure of magnetic fields near the black hole. In a large library of simulated images from general relativistic magnetohydrodynamic (GRMHD) simulations, the only models consistent with both EHT polarized images and the observed jet power from M87* are magnetically arrested accretion disks, where near-horizon magnetic fields are coherent and dynamically important. Recent work constraining the resolved circular polarization around M87* confirms that the accretion disk is most likely magnetically arrested. The pattern of linear polarization in black hole images directly probes the direction of electromagnetic energy flux; EHT images show that electromagnetic energy flows outward on horizon scales around M87*. Future EHT observations of M87 will be sensitive enough to detect fainter emission both closer to the event horizon and farther downstream in the jet launching region. These observations will enable a definitive test of the Blandford-Znajek mechanism for powering extragalactic jets.