Measurements of stellar orbits1,2,3 provide compelling evidence4,5 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 flares6,7, Sgr A* is surprisingly faint, suggesting that the accretion rate and radiation efficiency near the event horizon are currently very low3,8. 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.
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Ghez, A. M. et al. Measuring distance and properties of the Milky Way's central supermassive black hole with stellar orbits. Astrophys. J. 689, 1044–1062 (2008)
Gillessen, S. et al. Monitoring stellar orbits around the massive black hole in the Galactic Center. Astrophys. J. 692, 1075–1109 (2009)
Genzel, R., Eisenhauer, F. & Gillessen, S. The Galactic Center massive black hole and nuclear star cluster. Rev. Mod. Phys. 82, 3121–3195 (2010)
Reid, M. J., Menten, K. M., Trippe, S., Ott, T. & Genzel, R. The position of Sagittarius A*. III. Motion of the stellar cusp. Astrophys. J. 659, 378–388 (2007)
Doeleman, S. S. et al. Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre. Nature 455, 78–80 (2008)
Baganoff, F. K. et al. Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre. Nature 413, 45–48 (2001)
Genzel, R. et al. Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre. Nature 425, 934–937 (2003)
Marrone, D. P., Moran, J. M., Zhao, J.-H. & Rao, R. An unambiguous detection of Faraday rotation in Sagittarius A*. Astrophys. J. 654, L57–L60 (2007)
Lenzen, R., Hofmann, R., Bizenberger, P. & Tusche, A. CONICA: the high-resolution near-infrared camera for the ESO VLT. Proc. SPIE (ed. Fowler, A. M.). 3354, 606–614 (1998)
Eisenhauer, F. et al. SINFONI—Integral field spectroscopy at 50 milli-arcsecond resolution with the ESO VLT. Proc. SPIE (eds Iye, M. & Moorwood, A. F. M.). 4841, 1548–1561 (2003)
Bonnet, H. et al. Implementation of MACAO for SINFONI at the Cassegrain focus of VLT, in NGS and LGS modes. Proc. SPIE (ed. Wizinowich, P.). 4839, 329–343 (2003)
Zhao, J. H., Morris, M. M., Goss, W. M. & An, T. Dynamics of ionized gas at the Galactic Center: Very Large Array observations of the three-dimensional velocity field and location of the ionized streams in Sagittarius A West. Astrophys. J. 699, 186–214 (2009)
Martins, F. et al. Stellar and wind properties of massive stars in the central parsec of the Galaxy. Astron. Astrophys. 468, 233–254 (2007)
Scoville, N. Z., Stolovy, S. R., Rieke, M., Christopher, M. & Yusef-Zadeh, F. Hubble Space Telescope Paα and 1.9 micron imaging of Sagittarius A West. Astrophys. J. 594, 294–311 (2003)
Xu, Y.-D., Narayan, R., Quataert, E., Yuan, F. & Baganoff, F. K. Thermal X-ray iron line emission from the Galactic Center black hole Sagittarius A*. Astrophys. J. 640, 319–326 (2006)
Yuan, F., Quataert, E. & Narajan, R. Nonthermal electrons in radiatively inefficient accretion flow models of Sagittarius A*. Astrophys. J. 598, 301–312 (2003)
Klein, R. I., McKee, C. F. & Colella, P. On the hydrodynamic interaction of shock waves with interstellar clouds. 1: Nonradiative shocks in small clouds. Astrophys. J. 420, 213–236 (1994)
Chandrasekhar, S. Hydrodynamic and Hydromagnetic Stability 428–514 (Dover Publications, 1961)
Murray, S. D. &. Lin, D. N. C. Energy dissipation in multiphase infalling clouds in galaxy halos. Astrophys. J. 615, 586–594 (2004)
Cooper, J. L., Bicknell, G. V., Sutherland, R. S. & Bland-Hawthorn, J. Starburst-driven galactic winds: filament formation and emission processes. Astrophys. J. 703, 330–347 (2009)
Baganoff, F. K. et al. Chandra X-ray spectroscopic imaging of Sgr A* and the central parsec of the Galaxy. Astrophys. J. 591, 891–915 (2003)
Sanders, R. H. The circumnuclear material in the Galactic Centre—a clue to the accretion process. Mon. Not. R. Astron. Soc. 294, 35–46 (1998)
Sharma, P. Quataert, E. Hammett, G. W. & Stone, J. M. Electron heating in hot accretion flows. Astrophys. J. 667, 714–723 (2007)
Blandford, R. D. & Begelman, M. C. On the fate of gas accreting at a low rate on to a black hole. Mon. Not. R. Astron. Soc. 303, L1–L5 (1999)
Bartko, H. et al. Evidence for warped disks of young stars in the Galactic Center. Astrophys. J. 697, 1741–1763 (2009)
Martins, F. et al. GCIRS 16SW: a massive eclipsing binary in the Galactic Center. Astrophys. J. 649, L103–L106 (2006)
Ozernoy, L. M., Genzel, R. & Usov, V. V. Colliding winds in the stellar core at the Galactic Centre: some implications. Mon. Not. R. Astron. Soc. 288, 237–244 (1997)
Cuadra, J., Nayakshin, S., Springel, V. & Di Matteo, T. Accretion of cool stellar winds on to Sgr A*: another puzzle of the Galactic Centre? Mon. Not. R. Astron. Soc. 260, L55–L59 (2005)
This paper is based on observations at the Very Large Telescope (VLT) of the European Observatory (ESO) in Chile. We thank C. McKee and R. Klein for discussions on the cloud destruction process. J.C. acknowledges support from FONDAP, FONDECYT, Basal and VRI-PUC. A.B. acknowledges the support of the excellence cluster 'Origin and Structure of the Universe'.
The authors declare no competing financial interests.
About this article
Cite this article
Gillessen, S., Genzel, R., Fritz, T. et al. A gas cloud on its way towards the supermassive black hole at the Galactic Centre. Nature 481, 51–54 (2012). https://doi.org/10.1038/nature10652
Computational Astrophysics and Cosmology (2018)
Nature Astronomy (2017)