Journal Article

Pseudo-viscous modelling of self-gravitating discs and the formation of low mass ratio binaries

C. J. Clarke

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 396, issue 2, pages 1066-1074
Published in print June 2009 | ISSN: 0035-8711
Published online June 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14774.x
Pseudo-viscous modelling of self-gravitating discs and the formation of low mass ratio binaries

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We present analytic models for the local structure of self-regulated self-gravitating accretion discs that are subject to realistic cooling. Such an approach can be used to predict the secular evolution of self-gravitating discs (which can usefully be compared with future radiation hydrodynamical simulations) and to define various physical regimes as a function of radius and equivalent steady state accretion rate. We show that fragmentation is inevitable, given realistic rates of infall into the disc, once the disc extends to radii >70 au (in the case of a solar mass central object). Owing to the outward redistribution of disc material by gravitational torques, we also predict fragmentation at >70 au even in the case of low angular momentum cores which initially collapse to a much smaller radius. We point out that 70 au is close to the median binary separation and propose that such delayed fragmentation, at the point that the disc expands to >70 au, ensures the creation of low mass ratio companions that can avoid substantial further growth and consequent evolution towards unit mass ratio. We thus propose this as a promising mechanism for producing low mass ratio binaries, which, while abundant observationally, are severely underproduced in hydrodynamical models.

Keywords: accretion, accretion discs; circumstellar matter

Journal Article.  7796 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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