Turbulence-induced magnetic fields and structure of cosmic ray modified shocks

A. Beresnyak, T. W. Jones, A. Lazarian

Research output: Contribution to journalArticlepeer-review

82 Scopus citations


We propose a model for diffusive shock acceleration (DSA) in which stochastic magnetic fields in the shock precursor are generated through purely fluid mechanisms of a so-called small-scale dynamo. This contrasts with previous DSA models that considered magnetic fields amplified through cosmic ray (CR) streaming instabilities, i.e., either by way of individual particles resonant scattering in the magnetic fields, or by macroscopic electric currents associated with large-scale CR streaming. Instead, in our picture, the solenoidal velocity perturbations that are required for the dynamo to work are produced through the interactions of the pressure gradient of the CR precursor and density perturbations in the inflowing fluid. Our estimates show that this mechanism provides fast growth of magnetic field and is very generic. We argue that for supernovae shocks the mechanism is capable of generating upstream magnetic fields that are sufficiently strong for accelerating CRs up to around 1016 eV. No action of any other mechanism is necessary.

Original languageEnglish (US)
Pages (from-to)1541-1549
Number of pages9
JournalAstrophysical Journal
Issue number2
StatePublished - 2009


  • Acceleration of particles
  • Cosmic rays
  • MHD
  • Scattering
  • Shock waves
  • Turbulence


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