Journal Article

Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre

Chamberlin, Richard, Krichbaum, Thomas P., Cappallo, Roger J., Werthimer, Daniel, Whitney, Alan R., Moran, James M., Niell, Arthur E., Corey, Brian, Smythe, Daniel L., Young, Ken H., Strittmatter, Peter, Plambeck, Richard, Weintroub, Jonathan, Doeleman, Sheperd S., Davis, Gary R., Maness, Holly, Titus, Michael, Rogers, Alan E. E., Ziurys, Lucy M., Tilanus, Remo P. J., Friberg, Per, Marrone, Daniel P., Bock, Douglas C.-J., Woody, David, Lamb, James, Bower, Geoffrey C., Freund, Robert, Roy, Alan

2008

Overview

Black hole physics: A new window on the Galactic Centre Using Very Long Baseline Interferometry (VLBI) at the relatively short radio wavelength of 1.3 mm, a new intrinsic size estimate has been obtained for Sagittarius A*, the supermassive black hole candidate at the centre of the Milky Way. The resulting lower limit on the size of Sgr A* is less than the predicted size of the event horizon of the presumed black hole, suggesting that Sgr A* emissions centre not on the black hole itself but on the surrounding accretion flow. VLBI observations of the Galactic Centre at around 1.3 mm, less influenced by interstellar scattering than those made at longer wavelengths, open a new window onto black-hole physics that will become even more sensitive as new VLBI stations are built. The cores of most large galaxies are thought to harbour super massive black holes. Sagittarius 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. This paper reports observations that set a limit 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. 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 1 . 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 2 , 3 . 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 4 , 5 , 6 , 7 . 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.

• Publisher: Nature Publishing Group UK,Nature Publishing,Nature Publishing Group
• Subject: Accretion / Astronomical instruments / Astronomy / Astrophysics / Black holes / Black holes (Astronomy) / Characteristics and properties of the milky way / Earth, ocean, space / Emission / Emissions / Exact sciences and technology / Galactic center, bar, circumnuclear matter, and bulge (including black hole and distance measurements) / Galaxies / Harbours / Humanities and Social Sciences / letter / multidisciplinary / Nuclear power generation / Scattering / Science / Science (multidisciplinary) / Spatial resolution / Stars & galaxies / Stellar systems. Galactic and extragalactic objects and systems. The universe / Wavelengths / X-ray spectroscopy