Black Holes: Visualizing the Void

Since the 18th century, scientists have been intrigued by the notion of a celestial body with gravity so strong that light cannot escape its pull. This concept was given new life in the early 20th century with Einstein’s introduction of his theory of gravity, known as General Relativity. These mysterious objects, named Black Holes in the 1960s, are made visible by virtue of their influence on nearby light and matter. Four years ago the Event Horizon Telescope (EHT) became the first experiment to image – to visualize – a black hole. Last year EHT released a second image, of a different black hole. What do these images show, and what do they mean to physicists? In this talk, Prof. Charles Gammie will describe in qualitative terms how Newton’s theory of gravity differs from Einstein’s, using examples from our own solar system. Then he will describe the origin of the light seen in the EHT images and why the images have a characteristic ringlike structure. Finally, he will describe what physicists learn from these images, and what we can expect from the next generation of black hole imaging experiments.