Cosmological Accretion Disks via External Radiation Drag
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概要
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Accretion disks as well as disk accretion driven by external radiation drag are presented under a steady approximation in the cases of the point-mass potential and of the dark-matter potential. We assume thatthe external drag force can be expressed as -beta_v, where (beta) is a constant coefficient and v the velocity vector.When the gravitational potential is given by a central point-mass M, we find, in a cold regime where the pressure force is neglected, steady solutions such that the infalling velocity v_r is expressed as v_r = -(beta)_r far from the center and as v_r = -2(beta)r near the center, where r is the distance from the center, while therotation velocity is constant far from the center and almost Keplerian (i.e., = ) near the center. In a warm regime, where the effect of the gas pressure is taken into account, a transonic solution is found, where the flow accretes supersonically far from the center, passes a sonic point, and eventually becomes subsonic, but rotating in a nearly Keplerian orbit. When the dark matter exerts a gravitational force, which is assumed to be -r _{DM} ( _{DM} = const.), we find steady analytical solutions in the cold regime such that V_r = -(beta/2)r and V = rJObM - . The effect of the gas pressure is also discussed. Such accretion disks, where the angular momentum is removed via an external radiative drag proportional to the velocity (beta disk), are possible in the post-recombination epoch during the early universe. Shortlyafter the cosmological recombination era, when the radiation density of the cosmic background radiation (CBR) was sufficiently high, the gas could lose its angular momentum efficiently through Compton dragwith the CBR and, consequently, form cosmological accretion disks which evolve into primordial active galactic nuclei (proto-quasars). In a dark matter-dominated universe, the disk gas would initially accrete in the dark-matter potential, eventually forming a central black hole with effectively point-mass potential.
- Astronomical Society of Japanの論文
- 1994-02-00
著者
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梅村 雅之
Univ. Tsukuba Ibaraki
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Umemura Masayuki
台湾
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UMEMURA Masayuki
Department of Physics, Hokkaido University
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