Eccentric disc instability in stellar discs formed from inspiralling gas clouds in the Galactic Centre

Abstract

The inspiral of a turbulent molecular cloud in the Galactic Centre may result in the formation of a small, dense and moderately eccentric gas disc around the supermassive black hole (SMBH). Such a disc is unstable to fragmentation and may lead to the formation of young massive stars in the central parsec of the Galaxy. Here we perform high-accuracy direct summation N-body simulations of a ring of massive stars (with initial semi-major axes 0.1 < a/pc < 0.4 and eccentricities 0.2 < e < 0.4), subject to the potential of the SMBH, a stellar cusp, and the parent gas disc, to study how the orbital elements of the ring evolve in time. The initial conditions for the stellar ring are drawn from the results of previous simulations of molecular cloud infall and disruption in the SMBH potential. While semi-major axes do not evolve significantly, the distribution of eccentricities spreads out very fast (~1 Myr) as a consequence of cusp precession. In particular, stellar orbits with initial eccentricity e>0.3 (e<0.3) tend to become even more (less) eccentric, resulting in a bimodal eccentricity distribution. The distribution is qualitatively consistent with that of the massive stars observed in the Galactic Centre's clockwise disc.