Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995pasj...47...73t&link_type=abstract
PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264), vol. 47, no. 1, p. 73-79
Astronomy and Astrophysics
Astronomy
8
Cosmology, Deposition, Drag, Galactic Evolution, Galactic Nuclei, Gas Transport, Radiation Effects, Black Holes (Astronomy), Gas Pressure, Gravitational Fields, Mass Transfer, Optical Thickness, Stellar Mass Accretion
Scientific paper
Spherically symmetric non-steady accretion via external radiation drag in the optically thin regime is investigated using self-similar transformations in the gravitational potential by a point-mass M. We assume that the external drag force is proportional to the velocity vector v as -Beta x v, where Beta us spatially constant and is a function of time. In a regime where the effect of gas pressure is not taken into account, we find self-similar solutions which connect the asymptotic solutions such that v = square root of (2GM/r), rho varies as r-3/2t near to the center and v varies as -GMt/r2, rho = const. far from the center. The freefall region spreads with time as rt varies as t2/3. The gas is assumed to be at rest and the density is constant far from the center. It is found that: (1) the drag slows an infalling velocity far from the center, (2) the drag flattens the density distribution near to the center, and (3) the drag decreases the mass-accretion rate. Selecting the radiation drag parameter in order for the ionization degree to be O(1) at an epoch z = 400-200, it is found that this radiation drag reduces the mass accretion rate by a factor of 2. Such spherical accretion via an external radiation drag proportional to the velocities may be realized when the systems are embedded in radiation fields. The present self-similar solution may be applicable for gas accretion into a point-mass potential, which is, for instance, produced by a massive black hole formed during an early epoch.
Fukue Jun
Tsuribe Tohru
Umemura Masayuki
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