Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre (original) (raw)

Nature volume 455, pages 78–80 (2008)Cite this article

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 radiation1. 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 Sun2,3. 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 scattering4,5,6,7. 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.

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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.

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Authors and Affiliations

  1. Massachusetts Institute of Technology (MIT) Haystack Observatory, Off Route 40, Westford, Massachusetts 01886, USA ,
    Sheperd S. Doeleman, Alan E. E. Rogers, Brian Corey, Daniel L. Smythe, Michael Titus, Roger J. Cappallo, Arthur E. Niell & Alan R. Whitney
  2. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA ,
    Jonathan Weintroub, James M. Moran & Ken H. Young
  3. Department of Astronomy, University of California Berkeley, 601 Campbell, Berkeley, California 94720-3411 USA,
    Richard Plambeck, Geoffrey C. Bower & Holly Maness
  4. Arizona Radio Observatory, Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson Arizona 85721-0065, USA ,
    Robert Freund, Lucy M. Ziurys & Peter Strittmatter
  5. James Clerk Maxwell Telescope, Joint Astronomy Centre, 660 North A’ohoku Place University Park, Hilo, Hawaii 96720, USA ,
    Remo P. J. Tilanus, Per Friberg & Gary R. Davis
  6. Netherlands Organization for Scientific Research, Laan van Nieuw Oost-Indie 300, NL2509 AC The Hague, The Netherlands ,
    Remo P. J. Tilanus
  7. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, Virginia 22903-2475, USA ,
    Daniel P. Marrone
  8. Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, Illinois 60637, USA ,
    Daniel P. Marrone
  9. CARMA, PO Box 968, Big Pine, California 93513-0968, USA ,
    Douglas C.-J. Bock
  10. Caltech Submillimeter Observatory, 111 Nowelo Street, Hilo, Hawai’i 96720, USA ,
    Richard Chamberlin
  11. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany ,
    Thomas P. Krichbaum & Alan Roy
  12. OVRO, California Institute of Technology, 100 Leighton Lane, Big Pine, California 93513-0968, USA ,
    James Lamb & David Woody
  13. University of California Berkeley, Space Sciences Laboratory, Berkeley, California 94720-7450, USA ,
    Daniel Werthimer

Authors

  1. Sheperd S. Doeleman
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  2. Jonathan Weintroub
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  3. Alan E. E. Rogers
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  4. Richard Plambeck
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  5. Robert Freund
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  6. Remo P. J. Tilanus
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  7. Per Friberg
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  8. Lucy M. Ziurys
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  9. James M. Moran
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  10. Brian Corey
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  11. Ken H. Young
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  12. Daniel L. Smythe
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  13. Michael Titus
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  14. Daniel P. Marrone
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  15. Roger J. Cappallo
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  16. Douglas C.-J. Bock
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  17. Geoffrey C. Bower
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  18. Richard Chamberlin
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  19. Gary R. Davis
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  20. Thomas P. Krichbaum
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  21. James Lamb
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  22. Holly Maness
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  23. Arthur E. Niell
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  24. Alan Roy
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  25. Peter Strittmatter
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  26. Daniel Werthimer
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  27. Alan R. Whitney
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  28. David Woody
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Corresponding author

Correspondence toSheperd S. Doeleman.

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Doeleman, S., Weintroub, J., Rogers, A. et al. Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre.Nature 455, 78–80 (2008). https://doi.org/10.1038/nature07245

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Editorial Summary

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.

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