@article{c6df0c650a0a42a49cb3a2543b11bcdf,
title = "Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre",
abstract = "The 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 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.",
author = "Doeleman, {Sheperd S.} and Jonathan Weintroub and Rogers, {Alan E.E.} and Richard Plambeck and Robert Freund and Tilanus, {Remo P.J.} and Per Friberg and Ziurys, {Lucy M.} and Moran, {James M.} and Brian Corey and Young, {Ken H.} and Smythe, {Daniel L.} and Michael Titus and Marrone, {Daniel P.} and Cappallo, {Roger J.} and Bock, {Douglas C.J.} and Bower, {Geoffrey C.} and Richard Chamberlin and Davis, {Gary R.} and Krichbaum, {Thomas P.} and James Lamb and Holly Maness and Niell, {Arthur E.} and Alan Roy and Peter Strittmatter and Daniel Werthimer and Whitney, {Alan R.} and David Woody",
note = "Funding Information: Acknowledgements High-frequency VLBI work at MIT Haystack Observatory is supported by grants from the National Science Foundation. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics. We thank G. Weaver for the loan of a frequency reference from Johns Hopkins University Applied Physics Labs; J. Davis for use of GPS equipment; I. Diegel, R. Vessot, D. Phillips and E. Mattison for assistance with hydrogen masers; the NASA Geodesy Program for loan of the CARMA Hydrogen Maser; D. Kubo, J. Test, P. Yamaguchi, G. Reiland, J. Hoge and M. Hodges for technical assistance; M. Gurwell for SMA calibration data; A. Kerr and A. Lichtenberger for contributions at ARO/SMT; A. Broderick, V. Fish, A. Loeb and I. Shapiro for discussions; and the staff at all participating facilities.",
year = "2008",
month = sep,
day = "4",
doi = "10.1038/nature07245",
language = "English (US)",
volume = "455",
pages = "78--80",
journal = "Nature",
issn = "0028-0836",
publisher = "Nature Publishing Group",
number = "7209",
}