Weighing the cusp at the Galactic Centre

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  • 13 February 2004
Abstract
As stars close to the galactic centre have short orbital periods it has been possible to trace large fractions of their orbits in recent years. Previously the data of the orbit of the star S2 have been fitted with Keplerian orbits corresponding to a 3-4*10^6 M(sun) massive black hole (MBH). However, it has also been shown that the central black hole resides in a ~1'' diameter stellar cluster of a priori unknown mass. In a spherical potential which is neither Keplerian nor harmonic, orbits will precess resulting in rosetta shaped trajectories on the sky. In this case, the assumption of non-Keplerian orbits is a more physical approach. It is also the only approach through which cusp mass information can be obtained via stellar dynamics of the cusp members. This paper presents the first exemplary modelling efforts in this direction. In addition to the solution of a 3.7*10^6 M(sun) black hole with insignificant cusp mass, we obtain best fits for a total (MBH plus cusp) mass of 4.1*10^6 M(sun) with 10% extended component and 4.8*10^6 M(sun) total mass with a 25% extended component. While high total masses above ~5*10^6 M(sun) are in conflict with enclosed mass estimates at larger radii, there is no contradiction for the 10% cusp mass solution which is discussed in detail. It is unlikely that such a high extended mass is composed of sub-solar mass constituents, but could be explained rather well by a cluster of high M/L stellar remnants, which we find to form a stable configuration.

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