Physics
Scientific paper
Apr 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phr...311..463c&link_type=abstract
Physics Reports, Vol. 311, No. 3 - 5, p. 463 - 474
Physics
2
Quasars: Accretion, Black Holes: Accretion Disks
Scientific paper
There are strong observational evidences for metallicities larger than solar in the central few parsecs of quasars up to z > 4. This enriched material is flowing out of the central regions with a high velocity. The author proposes that the enrichment and the outflows are produced in the accretion disk fueling the black hole, in an "intermediate" region between 0.01 and 10 pc, where the disk is locally but not globally gravitationally unstable. Star formation is likely to occur in this part of the disk, which is dense and stays molecular in spite of central irradiation. The newly formed stars accrete gas at a high rate and evolve towards the stage of supernovae. A self-regulated accretion disk made of stars and gas, where the gas is marginally unstable and where the transport of angular momentum is provided by supernovae, is then shown to be a possible solution for the intermediate region. It works for small forming black holes and for powerful quasars accreting near their critical rate, whether the abundances are primordial or not. A large fraction of the supernova shells break out of the disk, and the overabundant gas flows out of the nuclear region, enriching in heavy elements the forming host galaxy and the intergalactic medium. The author proposes that this could be the starting point of heavy element formation in the Universe. Provided that black holes form earlier than stars, this process could explain the abundances observed in the oldest stars of the Galactic halo and in the intergalactic medium at high z, and it could also trigger starbursts in massive galaxies.
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