Abstract

Black holes are theoretical predictions of Einstein’s General Theory of Relativity, where large amounts of matter are concentrated so much that even light cannot escape its gravitational attraction. Thus, black holes mark singularities in space and time, which are surrounded by an event horizon that allows matter and light to go inwards but never go out again. However, do these supermassive black holes and their event horizons really exist? The best place to test this is the centre of our own Milky Way. Here a compact radio source with a mass of 4 million times the mass of the sun seems to mark the central black hole of our galaxy, providing by far the best evidence for existence of black holes in general. Moreover, its high-frequency radio, near-infrared, and X-ray emission seem to come directly from event horizon scales. With the help of advanced numerical general relativistic magneto-hydrodynamic simulations emission and appearance of the source can be successfully modelled almost from first principles. Using global mm-wave Very Long Baseline Interferometry (VLBI) experiments – an “Event Horizon Telescope” – it should be possible to even image the elusive event horizon of a black hole for the very first time. All this we address within the framework of a new ERC -funded project, BlackHoleCam, which seeks to turn Sgr A* into a fundamental laboratory for precision black hole astrophysics.