| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1996: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1995: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1994: ¥900,000 (Direct Cost: ¥900,000)
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| Research Abstract |
The effects of radiation force by the cosmic background radiation (CBR) on early-formed objects shortly after the cosmological recombination have been explored. The radiation force by the CBR is calculated by solving radiative transfer equation with including Thomson scattering, under an assumption that a disk is locally approximated to be a plane-parallel medium in longitudinal motion. The results show that the efficiency of angular momentum extraction by the CBR decreases exponentially with optical depth even if the radiative diffusion is effective. Bacause of the present effects, the distributions of the spin probability of early-formed disks could be significantly modified in the presence of the strong CBR.Also, the CBR force likely helps to enhance the effects of shear viscosity, thereby enabling a seed black hole form at z>10 to account for quasar formation.
Also, we have examined the possibility that a population of relic massive black holes, perhaps constituting an important com
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ponent of the dark matter, might be indirectly detected via their occasional very strong gravitational lensing of individual luminous stars in distant external galaxies. For plausible, and in some respects conservative, values of the relevant physical parameters, we show that such events might be detected either in wide area surveys reaching routine CCD magnitude limits (such as the Sloan Digital Sky Survey) or in small field, very deep images (such as the HDF). Thus, it would be a challenging but not impossible task to detect or place limits on a cosmic population of relic massive black holes.
Furthermore, we have proposed a novel mechanism for fuelling active galactic nuclei (AGNs), i.e., a radiative avalanche, which is mass-accretion driven by radiation drag exerted by stellar radiation from circumnuclear starburst regions. If a surface layr of a rotating gas disk is irradiated by intensive starlight, then it could lose angular momentum via radiation drag, resulting in an avalanche of the layr as an inevitable consequence. Analyzes show that in an optically thick regime, the mass-accretion rate via this radiative avalanche is in dependent of not only the extinction coefficient of photon absorbing matter but also the density distribution of the disk, and the maximal mass-accretion rate is simply described as M-L_m/c^2 with L_m being the bolometric luminosity of a starburst. In the present context, the intensity of radiative avalanche determines whether a starburst galaxy is destined to posses an AGN or not. The present model provides a solid physical mechanism deduced from first principles to account for the possible link between starburst activities and AGNs, which has been suggested by a number of observations. Less
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