Radiatively Inefficient Accretion Flows Roman Shcherbakov, 28 November, 2007.

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Presentation transcript:

Radiatively Inefficient Accretion Flows Roman Shcherbakov, 28 November, 2007

Radiative efficiency Innermost Stable Circular Orbit (ISCO) Gas radiates away a lot of its grav. energy efficiency (function of BH spin) ADAF Gas accretes onto the source, but does not radiate due to (1) low density (2) low electron temperature (3) large optical depth efficiency (function of gas density) Radiatively Inefficient Accretion Flows (RIAFs)

Possible RIAF configurations Spherical (Bondi) accretion – dimensionless angular momentum for a typical AGN for Sgr A*The only realistic pattern: every astrophysical system has large angular momentum + outflows

Spherical accretion (Bondi, 1952) radius of influence of BH, 1pc for 10^8M Sun – for u=c S at sonic radius r S, subsonic flow at r>r S, supersonic flow at r>r S Such a solution is (1)Smooth (2)Has maximum accretion rate Physical Efficiency

Not only AGNs, but also Gamma Ray Bursts and protoplanetary disks Thick disk accretion Advection-Dominated Accretion Flow (Narayan, Yi 1995) Adiabatic Inflow-Outflow Solution (Blandford, Begelman 1999) Hawley, Balbus 2002

ADAF luminosity Large optical depth ADAF (ULX sources) Narayan, Mahadevan, Quataert astro-ph/

ADAF/ADIOS/CDAF Advection-Dominated Accretion Flow (Narayan, Yi 1995) Needed to fit the observations Too low electron temperature T e <<T i near the black hole Too Low gas density near the black hole Too small magnetic field in that region ADAF is convectively unstable and does not include diffusion Adiabatic Inflow-Outflow Solution (Blandford, Begelman 1999) ADAF with outflows (Yuan 2001) Convection-Dominated Accretion Flows (Narayan, Igumenshchev, & Abramowicz 2000) Phenomenological inclusion of outflows “The binding energy of a gram of gas at a few gravitational radii drives off 100 kg of gas from gravitational radii” – Blandford Accounts for convective instability of ADAF, but full 3-D analysis is not doable analytically

Spectrum

Jet-ADAF model for Sgr A* Yuan,Markoff, Falcke 2002

Spectral states Hard – X-Rays Soft – UV, IR Narayan, Mahadevan, Quataert astro-ph/

Hawley, Balbus, “The Dynamical Structure of Nonradiative Black Hole Accretion Flows” 2002, ApJ, 573, 738

Hawley, Balbus, “The Dynamical Structure of Nonradiative Black Hole Accretion Flows” 2002, ApJ, 573, 738

Results of Numerical Simulations Hawley, Balbus & Stone, 2001 ApJ, 554, L49 Density Entropy

Time variability At r=4r g Density Temperature

Conclusions Studies are controversial Realistic accretion pattern is likely to be very complicated Numerical simulations are preferable to analytical methods Most effects are not yet included, small resolution MHD instead of plasma calculations Developed in the last 30 years, will we get the ultimate answer within the next 30 years?