Letters to Nature

Nature 419, 694-696 (17 October 2002) | doi:10.1038/nature01121; Received 12 August 2002; Accepted 17 September 2002

A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way

R. Schödel1, T. Ott1, R. Genzel1,2, R. Hofmann1, M. Lehnert1, A. Eckart3, N. Mouawad3, T. Alexander4, M. J. Reid5, R. Lenzen6, M. Hartung6, F. Lacombe7, D. Rouan7, E. Gendron7, G. Rousset8, A.-M. Lagrange9, W. Brandner10, N. Ageorges10, C. Lidman10, A. F. M. Moorwood10, J. Spyromilio10, N. Hubin10 & K. M. Menten11

  1. Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
  2. Department of Physics, University of California, Berkeley, California 94720, USA
  3. I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
  4. The Weizmann Institute of Science, Faculty of Physics, PO Box 26, Rehovot 76100, Israel
  5. Harvard-Smithsonian Center for Astrophysics MS42, 60 Garden St, Cambridge, Massachusetts 02138, USA
  6. Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
  7. Observatoire de Paris - Section de Meudon, 5 Place Jules Janssen, 92195 Meudon Cédex, France
  8. Office National d'Etudes et de Recherches Aerospatiales, BP 72, 92322 Chatillon cédex, France
  9. Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, F-38041 Grenoble cédex 9, France
  10. European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany
  11. Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

Correspondence to: R. Schödel1 Correspondence and requests for materials should be addressed to R.S. (e-mail: Email: rainer@mpe.mpg.de) or R.G. (Email: genzel@mpe.mpg.de).

Many galaxies are thought to have supermassive black holes at their centres1—more than a million times the mass of the Sun. Measurements of stellar velocities2, 3, 4, 5, 6, 7 and the discovery of variable X-ray emission8 have provided strong evidence in favour of such a black hole at the centre of the Milky Way, but have hitherto been unable to rule out conclusively the presence of alternative concentrations of mass. Here we report ten years of high-resolution astrometric imaging that allows us to trace two-thirds of the orbit of the star currently closest to the compact radio source (and massive black-hole candidate) Sagittarius A*. The observations, which include both pericentre and apocentre passages, show that the star is on a bound, highly elliptical keplerian orbit around Sgr A*, with an orbital period of 15.2 years and a pericentre distance of only 17 light hours. The orbit with the best fit to the observations requires a central point mass of (3.7 plusminus 1.5) times 106 solar masses (M circle dot). The data no longer allow for a central mass composed of a dense cluster of dark stellar objects or a ball of massive, degenerate fermions.