Horizon-scale images of black hole accretion and jet launching

The Event Horizon Telescope (EHT) has produced images of radiation from relativistic plasma very close to the horizons of two supermassive black holes; in the Galactic Center Sgr A* and M87. In this talk, I will present the past and future of horizon-scale black hole images: how do we get them, what have we learned, and what will they show next? I will first discuss how we reconstruct and validate images from sparse, difficult-to-calibrate EHT data. I will focus on the first polarized images of M87*, which provide the most stringent constraints on a near-horizon environment. Comparing polarized EHT images with a large library of magnetohydrodynamic simulations indicates that the magnetic field near M87* is strong, ordered, and dynamically important in limiting accretion and launching M87's powerful relativistic jet. Finally, I will show how future observations of M87* with an expanded EHT array will have significantly improved dynamic range and resolution. These observations will map the structure and dynamics of plasma and magnetic fields from the central black hole out through the jet on larger scales. They may also reveal substructure in the strongly-lensed image, including the black hole's 'inner shadow.' In the coming decade, new EHT and multiwavelength observations will combine with advances in analysis techniques and simulations to illuminate the black-hole jet connection, probe relativistic plasma microphysics, and enable new tests of spacetime.