Collapse of Primordial Gas Clouds and the Formation of Quasar Black Holes

The formation of quasar black holes during the hydrodynamic collapse of protogalactic gas clouds is discussed. The dissipational collapse and long- term dynamical evolution of these systems is analysed using three-dimensional numerical simulations. The calculations focus on the final collapse stages of the inner baryonic component and therefore ignore the presence of dark matter. Two types of initial conditions are considered: uniformly rotating spherical clouds, and irrotational ellipsoidal clouds. In both cases the clouds are initially cold, homogeneous, and not far from rotational support ($T/|W| \approx 0.1$). Although the details of the dynamical evolution depend sensitively on the initial conditions, the qualitative features of the final configurations do not. Most of the gas is found to fragment into small dense clumps, that eventually make up a spheroidal component resembling a galactic bulge. About 5\% of the initial mass remains in the form of a smooth disk of gas supported by rotation in the gravitational potential well of the outer spheroid. If a central seed black hole of mass $\gsim10^6M_\odot$ forms, it can grow by steady accretion from the disk and reach a typical quasar black hole mass $\sim10^8M_\odot$ in less than $5\times 10^8\,$yr. In the absence of a sufficiently massive seed, dynamical instabilities in a strongly self- gravitating inner region of the disk will inhibit steady accretion of gas and may prevent the immediate formation of a quasar.