Most of the time, Sagittarius A*, the black hole at the Milky Way’s centre, lies dormant; only occasionally does the black hole emit flares, which originate from matter falling towards the event horizon, heating up and releasing energy. But in 2013 a large gas cloud will come within 40 billion km, or 36 lighthours of the black hole, and is expected to be sucked into it.
The gas cloud was first detected in infrared images in 2002, measures about 250 times the Earth-Sun distance across and has a mass roughly three times that of Earth. Composed mostly of hydrogen and helium, it is travelling at a speed of over 8 million km/h towards the black hole, its speed having doubled over the past seven years.
When it nears the accretion zone of the black hole, which has a mass 4.3 million times that of the Sun, scientists expect to see the cloud ripped apart by the tidal forces that surround it. When this happens, the temperature of the cloud will increase rapidly, from 550°K (280°C) to several million degrees Kelvin. This will result in much higher levels of x-ray emission from the black hole region.
“Detailed observations of the radiation from the Galactic centre over the next years will give us the unique opportunity to probe the properties of the accretion flow and observe the feeding process of a supermassive black hole in real time,” predicts the Max Planck Institute’s Stefan Gillessen, who is lead author of the paper.