A gas cloud on its way towards the supermassive black hole at the Galactic Centre

• Published in: Nature (London) 2012-01, Vol.481 (7379), p.51-54
• Main Authors: Gillessen, S., Genzel, R., Fritz, T. K., Quataert, E., Alig, C., Burkert, A., Cuadra, J., Eisenhauer, F., Pfuhl, O., Dodds-Eden, K., Gammie, C. F., Ott, T.
• Format: Article
• Language: English
• Subjects: 639/33/34/863; Accretion; Astronomy; Astrophysics; Black holes; Black holes (Astronomy); Characteristics and properties of the milky way; Earth, ocean, space; Exact sciences and technology; Galactic center, bar, circumnuclear matter, and bulge (including black hole and distance measurements); Humanities and Social Sciences; Interstellar gas; letter; multidisciplinary; Natural history; Properties; Science; Science (multidisciplinary); Stars & galaxies; Stellar systems. Galactic and extragalactic objects and systems. The universe; Temperature
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature10652

A gas cloud three times the mass of Earth is observed falling towards Sagittarius A*, the supermassive black hole at the centre of our Galaxy. The attractions of the Galactic Centre 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. Measurements of stellar orbits 1 , 2 , 3 provide compelling evidence 4 , 5 that the compact radio source Sagittarius A* at the Galactic Centre is a black hole four million times the mass of the Sun. With the exception of modest X-ray and infrared flares 6 , 7 , Sgr A* is surprisingly faint, suggesting that the accretion rate and radiation efficiency near the event horizon are currently very low 3 , 8 . Here we report the presence of a dense gas cloud approximately three times the mass of Earth that is falling into the accretion zone of Sgr A*. Our observations tightly constrain the cloud’s orbit to be highly eccentric, with an innermost radius of approach of only ∼3,100 times the event horizon that will be reached in 2013. Over the past three years the cloud has begun to disrupt, probably mainly through tidal shearing arising from the black hole’s gravitational force. The cloud’s dynamic evolution and radiation in the next few years will probe the properties of the accretion flow and the feeding processes of the supermassive black hole. The kilo-electronvolt X-ray emission of Sgr A* may brighten significantly when the cloud reaches pericentre. There may also be a giant radiation flare several years from now if the cloud breaks up and its fragments feed gas into the central accretion zone.