Heating or Cooling: Study of Advective Heat Transport in the Inflow and the Outflow of Optically Thin Advection-dominated Accretion Flows

Abstract

Advection is believed to be the dominant cooling mechanism in optically thin advection-dominated accretion flows (ADAF's). When outflow is considered, however, the first impression is that advection should be of opposite sign in the inflow and the outflow, due to the opposite direction of radial motion. Then how is the energy balance achieved simultaneously? We investigate the problem in this paper, analysing the profiles of different components of advection with self-similar solutions of ADAF's in spherical coordinates ($r\theta \varphi$). We find that for $n<3\gamma /2-1$, where $n$ is the density index in $\rho \propto r^{-n}$ and $\gamma$ is the heat capacity ratio, the radial advection is a heating mechanism in the inflow and a cooling mechanism in the outflow. It becomes 0 for $n=3\gamma /2-1$, and turns to a cooling mechanism in the inflow and a heating mechanism in the outflow for $n>3\gamma /2-1$. The energy conservation is only achieved when the latitudinal ($\theta$-direction) advection is considered, which takes an appropriate value to maintain energy balance, so that the overall effect of advection, no matter the parameter choices, is always a cooling mechanism that cancels out the viscous heating everywhere. For the extreme case of $n=3/2$, latitudinal motion stops, viscous heating is balanced solely by radial advection, and no outflow is developed.

9 pages, 4 figures, accepted by ApJ

References in corpus (11)

• Numerical Simulation of Hot Accretion Flows (III): Revisiting wind properties using trajectory approach
• Faraday rotation in the jet of M87 inside the Bondi radius: indication of winds from hot accretion flows confining the relativistic jet
• Mechanism of Outflows in Accretion System: Advective Cooling Cannot Balance Viscous Heating?
• On the structure of Accretion Disks with Outflows
• Numerical simulation of hot accretion flows (IV): effects of black hole spin and magnetic field strength on the wind and the comparison between wind and jet properties
• Evidence for A Hot Wind from High-resolution X-ray Spectroscopic Observation of the Low-luminosity Active Galactic Nucleus in NGC 7213
• Comparison between RHD simulation of supercritical accretion flows and steady model with outflows
• The effects of toroidal magnetic field on the vertical structure of hot accretion flows
• Analytical solution for the structure of ADAFs
• Two-dimensional Inflow-Wind Solution of Hot Accretion Flow. I. Hydrodynamics
• Exact analytical solutions for ADAFs