Master's Thesis Defense by Michael Küffmeier – Niels Bohr Institute - University of Copenhagen

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Master's Thesis Defense by Michael Küffmeier

Zooming in on Star Formation and Protoplanetary Disks

In the context of adaptive mesh refinement simulations of the collapse from pre-stellar cores --- simulated as part of giant molecular clouds --- to disks, I investigate in
particular the role of the magnetic field. The initial level of magnetic flux,
at the point in time when the core starts to collapse, is shown to have
important consequences for the size, mass, and structure of the disks.

The magnetic field goes through a characteristic sequence of structure
evolution during the accretion process, starting out with an approximate hour
glass shape in the earliest phases of evolution, then evolving into a structure
that contains a central jet and a broader disk outflow. Late in the accretion
process the magnetic field is mainly oriented along the direction of rotation.
However, non-stationarity, with strong fluctuations in time and space, remain a
characteristic property through the entire process. Jets and outflows, for
example, are seldom symmetric - more often one side or the other dominates,
only to be replaced by the opposite sense of symmetry breaking.

I also investigate the structure of magnetic dissipation in the envelope and
disk, and its possible relation with the occurrence of magnetic null points.
Moreover, the occurrence of magnetic bubbles during the earliest phases of star
formation and their impact on the accretion process is analyzed. At a later
stage of disk evolution, magnetically driven disk clearing is discussed as a
potential explanation for observations of gaps in transition disk. 

The results presented in this thesis give constraints on disk formation, and
show that an adequately large number of cells per level of refinement is
crucial to be able to model the accretion process properly. Insufficient
refinement leads to disks which are lower in mass and more homogeneous, hence
smearing out the influence of turbulence. 

Supervisor: Åke Nordlund