On the role of magnetic fields in star formation |
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| Affiliation: | 1. Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK;2. Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK;1. Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Moscow Region, Russia;2. Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Correo Central, Santiago, Chile;1. Astrophysical Sciences Division, Bhabha Atomic Research Centre, Mumbai 400 085, India;2. Homi Bhabha National Institute, Anushaktinagar, Mumbai 400 094, India;1. Laboratório Nacional de Astrofísica, Rua Estados Unidos, 154, CEP, Itajubá, MG 37504-364 Brazil;2. CBA Wisconsin, Luckydog Observatory, 65027 Howath Road, de Soto, WI 54624, USA;3. CBA Concord, 1730 Helix Ct., Concord, CA 94518, USA;4. CBA Ontario, Newcastle Observatory, 9 Laking Drive, Newcastle, ON L1B 1M5, Canada;5. AAVSO, Rolling Hills Observatory, 1643 Nightfall Drive, Clermont, FL 34711, USA;6. CBA Oregon, Jack Jones Observatory, 22665 Bents Road NE, Aurora, OR 97002, USA;7. CBA Wilts, 2 Spa Close, Highworth, Swingdon SN6 7PJ, UK;8. CBA Sierras, Sierra Remote Observatories, 44325 Alder Heights Road, Auberry, CA 93602, USA;9. CBA Illinois, Northbrook Meadow Observatory, 855 Fair Lane, Northbrook, IL 60062, USA |
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| Abstract: | Magnetic fields are observed in star forming regions. However simulations of the late stages of star formation that do not include magnetic fields provide a good fit to the properties of young stars including the initial mass function (IMF) and the multiplicity. We argue here that the simulations that do include magnetic fields are unable to capture the correct physics, in particular the high value of the magnetic Prandtl number, and the low value of the magnetic diffusivity. The artificially high (numerical and uncontrolled) magnetic diffusivity leads to a large magnetic flux pervading the star forming region. We argue further that in reality the dynamics of high magnetic Prandtl number turbulence may lead to local regions of magnetic energy dissipation through reconnection, meaning that the regions of molecular clouds which are forming stars might be essentially free of magnetic fields. Thus the simulations that ignore magnetic fields on the scales on which the properties of stellar masses, stellar multiplicities and planet-forming discs are determined, may be closer to reality than those which include magnetic fields, but can only do so in an unrealistic parameter regime. |
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