Bondi/Hoyle and Shakura/Sunyaev - Max-Planck-Institut für ...

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Opacity and scattering • To determine the transport of photons from the center to the disk surface, we need to (approximately) include absorption and scattering • The dominant absorption process is thermal free-free absorption: ¯κabs ∝ ρ T −7/2 • The dominant scattering process is Thomson scattering: ¯κscatt ∝ 1 • The total mean opacity is then 1 ¯κ(ρ, T ) = 1 ¯κabs + ¯κscatt ≈ 1 ¯κabs + 1 ¯κscatt • The last approximation is valid because for any r only one process, free-free absorption or Thomson scattering, is assumed to be important 25
Radiative transport • Transport from center to surface depends on the optical thickness: τ = h 0 ¯κ ρ dz • For an r with τ < 1 the disk is optically thin; then most photons escape freely, the flux is a sum over the local emissivity Λ: F (r) ≈ Λ h • For an r with τ ≥ 1 the disk is optically thick; then photons will scatter and be transported by diffusion. The flux on the surface is approximately given by 4 acT F (r) ≈ τ 26
Page 1 and 2: Accretion: Bondi/Hoyle and Shakura/
Page 3 and 4: Literature • This talk is based o
Page 5 and 6: Accretion onto compact objects •
Page 7 and 8: Models of accretion • Analytical
Page 9 and 10: 2. Spherical accretion 8
Page 11 and 12: Flow description • 1D radial flow
Page 13 and 14: • u(r) at small radii: free-fall
Page 15 and 16: 3. Disk accretion 14
Page 17 and 18: Disk accretion: General features
Page 19 and 20: Sketch of a thin accretion disk 18
Page 21 and 22: Angular momentum conservation • M
Page 23 and 24: Vertical momentum conservation •
Page 25: Viscosity law • Several physical
Page 29 and 30: Structure of the solution • The s
Page 31 and 32: 4. General relativistic torus accre
Page 33 and 34: The torus (thick disk) model • As
Page 35: Summary • Accretion is inflow of

Bondi/Hoyle and Shakura/Sunyaev - Max-Planck-Institut für ...

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