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Internal dissipation through beta processes and thermal emission from old neutron stars ``rotochemical heating'' constraints on a time-variation of Newton's ``constant'' of gravity

Andreas Reisenegger

Pontificia Universidad Catolica de Chile (PUC)

Abstract:

The equilibrium composition of neutron star matter is achieved through weak interactions, which proceed on relatively long time scales. If the density of a matter element is perturbed, it will relax to the new chemical equilibrium through non-equilibrium reactions, which produce entropy that is partly released through neutrino emission, while a similar fraction heats the matter and is eventually radiated as thermal photons. We examined two possible causes of such density perturbations: 1)the reduction in centrifugal force caused by spin-down (particularly in millisecond pulsars), leading to ``rotochemical heating'' (astro-ph/0502116), and 2)a hypothetical time-variation of the gravitational ``constant'', as predicted by some theories of gravity and current cosmological models (``gravitochemical heating''). If only slow weak interactions are allowed in the neutron star (modified Urca reactions, with or without Cooper pairing), ``rotochemical heating'' can roughly account for the observed ultraviolet emission from the closest millisecond pulsar, PSR J0437-4715, which also provides a constraint on |dG/dt| of the same order as the best available in the literature.

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