1201.0509 (James A. McLeman et al.)

Star formation from dark filamentary clouds: Gravitational stability of a cylindrical plasma with an azimuthal and axial magnetic field    [PDF]

James A. McLeman, Charles H. -T. Wang, Robert Bingham

The precise process by which dark filamentary clouds collapse to form stars is a subject of intense debate. In this paper we consider a cylindrical distribution of plasma with both axial and azimuthal magnetic field and examine the resulting gravitational stability. The azimuthal magnetic field is created from an electric current in the plasma and is found to be dictated by Ampere's law. We model this system by using the magnetohydrodynamic (MHD) equation to derive a new virial theorem. We can reduce it to the virial theorem due to Chandrasekhar and Fermi (1953) if we remove the azimuthal magnetic field, as this will represent the case which they have considered. This new virial theorem gives us a fresh insight into the stability of the system. We also derive from this new virial theorem the case where there is only an azimuthal magnetic field. Our generalised stability condition allows for a possible electric current within realistic astronomical values.

View original: http://arxiv.org/abs/1201.0509