The black hole at the centre of the M87 galaxy may be twice as big was previously thought, and could be large enough to measure directly.
M87 is 55 million light years away. Its central black hole devours vast amounts of gas and spews out a huge jet of particles that extends far into intergalactic space.
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Karl Gebhardt at the University of Texas at Austin and Thomas Jens of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, weighed M87 by running existing data through a new model that simulates the galaxy on a supercomputer. Unlike earlier efforts, the model accounts for the invisible halo of dark matter thought to surround the galaxy. Their analysis credited the monstrous central black hole with a mass of 6.4 billion suns - much more than was expected (The Astrophysical Journal, DOI: 10.1088/0004-637X/700/2/1690).
M87's black hole, when viewed from Earth, would be the same apparent size as the nearer black hole at the centre of the Milky Way. This puts M87's hole within reach of radio astronomy techniques that measure a black hole directly, by tracing its dark silhouette against the glow of surrounding gas.