Steady jet ejections from the innermost region of advection-dominated accretion flow around a black hole

Abstract

Abstract We study ejection mechanisms for two kinds of steady jets: one observed from black hole binaries in the low/hard state and the other from SS 433. The specific energy of the ejected gas is required to be positive for the jets to get to infinity, while that of the accreted gas is naively considered to be negative at the outermost boundary of the accretion flow. To reconcile the opposite sign of the specific energies, we propose a situation where two layers exist in the accretion flow and one layer receives energy from the other sufficiently for the specific energy to be positive. For the steady jets in the low/hard state, the accretion ring at the outermost end of the accretion flow is considered to yield two-layer flow in which a geometrically thick advection-dominated accretion flow (ADAF) sandwiches a geometrically thin accretion disk and the thin disk is supposed to change to another ADAF on the inner side. The energy transfer is expected to occur through turbulent mixing between the two layers and the upper layer is discussed as having a positive specific energy large enough for the terminal velocity to be ∼0.1 c. For the steady jets from SS 433, it is argued that a slim disk separates into two stratified layers due to the photon diffusion in the direction perpendicular to the equatorial plane under the advection-dominated situation. In this case, the specific energy of the upper layer is expected to be positive such that the terminal velocity exceeds 0.2c. The jet ejection process near the black hole is investigated commonly to both the two-layer cases and predicts that the jet opening angle becomes as small as 2°.