Luminous hot accretion discs |
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| Authors: | Feng Yuan † |
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| Institution: | Department of Astronomy, Nanjing University, Nanjing 210093, China; CAS-PKU Joint Beijing Astrophysical Centre, Beijing 100871, China |
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| Abstract: | We find a new two-temperature hot branch of equilibrium solutions for stationary accretion discs around black holes. In units of Eddington accretion rate defined as 10 L Edd c 2, the accretion rates to which these solutions correspond are within the range ? 1? ? ?1, where ? 1 is the critical rate of advection-dominated accretion flow (ADAF). In these solutions, the energy loss rate of the ions by Coulomb energy transfer between the ions and electrons is larger than the viscously heating rate and it is the advective heating together with the viscous dissipation that balances the Coulomb cooling of ions. When ? 1? ? ? ? 2, where ? 2～5 ? 1<1, the accretion flow remains hot throughout the disc. When ? 2? ? ?1, Coulomb interaction will cool the inner region of the disc within a certain radius ( r tr～several tens of Schwarzschild radii or larger depending on the accretion rate and the outer boundary condition) and the disc will collapse on to the equatorial plane and form an optically thick cold annulus. Compared with ADAF, these hot solutions are much more luminous because of the high accretion rate and efficiency; therefore, we call them luminous hot accretion discs. |
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| Keywords: | accretion accretion discs black hole physics hydrodynamics radiation mechanisms: thermal galaxies: active galaxies: nuclei |
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