  We establish bounds on the maximum possible specific latent heat of cold
neutron-star matter derived from hadron physics alone. Existing chiral
perturbation theory computations for the equation of state, together with
perturbative Quantum Chromodynamics, relevant at highest densities (even if
they would turn out not to be physically realizable) bind the maximum latent
heat which is possible in actual neutron stars. Because these are already near
gravitational collapse in General Relativity, no denser form of cold matter can
exist: thus, the bounds are a generic physical limit. Even in scenarios that
modify the theory of gravity, the existence of a family of latent-heat maxima
is relevant to diagnose progress in the knowledge of the equation of state of
neutron matter, by quantifying the maximum possible (presumed) phase transition
that its error bands would allow. Thus, latent heat is a natural benchmark for
the equation of state in cold QCD.
