%0 Journal Article %J ApJL %D 2019 %T First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole %A The EHT Collaboration et al. %B ApJL %V 875 %P 4 %G eng %U https://iopscience.iop.org/article/10.3847/2041-8213/ab0e85