Merging between a central massive black hole and a compact stellar system: A clue to the origin of M31's nucleus

The central bulge of M31 is observed to have two distinct brightness peaks with the separation of similar to 2 pc. S. Tremaine recently proposed the new idea that M31's nucleus is actually a single thick eccentric disk surrounding the central supermassive black hole. In order to explore the origin of the proposed eccentric disk, we numerically investigate the dynamical evolution of a merger between a central massive black hole with a mass of similar to 10(7) M. and a compact stellar system with a mass of similar to 10(6) M. and size of a few parsecs in the central 10 pc of a galactic bulge. We find that the stellar system is destroyed by the strong tidal field of the massive black hole and consequently forms a rotating nuclear thick stellar disk. The orbit of each stellar component in the developed disk is rather eccentric with a mean eccentricity of similar to 0.5. These results imply that M31's nuclear eccentric disk proposed by Tremaine can be formed by merging between a central massive black hole and a compact stellar system. We furthermore discuss when and how a compact stellar system is transferred into the nuclear region around a massive black hole.