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Volume 481 Issue 7379, 5 January 2012

The radio source Sgr A* in Sagittarius is thought to be the site of a supermassive black hole lying at the centre of the Milky Way. A study of stellar orbits has identified an object moving towards Sgr A* at a speed of 1,700 kilometres per second. Its low temperature and spectral properties suggest that it is a dusty cloud of ionized gas, three times the mass of Earth, in the process of falling into the black hole. Models predict that as the cloud gets closer to the black hole, X-ray emissions will become much brighter, and a giant radiation flare may be emitted in a few years if the cloud breaks up and feeds gas into the black hole. On the cover, a hydrodynamical simulation set in the year 2025 shows the tidally disrupted gas cloud interacting with the hot accretion flow. In the background are S-stars for which orbits have been determined. (Simulation by M. Schartmann (MPE) using the PLUTO code.)

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