A global solution to a slim accretion disk with radiation-driven outflows

TL;DR

This paper derives a global model for slim accretion disks around black holes that includes radiation-driven outflows, revealing critical accretion rates for outflow launching and implications for black hole growth and observable spectra.

Contribution

It presents the first global solution for slim disks with radiation-driven outflows, detailing how outflows depend on accretion rates and impact black hole growth and emission spectra.

Findings

Outflows occur when accretion rate exceeds ~1.78-1.91 times Eddington rate.

Mass accretion rate decreases inward due to outflows, limiting black hole growth.

Outflows cause spectral saturation at high energies, testable by observations.

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). It was found that vertical gravity increases 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 $\dot{m} \gtrsim 1.78-1.91$ ($\dot{m}=\dot{M}/\dot{M}_{\rm Edd}$, and $\dot{M}_{\rm Edd}=L_{\rm Edd}/0.1c^2$) depending on BH mass, while the outflows are suppressed when the mass accretion rate is lower than this critical value. The mass accretion rate decreases with decreasing radius in the disk with outflows, and the rate of the gas swallowed by the BH is always limited to $\dot{m}_{\rm in}\sim 1.78-1.91$ 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.