Cooling of neutrons stars proceeds mainly via neutrino emission;
As an example we study the modified neutrino bremsstrahlung process
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 matrix. We find that
the use of the matrix as compared to previous estimates based upon one pion
exchange leads a substantial reduction of the predicted emissivity.