Nuclear Disk Formation by Direct Collisions of Gas Clouds with the Central Black Hole

Abstract

We simulate clouds in the Galactic Centre (GC) crossing over the black hole in parts and present this as a possible formation mechanism for the observed stellar disks in the GC through the redistribution of angular momentum by colliding material with opposite angular momentum. A parameter study using six high resolution simulations of an isothermal cloud of constant density falling onto the black hole and crossing over it in parts demonstrates that this mechanism is able to reproduce the observed disk properties in the GC. The evolution of the ensuing accretion disks is highly non-linear with the redistribution of the angular momentum through dissipative processes being a dominant effect. We analyse the resulting Toomre unstable, eccentric gaseous disk and show that this already yields a good comparison with the observed stellar disk size and eccentricity in the GC. The best simulation results in an outer radius of 1 pc, a mass of 10$^4$ M$_{sun}$ and an eccentricity of 0.24 for the Toomre unstable disk, which compares well with the observations.