Journal Article

The Jeans mass as a fundamental measure of self-gravitating disc fragmentation and initial fragment mass

Duncan Forgan and Ken Rice

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 417, issue 3, pages 1928-1937
Published in print November 2011 | ISSN: 0035-8711
Published online October 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19380.x
The Jeans mass as a fundamental measure of self-gravitating disc fragmentation and initial fragment mass

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As a formation route for objects such as giant planets and low-mass stars in protostellar discs (as well as stars in AGN discs), theories of self-gravitating disc fragmentation need to be able to predict the initial masses of fragments. We describe a means by which the local Jeans mass inside the spiral structure of a self-gravitating disc can be estimated. If such a self-gravitating disc satisfies the criteria for disc fragmentation, this estimate provides a lower limit for the initial mass of any fragments formed. We apply this approach to a series of self-gravitating protostellar disc models, to map out the typical masses of fragments produced by this formation mode. We find a minimum fragment mass of around 3MJup, which is insensitive to the stellar mass, and that – within the parameter space surveyed – fragments with masses between 10 and 20 MJup are the most common. We also describe how the Jeans mass allows us to derive a more general criterion for disc fragmentation, which accounts for the processes of viscous heating, radiative cooling, accretion and the disc’s thermal history. We demonstrate how such a criterion can be determined, and show that in limiting cases it recovers several fragmentation criteria that have been posited in the past, including the minimum cooling time/maximum stress criterion.

Keywords: accretion, accretion discs; methods: analytical; planets and satellites: formation; stars: formation

Journal Article.  7434 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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