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


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 ± 1.5) × 106 solar masses (M). 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.

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Figure 1: Ks-band image of the centre of the Milky Way.
Figure 2: Orbit of S2 around SgrA*.
Figure 3: Mass distribution in the Galactic Centre.


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We thank the teams who developed and constructed the near-infrared camera CONICA and the adaptive optics system NAOS. We are grateful to all the instrument scientists and European Southern Observatory staff involved in the commissioning of NAOS/CONICA for observations of the Galactic Centre. We thank C.H. Townes and J. Kormendy for comments. We thank D. Gudehus for assistance with the Binary-Star Combined Solution Program.

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Schödel, R., Ott, T., Genzel, R. et al. A star in a 15.2-year orbit around the supermassive black hole at the centre of the Milky Way. Nature 419, 694–696 (2002).

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