Accretion process around compact objects
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The document discusses accretion processes around compact objects like black holes. It notes that up to 50% of stars exist in binary systems, meaning there may be millions of binary systems containing a black hole. As material spirals inward due to friction, energy is released and the spectrum and luminosity of the outgoing radiation depends on the accretion rate. At subcritical rates, the disk luminosity is around 1034-1036 erg/sec and the maximum temperature reaches 3x105-106 K in the inner disk. The frequency dependence of radiation intensity can be approximated as ν-1/3. Theories of disk accretion at subcritical regimes are discussed, assuming Newtonian mechanics and taking the inner disk boundary to be 3 gravitational
Accretion process around compact objects
- 1. Accretion process around compact objects Ramiz Ahmad
- 2. 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.
- 3. 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!
- 4. 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.
- 6. 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.
- 7. Mechanisms of Angular Momentum transfer 1. Tangential stresses between adjacent layers. 2. Turbulence. 3. Molecular and radiative viscosity.