Spectrum of the Galactic Magnetic Fields
Abstract
The magnetic fields observed in the galactic disc are generated by the differential rotation and the helical turbulent motions of interstellar gas. On the scalesl=2πk -1 which lie in the intervall 0<l<l e (l 0≃100 pc is the energy-range scale of the galactic turbulence), the spectral density of the kinetic energy of turbulence (∝k -5/3) exceeds the magnetic energy spectral density (∝k -1). The equipartition between magnetic and kinetic energies is reached atl=l e ≃6 pc in the intercloud medium and is maintained down to the scalel=l d ≃0.03 pc. In dense interstellar cloudsl e is determined by the individual cloud size andl d ≃0.1 pc.The internal turbulent velocities in H i clouds (cloud size is assumed to be 10 pc) lie in the range from 1.8 to 5.6km s-1, fitting well within the observed range of internal rms velocities. Dissipation of the interstellar MHD turbulence leads to creation of temperature fluctuations with amplitudes of 150 K and 65 K in dense clouds and intercloud medium, respectively. The small-scale fluctuations observed in the interstellar medium may arise from such perturbations due to the thermal instability, for instance. Dissipation of the MHD turbulence energy provides nearly half of the energy supply needed to maintain the thermal balance of the interstellar medium.
- Publication:
-
Astrophysics and Space Science
- Pub Date:
- March 1982
- DOI:
- 10.1007/BF00651446
- Bibcode:
- 1982Ap&SS..82..397R
- Keywords:
-
- Disk Galaxies;
- Galactic Structure;
- Hydrogen Clouds;
- Interstellar Magnetic Fields;
- Angular Velocity;
- Energy Spectra;
- Gas Temperature;
- Interstellar Gas;
- Kinetic Energy;
- Magnetohydrodynamics;
- Rotating Fluids;
- Statistical Analysis;
- Turbulent Flow;
- Velocity Distribution;
- Astrophysics