Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Deviations from Chemical Equilibrium due to Spin-Down as an Internal
  Heat Source in Neutron Stars   The core of a neutron star contains several species of particles, whose
relative equilibrium concentrations are determined by the local density. As the
star spins down, its centrifugal force decreases continuously, and the star
contracts. The density of any given fluid element increases, changing its
chemical equilibrium state. The relaxation towards the new equilibrium takes a
finite time, so the matter is not quite in chemical equilibrium, and energy is
stored that can be released by reactions. For a neutron star core composed of
neutrons (n), protons (p), and electrons (e), the departure from chemical
equilibrium is quantified by the chemical potential difference $\delta\mu\equiv
\mu_{\rm p}+\mu_{\rm e} -\mu_{\rm n}$. A finite $\delta\mu$ increases the
reaction rates and the neutrino emissivity. If large enough ($|\delta\mu|\gta
5kT$), it reduces the net cooling rate because some of the stored chemical
energy is converted into thermal energy, and can even lead to net heating. A
simple model shows the effect of this heating mechanism on the thermal
evolution of neutron stars. It is particularly noticeable for old, rapidly
spinning stars with weak magnetic fields. Observational consequences for
millisecond pulsars are discussed.

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The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
30
The categories of this paper are: q-alg
34
The categories of this paper are: chem-ph
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The categories of this paper are: cs
20
The categories of this paper are: acc-phys
2
The categories of this paper are: math
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
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The categories of this paper are: eess
32
The categories of this paper are: atom-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: nucl-ex
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The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an