Doeleman, SheperdWeintroub, JonathanRogers, Alan E. E.Plambeck, RichardFreund, RobertTilanus, Remo P. J.Friberg, PerZiurys, Lucy M.Moran, JamesCorey, BrianYoung, KenSmythe, Daniel L.Titus, MichaelMarrone, Daniel P.Cappallo, Roger J.Bock, Douglas C.-J.Bower, Geoffrey C.Chamberlin, RichardDavis, Gary R.Krichbaum, Thomas P.Lamb, JamesManess, HollyNiell, Arthur E.Roy, AlanStrittmatter, PeterWerthimer, DanielWhitney, Alan R.Woody, David2017-09-202008Doeleman, Sheperd S., Jonathan Weintroub, Alan E. E. Rogers, Richard Plambeck, Robert Freund, Remo P. J. Tilanus, Per Friberg, et al. 2008. “Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre.” Nature 455 (7209) (September 4): 78-80. doi:10.1038/nature07245.0369-3392http://nrs.harvard.edu/urn-3:HUL.InstRepos:33921646The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation. Sagittarius A* (Sgr A*), the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4,000,000 times that of the Sun. A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgr A*, where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have detected intrinsic structure in Sgr A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering. Here we report observations at a wavelength of 1.3 mm that set a size of \(37^{+16}_{-10}\) microarcseconds on the intrinsic diameter of Sgr A*. This is less than the expected apparent size of the event horizon of the presumed black hole, suggesting that the bulk of Sgr A* emission may not be centred on the black hole, but arises in the surrounding accretion flow.en-USJournal Article10.1038/nature07245