Taking pictures and making movies of black holes

Black holes are cosmic objects so small and dense, that nothing, not even light can escape their gravitational pull. Until recently, no one had ever seen what a black hole actually looked like. Einstein's theories predict that a distant observer should see a ring of light encircling the black hole, which forms when radiation emitted by infalling hot gas is lensed by the extreme gravity near the event horizon. The Event Horizon Telescope (EHT) is a global array of radio dishes, linked together by a network of atomic clocks to form an Earth-sized virtual telescope that can resolve the nearest supermassive black holes where this ring feature may be measured. On April 10th, 2019, the EHT project reported success: we have imaged a black hole, and have seen the predicted strong gravitational lensing. In 2022, our team again saw this phenomenon towards the supermassive black hole at the center of our Milky Way galaxy. This talk will cover the background of the project, the technique, and the imaging strategies employed. Expansion of the global array to a next-generation EHT, enabling capture of multi-color movies of black holes, will be discussed.