CRA seminar (Dr. Kohei Inayoshi)

Title: Hyper-Eddington accretion flows onto massive black holes

Abstract: How fast can black holes (BHs) grow?  The existence of bright quasars at high-redshift provides a challenging puzzle about the origin of supermassive BHs. To form such massive objects within a billion year, rapid growth of seed BHs is required. We study very-high rate, accretion flows onto massive BHs embedded in dense metal-poor clouds. In spherically symmetric cases, we find solutions from outside the Bondi radius at hyper-Eddington rates, unimpeded by radiation feedback. Accretion rates in this regime are steady, and larger than 5000 L_Edd/c^2. At lower rates, the accretion is episodic due to radiative feedback and the average rate is below the Eddington rate. The hyper-Eddington accretion solution is maintained as long as the emergent luminosity is limited to < (10-30) L_Edd because of photon trapping due to electron scattering. Furthermore, we perform two-dimensional simulations and find that the transition to a hyper-Eddington accretion phase occur. We apply our result to the rapid formation of massive BHs in protogalaxies. Once a seed BH forms at the center of the galaxy, it can grow to a maximum ~ 10^5 Msun via gas accretion independent of the initial BH mass.