Computer Science – Numerical Analysis
Scientific paper
Feb 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994pasj...46...87f&link_type=abstract
PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264), vol. 46, no. 1, p. 87-95
Computer Science
Numerical Analysis
18
Accretion Disks, Black Holes (Astronomy), Cosmology, Dark Matter, Drag, Gravitational Fields, Radiation Effects, Universe, Active Galactic Nuclei, Gas Pressure, Numerical Analysis, Point Sources, Subsonic Flow, Supersonic Flow, Transonic Flow
Scientific paper
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 that the 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 Vr is expressed as Vr = -beta r far from the center and as Vr = 2 beta r near the center, where r is the distance from the center, while the rotation velocity Vphi is constant far from the center and almost Keplerian (i.e., Vphi = square root of (GM/r)) 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((omegaDM)2) (omegaDM = const.), we find steady analytical solutions in the cold regime such that Vr = -(beta/2)r and Vphi = r(square root of (((omegaDM)2) - ((beta2)/4))). 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. Shortly after 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 drag with 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.
Fukue Jun
Umemura Masayuki
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