Two‐dimensional adiabatic flows on to a black hole – I. Fluid accretion

By R. Blandford, M. Begelman. 2003

152 citations recorded by the source corpus.

When gas accretes on to a black hole, at a rate either much less than or much greater than the Eddington rate, it is likely to do so in an ‘adiabatic’ or radiatively inefficient manner. Under fluid (as opposed to magnetohydrodynamic) conditions, the disc should become convective and evolve toward a state of marginal instability. We model the resulting disc structure as ‘gyrentropic’, with convection proceeding along common surfaces of constant angular momentum, Bernouilli function and entropy, called ‘gyrentropes’. We present a family of two-dimensional, self-similar models that describes the time-averaged disc structure. We then suppose that there is a self-similar, Newtonian torque, which dominates the angular momentum transport and that the Prandtl number is large so that convection dominates the heat transport. The torque drives inflow and meridional circulation and the resulting flow is computed. Convective transport will become ineffectual near the disc surface. It is conjectured that this will lead to a large increase of entropy across a ‘thermal front’, which we identify as the effective disc surface and the base of an outflow. The conservation of mass, momentum and energy across this thermal front permits a matching of the disc models to self-similar outflow solutions. We then demonstrate that self-similar disc solutions can be matched smoothly on to relativistic flows at small radius and thin discs at large radius. This model of adiabatic accretion is contrasted with some alternative models that have been discussed recently. The disc models developed in this paper should be useful for interpreting numerical, fluid dynamical simulations. Related principles to those described here may govern the behaviour of astrophysically relevant, magnetohydrodynamic disc models.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/14e1a558274fdf1bf71a5c9f2e9af95f4b8cf3b3

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In Astronomy and Astrophysics

1. Ramesh Narayan
2. M. Volonteri
3. F. Yuan
4. A. Sa̧dowski
5. G. Ghisellini
6. F. Tavecchio
7. De-Fu Bu
8. M. Begelman

In Nuclear and High Energy Physics

1. Ramesh Narayan
2. F. Yuan
3. G. Ghisellini
4. F. Tavecchio
5. A. Sa̧dowski
6. M. Begelman
7. M. Volonteri
8. De-Fu Bu

Citations in the corpus

• The blazar sequence: a new perspective (2008, background): “Below this critical values the accretion flow can be advection dominated (Narayan & Yi 1994), or adiabatic inflow–outflow scenario (ADIOS; Blandford & Begelman 1999, 2004), becoming radiatively inefficient, hotter and geometrically thicker.”
• NUMERICAL SIMULATION OF HOT ACCRETION FLOWS. III. REVISITING WIND PROPERTIES USING THE TRAJECTORY APPROACH (2015, background): “In the adiabatic inflow-outflow solution (ADIOS), the inward decrease of mass accretion rate is due to the mass lost in the wind (Blandford & Begelman 1999; 2004; Begelman 2012).”
• Formation of supermassive black holes by direct collapse in pre-galactic haloes (2006, background): “In the absence of a wind that removes energy and/or angular momentum, the accretion rate is reduced to ṀBH ∼ ǫ−1(v∗/c)2Ṁsup (Blandford & Begelman 1999, 2004).”
• Multiband light curves of tidal disruption events (2010, background): “It is not possible to quantify analytically the parameter fout, because the amount of mass that is ejected will depend upon the detailed redistribution of energy and angular momentum within the flow (Blandford & Begelman 2004).”
• Hot Accretion Flows Around Black Holes (2014, background): “solution (ADIOS; Blandford & Begelman 1999, 2004; Begelman 2012), the inward decrease of Ṁin is due to a genuine mass loss in a wind.”