1. July 9, 2006 Waves and Turbulence 1 Disk accretion: origin and development Nikolay Shakura Sternberg Astronomical Institute Moscow, Russia

2. 2July 9, 2006Waves And Turbulence Outlook Introduction and history Basic equations of disk accretion Non-stationary disk accretion equation and its solutions Disk irradiation by hard emission Conclusions

3. 3July 9, 2006Waves And Turbulence Introduction Discovery: June 18, 1962 -- serendipitous discovery of cosmic X-ray sources (B.Rossi, R.Giacconi, H.Gursky, F.Paulini) by rocket experiment to discover X-ray emission from Moon (actually discovered much later in 1990 by ROSAT) June 18, 1962 -- serendipitous discovery of cosmic X-ray sources (B.Rossi, R.Giacconi, H.Gursky, F.Paulini) by rocket experiment to discover X-ray emission from Moon (actually discovered much later in 1990 by ROSAT)

4. 4July 9, 2006Waves And Turbulence Powerful X-ray luminosity (~10 37 - 10 38 erg/s) remained puzzling until UHURU discovery of accreting X-ray binaries Mid-60s, Ed Salpeter and Yakov Zeldovich suggested powerful energy release from accretion onto moving black holes In 1966, academician Ya.B. Zeldovich proposed me to calculate structure and emission spectrum from strong shock that appears near accreting NS surface

5. 5July 9, 2006Waves And Turbulence NS X-ray emission Accreting matter shock Zeldovich, Shakura 1969, Astronomicheskij Zhurnal

6. 6July 9, 2006Waves And Turbulence 1967, A. Hewish, J. Bell et al – discovery of radio pulsars, proved to be single rotating NS (but not accreting!). Interest to accretion was temporarily diminished… End of 60s – myself and Rashid Sunyaev, encouraged by Ya.B.Zeldovich, start to study processes of disk accretion onto compact relativistic objects (NS, BH) in binary systems

7. 7July 9, 2006Waves And Turbulence Shakura N.I. Astron. Zh. 49, 921 (1972) Shakura N.I., Sunyaev R.A. Black holes in Binary systems. Observational Appearance. Astron. Astrophys. 24, 337 (1973)

8. 8July 9, 2006Waves And Turbulence UHURU satellite (12 December, 1970) headed by R.Giacconi – discovery of accreting NS and BH in binary systems as powerful X- ray sources. This discovery opened new era in astronomy.

9. 9July 9, 2006Waves And Turbulence Over last 30 years, big progress was made in observations and theory of accretion disks Presently, accretion disk studies represent a big field in astrophysics, similar to structure and evolution of stars, interstellar medium, etc.

10. 10July 9, 2006Waves And Turbulence Accretion disk theory is based on Cosmic (magneto) hydrodynamics Radiation transfer GR effects near black holes THE MAIN UNSOLVED ISSUE REMAINS ANGULAR MOMENTUM TRANSFER (turbulence? magnetic fields?...)

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19. July 9, 2006Waves and Turbulence19 continuity angular mom. transfer

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21. July 9, 2006Waves and Turbulence21 h F t1t1 t2t2 t3t3 t 3 >t 2 >t 1 t1t1 t3t3 h Self-similar solution Filipov, Lyubarskij, Shakura 1987 Separation variables method Lipunova, Shakura 2000

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36. July 9, 2006Waves and Turbulence36 Results of the modeling of nonstationary disk accretion.

37. July 9, 2006Waves and Turbulence37 Almost all models require 1.5-2 times larger disk thickness than from standard theory to account for observed optical emission due to hard emission reprocessing by the disk. This issue is solved by setting a hot (1-2 mln K) corona above the disk. X-ray emission is effectively scattered by the corona and additionally illuminate the standard disk. Jimenez-Garate et al (2002)

38. July 9, 2006Waves and Turbulence38 Iluminated disk geometry.

39. July 9, 2006Waves and Turbulence39 We solve α-disk vertical structure at given radius using standart system of ordinary differential equations with radiative transfer in diffusion aproximation and inclusion of irradiation term in equation of energy generation. Simplified, but elegant, disk solution with X-ray illumination Vertical disk structure equations:

40. July 9, 2006Waves and Turbulence40 Treatment of radiative transfer in X-rays: Equation of radiative transfer for scattered photons using V.V.Sobolev method (in Eddington approximation) can be reduced to: It’s solution: Therefore, energy generation in the disk produced by X-ray irradiation: x

41. July 9, 2006Waves and Turbulence41 Importance of scatering in corona for disk heating via irradiation standard disk: sinΘ ~ 0.01 disk+corona: sinΘ ~ 0.1 Σ c =0.01 M=1 M sun ; Mdot=10 17 g/s ; r=10 10 cm

42. July 9, 2006Waves and Turbulence42 Influence of irradiation on the disk structure  Disk optical depth τ drops  Mass accretion rate in the zone with irradiation DOES NOT CHANGE  Photospheric thickness of the disk Z ph DOES NOT RISE  Temperature at disk photosphere T phot grows and, for strong irradiation, temperature in central plane of the disk T c also increases  Because of growth of temperature in the central plane T c characteristic time of viscous diffusion can obviously decrease in disks with irradiation see Mescheryakov, Lichachev, Shakura(2006) in prep.  The mass of the disk and surface density Σ in the zone with irradiation decreases