Nuclear spin relaxation within interstellar grains

A. Lazarian, B. T. Draine

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61 Scopus citations


We identify a new mechanism of internal dissipation of rotational kinetic energy in spinning dust grains, arising from the reorientation of nuclear angular momentum, e.g., spins of protons. Grain rotation induces magnetization of the nuclear spin system, with net alignment of nuclear spins parallel to the grain angular velocity. When the grain does not rotate around a principal axis, the nuclear magnetization vector precesses in grain-body coordinates, resulting in dissipation of energy. The analogous process involving electron spins was discovered by E. M. Purcell and termed "Barnett relaxation." We revisit the physics of the Barnett relaxation process and correct the estimate for the Barnett relaxation rate. We show that nuclear relaxation can be orders of magnitude more important than Barnett relaxation. This finding implies that the processes of "thermal flipping" and "thermal trapping" are important for a broad range of grain sizes.

Original languageEnglish (US)
Pages (from-to)L67-L70
JournalAstrophysical Journal
Issue number1 PART 2
StatePublished - Jul 20 1999

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Atomic processes
  • Dust, extinction
  • ISM: magnetic fields
  • Polarization


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