Magnetic fields catalyse massive black hole formation and growth

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  • Mitchell C Begelman
    JILA, University of Colorado and National Institute of Standards and Technology , 440 UCB, Boulder, CO 80309-0440 , USA
  • Joseph Silk
    Institut d’Astrophysique de Paris, Sorbonne Universités , UPMC Univ. Paris 06 et CNRS, UMR 7095, F-75014 Paris , France

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<jats:title>ABSTRACT</jats:title> <jats:p>Large-scale magnetic fields in the nuclear regions of protogalaxies can promote the formation and early growth of supermassive black holes (SMBHs) by direct collapse and magnetically boosted accretion. Turbulence associated with gravitational infall and star formation can drive the rms field strength toward equipartition with the mean gas kinetic energy; this field has a generic tendency to self-organize into large coherent structures. If the poloidal component of the field (relative to the rotational axis of a star-forming disc) becomes organized on scales ≲r and attains an energy of order a few per cent of the turbulent energy in the disc, then dynamo effects are expected to generate magnetic torques capable of increasing the inflow speed and thickening the disc. The accretion flow can transport matter towards the centre of mass at a rate adequate to create and grow a massive direct-collapse black hole seed and fuel the subsequent AGN at a high rate, without becoming gravitationally unstable. Fragmentation and star formation are thus suppressed and do not necessarily deplete the mass supply for the accretion flow, in contrast to prevailing models for growing and fuelling SMBHs through disc accretion.</jats:p>

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