Magnetic tension and instabilities in the Orion A integral shaped
  filament
  The Orion nebula is a prime example of a massive star-forming region in our
galaxy. Observations have shown that gravitational and magnetic energy are
comparable in its integral shaped filament (ISF) on a scale of ~1 pc, and that
the population of pre-main sequence stars appears dynamically heated compared
to the protostars. These results have been attributed to a slingshot mechanism
resulting from the oscillation of the filament (Stutz & Gould 2016). In this
paper, we show that radially contracting filaments naturally evolve toward a
state where gravitational, magnetic, and rotational energy are comparable.
While the contraction of the filament will preferentially amplify the axial
component of the magnetic field, the presence of rotation leads to a helical
field structure. We show how magnetic tension can give rise to a filament
oscillation, and estimate a typical timescale of 0.7 million years for the
motion of the filament to the position of maximum displacement, consistent with
the characteristic timescale of the ejected stars. Furthermore, the presence of
helical magnetic fields is expected to give rise to magneto-hydrodynamical
instabilities. We show here that the presence of a magnetic field significantly
enhances the overall instability, which operates on a characteristic scale of
about 1 pc. We expect the physics discussed here to be generally relevant in
massive star forming regions, and encourage further investigations in the
future.
