  Cooling of neutrons stars proceeds mainly via neutrino emission;
  As an example we study the modified neutrino bremsstrahlung process $nn \to
nn\nu\bar{\nu}.$
  The radiated energy is small compared to other scales in the system.
  Hence one can use low-energy theorems to compute the neutrino emissivity in
terms of the non-radiative process, ie the on-shell $T$ matrix. We find that
the use of the $T-$matrix as compared to previous estimates based upon one pion
exchange leads a substantial reduction of the predicted emissivity.
