A Global Solution to a Slim Accretion Disk with Radiation-driven Outflows

Abstract

Abstract The thickness of a slim disk is determined by the balance between the radiation force and the vertical component of the gravity of the black hole (BH). Vertical gravity is found to increase with the disk height, and it will decrease with the disk height if the disk thickness is above a critical value, which implies that gas at the disk surface may be driven into outflows by radiation force when the disk thickness surpasses the critical value. In this work, we derive a global solution to a slim disk with radiation-driven outflows. We find that the outflows are driven from the disk surface if the mass accretion rate is m ˙ ≳ 1.78 − 1.91 ( m ˙ = M ˙ / M ˙ Edd and M ˙ Edd = L Edd / 0.1 c 2 ) depending on the BH mass, while the outflows are suppressed when the mass accretion rate is lower than this critical value. The mass accretion rate decreases with the decreasing radius in the disk with outflows, and the rate of the gas swallowed by the BH is always limited to m ˙ in ∼ 1.78 − 1.91 even if the mass accretion rate at the outer edge of the disk is very high. This may set constraints on the massive BH growth through accretion in the early universe. Due to the presence of outflows, there is an upper limit on the radiation flux of the disk, which leads to saturation of the continuum spectra of the disk with outflows at the high-energy band. This may be tested by the observations of quasars or/and BH X-ray binaries.