Cosmic-ray heating of molecular cloud cores
  Cosmic rays are an important source of heating in the interstellar medium, in
particular in dense molecular cloud cores shielded from the external
ultraviolet radiation field. The limits placed on the cosmic-ray ionization
rate from measurements of the gas temperature in dense clouds are unaffected by
the uncertainties associated to the traditional methods based on the analysis
of molecular abundances. However, high-resolution data are required to
determine with sufficient accuracy the spatial temperature distribution within
prestellar cores. In this contribution we illustrate in detail the case of the
well-studied prestellar core L1544, showing that both its thermal structure and
chemical composition are consistent with a cosmic ray ionization rate of $\sim
10^{-17}$~s$^{-1}$, significantly smaller than the value measured in the
diffuse interstellar medium. We also briefly discuss possible applications of
this method to molecular clouds of other galaxies
