Master Thesis by Henning Holme Mikkelsen – Niels Bohr Institute - University of Copenhagen

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Master Thesis by Henning Holme Mikkelsen

Modeling Density Profiles in Molecular Cores by Bonnor-Ebert Spheres.

With modern observing techniques it has become possible to map the density profiles of molecular cores both in dark cloud complexes and in isolated Bok globules. These density profiles are remarkably similar: they are relatively flat towards the center and fall off like r-2 at larger distances. There have been many attempts to model these profiles by double power-law models, Plummer-like models, logotropic models, magnetic field dominated models and turbulence dominated models. By far the best fit to the observed profiles are, however, given by the Bonnor-Ebert sphere model. This model describes a pressure-bound self gravitating gas cloud in thermal hydrostatic equilibrium. Amazingly enough the Bonnor-Ebert sphere model seems to is able to model both starless and star forming cores in Bok globules. This indicates that these structures indeed are quasi-stable thermally dominated clouds.

The predictive power of the Bonner-Ebert sphere is not restricted to the density profile. It can also be use to model stable longitudinal oscillations and various instabilities in thermally supported clouds.

Despite possible simplifications of the core physics, the Bonnor-Ebert sphere model remains the best available model for starless cores and the initial stages of star forming cores. Due to its inherent simplicity and clear physical content, it should be considered the ideal starting point for more detailed numerical models of the later stages of core collapse and star forming processes in Bok globules.
Supervisor:  Jens Knude, Niels Bohr Institutet