2012/08/01 by Jennifer Schober, D. R. G. Schleicher, Dominik R. G. Schleicher +7 · 1 citation
Physics and Astronomy · #Astrophysics #Astrophysics and Star Formation Studies #Classical mechanics #Dynamo #Dynamo theory #Kinetic energy #Magnetic Reynolds number #Magnetic energy #Magnetic field #Magnetization #Magnetohydrodynamic turbulence #Magnetohydrodynamics #Mechanics #Physics #Quantum mechanics #Reynolds number #Solar and Space Plasma Dynamics #Stellar, planetary, and galactic studies #Turbulence #Turbulence kinetic energy #astro-ph.CO #physics.plasm-ph
paper · pdf · doi:10.1017/s1743921313002585
published in Proceedings of the International Astronomical Union 8(S294), 237-248 (Cambridge University Press) · 13 pages, 8 figures, proceedings article for IAUS 294
openalex publication_date 2012/08/01 · arxiv created 2012/10/29 · arxiv updated 2015/06/11 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/05
Abstract The first galaxies form due to gravitational collapse of primordial halos. During this collapse, weak magnetic seed fields get amplified exponentially by the small-scale dynamo - a process converting kinetic energy from turbulence into magnetic energy. We use the Kazantsev theory, which describes the small-scale dynamo analytically, to study magnetic field amplification for different turbulent velocity correlation functions. For incompressible turbulence (Kolmogorov turbulence), we find that the growth rate is proportional to the square root of the hydrodynamic Reynolds number, Re 1/2 . In the case of highly compressible turbulence (Burgers turbulence) the growth rate increases proportional to Re 1/3 . With a detailed chemical network we are able to follow the chemical evolution and determine the kinetic and magnetic viscosities (due to Ohmic and ambipolar diffusion) during the collapse of the halo. This way, we can calculate the growth rate of the small-scale dynamo quantitatively and predict the evolution of the small-scale magnetic field. As the magnetic energy is transported to larger scales on the local eddy-timescale, we obtain an estimate for the magnetic field on the Jeans scale. Even there, we find that equipartition with the kinetic energy is reached on small timescales. Dynamically relevant field structures can thus be expected already during the formation of the first objects in the Universe.