Science: By linking widely separated radio telescopes together, a team of researchers is hoping to resolve a black hole’s event horizon, the boundary beyond which gravity is so strong that light cannot escape. They aren’t there yet, but the team, led by Sheperd Doeleman from MIT’s Haystack Observatory, has been able to measure the size of a high-energy jet emanating from the black hole at the center of galaxy M87. Doeleman says that the measurements match only a single model of jet formation, in which the black hole is rotating and the material orbiting in the accretion disk is swirling in the same direction. The team’s goal is to reach a resolution where they can determine whether Einstein’s general theory of relativity breaks down at black holes’ event horizons.