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Blobrana


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Giant 'quasi-stars' spawned early black holes

Monstrous black holes in the early universe could have formed deep within giant star-like objects. The most detailed models yet of this scenario could help explain how black holes with a mass of a billion or more suns were created in the first billion years of the universe.
It had been suggested that when a massive gas cloud collapses under gravity, it could form a small black hole at its core, giving rise to an object called a quasi-star. Calculations published in 2006 by Mitchell Begelman of the University of Colorado in Boulder suggested that such a black hole could quickly grow to 1000 times the sun's mass by feeding on the gas shrouding it. Further slow but steady growth would eventually turn it into a supermassive black hole.



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Blobrana


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Title: The Structure and Evolution of Quasi-stars
Authors: Warrick H. Ball (1), Christopher A. Tout (1), Anna N. Zytkow (1), John J. Eldridge (1) ((1) Institute of Astronomy, University of Cambridge)

The existence of bright quasars at high redshifts implies that supermassive black holes were able to form in the early Universe. Though a number of mechanisms to achieve this have been proposed, none yet stands out. A recent suggestion is the formation of quasi-stars, initially stellar-mass black holes accreting from hydrostatic giant-like envelopes of gas, formed from the monolithic collapse of pre-galactic gas clouds. In this work, we modify the Cambridge STARS stellar evolution package to construct detailed models of the evolution of these objects. We find that, in all of our models, the black hole inside the envelope is able to reach slightly more than one-tenth of the total mass of the system before hydrostatic equilibrium breaks down. This breakdown occurs after a few million years of evolution. We show that the mechanism which causes the hydrostatic evolution to end is present in polytropic models. We also show that the solutions are highly sensitive to the size of the inner boundary radius and that no physical solutions exist if the inner boundary is chosen to be less than about 0.3 of the Bondi radius.

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