Accretion process around compact objects

Ramiz Ahmad

Plan of the talk:

1. General Picture.

2. Theory of disk accretion at subcritical regime.3. Influence of the hard radiation of the black hole on the outer part of

the disk and visible component.4. Supercritical regime of disk accretion.5. Summary.

The General Picture:1. Up to 50% of the stars are in binary system => No. of binary system

including a black hole may be of the order of 106-108.2. The rate of mass loss depends upon the type of star.3. In binary systems, an additional strong matter outflow connected

with Roch limit surface is possible.4. Consequence of presence of black hole in such binaries!

Because of friction the material looses the energy and spirals in.The total energy released and the spectrum of the outgoing radiation are determined mainly by the rate of accretion.

At subcritical fluxes 10-12-10-10 M0/year the luminosity of the disk is of the order of 1034-1036 erg/sec and the maximal temperature is of the order of TS =3x105-106 K in the inner region of the disk where most of the energy is produced.

For the case of disk accretion there is a weak dependence of the radiation intensity on the frequency which can be given as ν -1- +1/3.

In the case of neutron star without a magnetic field, the disk extends to the surface of the star which gives rise to its own peculiarities.

Theory of disk accretion at subcritical regime :

•All calculations are done using Newtonian mechanics.•In the calculations, it is assumed that L0 = 0.06c2

•The radius R0= 3Rg is taken as the inner boundary of the disk.

Mechanisms of Angular Momentum transfer

1. Tangential stresses between adjacent layers.2. Turbulence.3. Molecular and radiative viscosity.