The non-isothermal stage of magnetic star formation - II. Results

Matthew W. Kunz, Telemachos Ch Mouschovias

Research output: Contribution to journalArticle

Abstract

In a previous paper we formulated the problem of the formation and evolution of fragments (or cores) in magnetically supported, self-gravitating molecular clouds in axisymmetric geometry, accounting for the effects of ambipolar diffusion and Ohmic dissipation, grain chemistry and dynamics, and radiative transfer. Here, we present results of star formation simulations that accurately track the evolution of a protostellar fragment over 11 orders of magnitude in density (from 300 to ≈ 1014 cm-3), i.e. from the early ambipolar-diffusion-initiated fragmentation phase, through the magnetically supercritical, dynamical-contraction phase and the subsequent magnetic decoupling stage, to the formation of a protostellar core in near hydrostatic equilibrium. As found by Fiedler & Mouschovias, gravitationally-driven ambipolar diffusion leads to the formation and subsequent dynamic contraction of a magnetically supercritical core. Moreover, we find that ambipolar diffusion, not Ohmic dissipation, is responsible for decoupling all the species except the electrons from the magnetic field, by a density of ≈ 3 × 1012 cm-3. Magnetic decoupling precedes the formation of a central stellar object and ultimately gives rise to a concentration of magnetic flux (a 'magnetic wall') outside the hydrostatic core - as also found by Tassis & Mouschovias through a different approach. At approximately the same density at which Ohmic dissipation becomes more important than ambipolar diffusion (>rsim 7 × 1012 cm-3), the grains carry most of the electric charge as well as the electric current. The prestellar core remains disc like down to radii ~ 10 au, inside which thermal pressure becomes important. The magnetic flux problem of star formation is resolved for at least strongly magnetic newborn stars by this stage of the evolution, i.e. by a central density ≈ 1014 cm-3. The hydrostatic core has radius ≈ 2 au, density ≈ 1014 cm-3, temperature ≈ 300 K, magnetic field strength ≈ 0.2 G, magnetic flux ≈ 5 × 1026 Mx, luminosity ~ 10-3 L. and mass ~ 10-2 M..

Original languageEnglish (US)
Pages (from-to)322-341
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Volume408
Issue number1
DOIs
StatePublished - Oct 1 2010

Fingerprint

magnetic stars
ambipolar diffusion
star formation
ohmic dissipation
hydrostatics
dissipation
decoupling
magnetic flux
contraction
magnetic field
fragments
radii
radiative transfer
electric charge
molecular clouds
electric current
fragmentation
magnetic fields
field strength
geometry

Keywords

  • Dust, extinction
  • ISM: clouds
  • MHD
  • Magnetic fields
  • Radiative transfer
  • Stars: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

The non-isothermal stage of magnetic star formation - II. Results. / Kunz, Matthew W.; Mouschovias, Telemachos Ch.

In: Monthly Notices of the Royal Astronomical Society, Vol. 408, No. 1, 01.10.2010, p. 322-341.

Research output: Contribution to journalArticle

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