All eyes are on a cloud of gas, known as G2, that is spiralling towards its doom at the centre of the Milky Way. Discovered in 2011 and with a mass that is three times that of the Earth, G2 is approaching the supermassive black hole, Sagittarius A* — the bright spot in this image from ESA's Herschel space observatory; the blue region shows gas within 10 light-years of the black hole, with hot infalling gas appearing orange. Astronomers first thought the encounter would occur in late 2013, but now estimate the show will begin in early 2014.


Owing to dust obscuring G2 as it moves rapidly away along our line of sight, the exact nature of the cloud remains unclear. If it is indeed a gas cloud, as originally reported, it was probably formed by the collision of stellar winds. However, some evidence suggests it may be an unresolved star. In any case, the onset of tidal shearing, due to gravitational interactions with the tidal field of the black hole, is already measurable.

Although many theories and predictions exist for the fate of G2 (summarized in a preprint by Stefan Gillessen et al.,; 2013), only time will tell. A gas cloud would be completely disrupted by Sagittarius A*, possibly creating a glow for a year or more and/or a large flare; a star, however, could escape unharmed and subsequently reform its gas cover. NASA's Swift space telescope is providing daily updates in the X-ray band, where the most stunning changes will occur.