Observing the effects of different background media on the critical Bonnor Ebert sphere

This pages describes the effects of placing a marginally stable Bonnor Ebert sphere in different ambient mediums. Two ambient mediums and their effects on BE spheres were measured - a) a uniform light ambient medium (rho=rho(Rbe)/100), and b) an ambient medium with density that matches the density at the sphere's outer edge (rho=rho(Rbe)). The aim was to see if the effect of the "matched" ambient was induced collapse of the sphere, triggered by the ram pressure of the infalling ambient material gravitationally accelerated by the BE sphere. The ram pressure was calculated at the sphere's outer edge and indeed exceeded the critical threshold of external pressure on the BE sphere, resulting in collapse. The sphere in the light ambient medium, however, remained dynamically stable, oscillating slowly about its equilibrium values for ~ 5 crossing times.

Parameters:

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Computational Scales:

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Results:

Note the line marking 'dx' denotes the size of the smallest cells in the grid, those within the BE sphere's center most regions (dx~0.06). The cells outside a radius of 150% Rbe (radius of BE sphere), however, made up the coarsest level grid (see below movies of the mesh) and had dx~1.62 pc for smaller grid and dx~3 for larger grid. The last time frame of data included in these plots and the movies below is the time before the collapse was no longer resolved adequately with the refinement criteria used. Since the aim of this study was to look at the initialization of the collapse, the refinement used here was sufficient. The time in which the sphere collapsed was on the order of 1 crossing time, tsc=3.84 myr.

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The horizontal line in the following plots is the value of Pcrit, where Pcrit~1.14 Cs⁸/G³*M² and characterizes the maximum external pressure a critical BE sphere can withstand before collapsing. Note that both the thermal and ram pressure at the Bonnor Ebert surface, Rbe, is BELOW the threshold under light ambient medium conditions, whereas in the "matched" ambient medium case both of these pressures EXCEED the threshold. (I suppose then that an adequate time to describe the collapse may be when the P>Pcrit?— which is EARLY on according to this data..?).

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Movies Left panel is sphere in the light ambient, right is the matched ambient.

Mesh

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Density

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The BE sphere in the light ambient was stable for 5 crossing times, to see a longer clip see ​here.

Issues - link here

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Discussion

-size differences, computational difficulties