Acceleration and Heating of Interstellar Gas by Cosmic Rays
Abstract
When cosmic rays try to stream along the magnetic field of the Galaxy, they are scattered and must diffuse down a cosmic-ray density gradient. The associated pressure gradient acts on the interstellar gas, with the hydromagnetic waves that cause the scattering acting as a clutch which couples gas and cosmic rays. When the cosmic rays have diffused down a density scale height, they have lost a major fraction of their momentum and energy. Therefore, they may be a major source of the observed interstellar kinetic and thermal energies. This energy transfer is a collective, plasma-physical process that does not ionize the gas. For applications, one must distinguish the cosmic rays that are "engaged by the clutch" from those that are not. The former have energies up to a few GeV and carry much of the energy and pressure of the cosmic rays. The engaged cosmic rays may raise neutral hydrogen several hundred parsecs above spiral arms, as observed. They may aid in star formation. Their confinement to spiral arms helps to explain the pressure balance in inter-arm regions, and perhaps in the galactic halo
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 1971
- DOI:
- 10.1086/150794
- Bibcode:
- 1971ApJ...163..503W