The two largest black holes on the sky are in Sgr A* (at the center of our Galaxy) and in the center of galaxy M87. Recent observations have demonstrated that the apparent size of their horizons, tens of micro-arcseconds on the sky, can be resolved by Very Long Baseline Interferometry (VLBI) at sub-millimeter wavelengths. Imaging the silhouette of these black holes with existing technology opens a new window for probing general relativity, accretion flow physics, and the launching sites of relativistic outflows. This project will study in detail these silhouettes against the background illumination by surrounding gas. The primary goals are to examine the sensitivity of features in the image to details of the accretion flow and of the jet physics, and to separate features which provide generic tests of general relativity. The simulations will use a general-relativistic code which incorporates ray-tracing, gas dynamics, and the relevant plasma physics. The second phase will examine how future observations could resolve the predicted images, in order to optimize the observing strategy and get the most scientific output from a given observing time.
Testing General Relativity in the strong field limit is of great importance for fundamental physics, and black holes have long been known to attract a lot of interest from the general public. The black hole silhouette images from this work will be freely available to everyone via museums and the popular media through popular-level articles and movies.
