  Driven by the loss of energy, isolated rotating neutron stars (pulsars) are
gradually slowing down to lower frequencies, which increases the tremendous
compression of the matter inside of them. This increase in compression changes
both the global properties of rotating neutron stars as well as their hadronic
core compositions. Both effects may register themselves observationally in the
thermal evolution of such stars, as demonstrated in this Letter. The
rotation-driven particle process which we consider here is the direct Urca (DU)
process, which is known to become operative in neutron stars if the number of
protons in the stellar core exceeds a critical limit of around 11% to 15%. We
find that neutron stars spinning down from moderately high rotation rates of a
few hundred Hertz may be creating just the right conditions where the DU
process becomes operative, leading to an observable effect (enhanced cooling)
in the temperature evolution of such neutron stars. As it turns out, the
rotation-driven DU process could explain the unusual temperature evolution
observed for the neutron star in Cas A, provided the mass of this neutron star
lies in the range of 1.5 to 1.9 \msun and its rotational frequency at birth was
between 40 (400 Hz) and 70% (800 Hz) of the Kepler (mass shedding) frequency,
respectively.
