Dynamo effect in unstirred self-gravitating turbulence
arXiv:2112.03838 · doi:10.1093/mnras/stac982
Abstract
In many astrophysical environments, self-gravity can generate kinetic energy, which, in principle, is available for driving dynamo action. Using direct numerical simulations, we show that in unstirred self-gravitating subsonic turbulence with helicity and a magnetic Prandtl number of unity, there is a critical magnetic Reynolds number of about 25 above which the work done against the Lorentz force exceeds the Ohmic dissipation. The collapse itself drives predominantly irrotational motions that cannot be responsible for dynamo action. We find that, with a weak magnetic field, one-third of the work done by the gravitational force goes into compressional heating and the remaining two-thirds go first into kinetic energy of the turbulence before a fraction of it is converted further into magnetic and finally thermal energies. Close to the collapse, however, these fractions change toward 1/4 and 3/4 for compressional heating and kinetic energy, respectively. When the magnetic field is strong, the compressional heating fraction is unchanged. Out of the remaining kinetic energy, one quarter goes directly into magnetic energy via work against the Lorentz force. The fraction of vortical motions diminishes in favor of compressive motions that are almost exclusively driven by the Jeans instability. For an initially uniform magnetic field, field amplification at scales larger than those of the initial turbulence are driven by tangling.
17 pages, 19 figures, 1 table, resubmitted to MNRAS
References in corpus (17)
- Cold streams in early massive hot haloes as the main mode of galaxy formation
- Modeling Collapse and Accretion in Turbulent Gas Clouds: Implementation and Comparison of Sink Particles in AMR and SPH
- Simulations of nonhelical hydromagnetic turbulence
- A new Jeans resolution criterion for (M)HD simulations of self-gravitating gas: Application to magnetic field amplification by gravity-driven turbulence
- What determines the density structure of molecular clouds ? A case study of Orion B with Herschel
- The impact of feedback on cosmological gas accretion
- The sonic scale revealed by the world's largest supersonic turbulence simulation
- Is nonhelical hydromagnetic turbulence peaked at small scales?
- The Turbulent Dynamo in Highly Compressible Supersonic Plasmas
- Mach number dependence of the onset of dynamo action
- Turbulence from localized random expansion waves
- JCMT POL-2 and BISTRO Survey observations of magnetic fields in the L1689 molecular cloud
- Numerical study of large-scale vorticity generation in shear-flow turbulence
- The core and stellar mass functions in massive collapsing filaments
- Nonlinear turbulent dynamo during gravitational collapse
- Primordial magnetic helicity evolution with a homogeneous magnetic field from inflation
- Magnetic Field Orientation in Self-Gravitating Turbulent Molecular Clouds