Recent measurements of stellar orbits1,2,3 provide compelling evidence that the compact radio source Sagittarius A* (refs 4, 5) at the Galactic Centre is a 3.6-million-solar-mass black hole. Sgr A* is remarkably faint in all wavebands other than the radio region6,7, however, which challenges current theories of matter accretion and radiation surrounding black holes8. The black hole's rotation rate is not known, and therefore neither is the structure of space-time around it. Here we report high-resolution infrared observations of Sgr A* that reveal ‘quiescent’ emission and several flares. The infrared emission originates from within a few milliarcseconds of the black hole, and traces very energetic electrons or moderately hot gas within the innermost accretion region. Two flares exhibit a 17-minute quasi-periodic variability. If the periodicity arises from relativistic modulation of orbiting gas, the emission must come from just outside the event horizon, and the black hole must be rotating at about half of the maximum possible rate.
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This Letter is based on observations at the VLT of the European Observatory (ESO) in Chile. We thank the teams who developed and constructed the near-infrared camera CONICA and the AO system NAOS, and especially their principal investigators, R. Lenzen, R. Hofmann and G. Rousset. We thank H. Falcke and S. Markoff for access to their database of the SgrA* SED, as well as discussions of emission processes. We are grateful to D. Porquet and P. Predehl for discussions of their XMM data, S. Nayakshin, M. Rees, R. Sunyaev and especially E. Quataert for discussions of accretion disk physics, and A. Sternberg for suggestions on the paper.
The authors declare that they have no competing financial interests.
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Genzel, R., Schödel, R., Ott, T. et al. Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre. Nature 425, 934–937 (2003) doi:10.1038/nature02065
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