Jennifer Schober

A small-scale dynamo, also called turbulent dynamo, is a magnetohydrodynamical process, in which the kinetic energy from turbulence is converted into magnetic energy. The mechanism is based on the fact that the magnetic field becomes stronger when the magnetic flux ropes are stretched. Figure 1 illustrates the stretching, twisting, and folding of the field lines schematically. The trigger of the stretching is turbulence, i.e. chaotic motion on a large range of scales, in a weakly magnetized plasma. I use an analytical description to predict the properties of the turbulent dynamo and the evolution of the magnetic field. My models take into account various astrophysical environments, for example different types of turbulence and different microphysical quantities.

 

 

Besides the analytical description of the small-scale dynamo, a focus of my research is its application to the formation of the first stars and galaxies. Here it might play a distinguished role as turbulence is driven efficiently by accretion and supernova explosions. These turbulent motions stretch the field lines and by this amplify the field exponentially at a typically very large growth rate. With our models we find that strong magnetic fields of the order of 10^-6 Gauss can be generated by the turbulent dynamo which is comparable to the present-day Milky Way value. The amplification takes place within a few 10⁷ years which is short compared to other dynamical timescales of the systems. A typical evolution of the magnetic field strength is shown in figure 2.

Figure 2: The typical time evolution of the magnetic field strength B(t) in the presence of a turbulent dynamo. The magnetic field increases by many orders of magnitude!

 

 

 

 

Related publications:

• Schober, J.; Schleicher, D. R. G.; Federrath, C.; Bovino, S.; Klessen, R. S.:
  “Saturation of the turbulent dynamo”
  (published in “Physical Review E”, Volume 92, Issue 2, id.023010; 08/2015)
• Federrath, C.; Schober, J.; Bovino, S.; Schleicher, D. R. G.:
  “The turbulent dynamo in highly compressible supersonic plasmas”
  (published in “The Astrophysical Journal Letters”, Volume 797, Issue 2, article id. L19, 6 pp.; 12/2014)
• Schober, J.; Schleicher, D. R. G. ; Klessen, R. S.:
  “Magnetic field amplification in young galaxies”
  (published in “Astronomy & Astrophysics”, Volume 560, id.A87, 13 pp; 12/2013)
• Schleicher, D. R. G.; Schober, J.; Federrath, C.; Bovino, S.; Schmidt, W.:
  The small-scale dynamo: Breaking universality at high Mach numbers
  (published in “New Journal of Physics”, Volume 15, Issue 2, article id. 023017; 02/2013)
• Bovino, S.; Schleicher, D. R. G.; Schober, J.:
  Turbulent magnetic field amplification from the smallest to the largest magnetic Prandtl numbers: Implications of the turbulent spectra
  (published in “New Journal of Physics”, Volume 15, Issue 1, article id. 013055; 01/2013)
• Schober, J.; Schleicher, D. R. G.; Bovino, S.; Klessen, R. S.:
  Small-scale dynamo at low magnetic Prandtl numbers
  (published in “Physical Review E”, vol. 86, Issue 6, id. 066412; 12/2012)
• Schober, J.; Schleicher, D. R. G.; Federrath, C.; Glover, S.; Klessen, R. S.; Banerjee, R.:
  The small-scale dynamo and non-ideal magnetohydrodynamics in primordial star formation
  (published in “The Astrophysical Journal”, Volume 754, Issue 2, article id. 99, 9 pp.; 08/2012)
• Schober, J.; Schleicher, D. R. G.; Federrath, C.; Klessen, R. S.; Banerjee, R.:
  Magnetic field amplification by small-scale dynamo action: Dependence on turbulence models and Reynolds and Prandtl numbers
  (published in “Physical Review E”, vol. 85, Issue 2, id. 026303; 02/2012)
• Federrath, C.; Chabrier, G.; Schober, J.; Banerjee, R.; Klessen, R. S.; Schleicher, D. R. G.:
  Mach number dependence of turbulent magnetic field amplification: Solenoidal versus compressive flows
  (published in “Physical Review Letters”, vol. 107, Issue 11, id. 114504; 09/2011)