Browsing by Author "Fernandez, Rodrigo"

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    Internal heating and thermal emission from old neutron stars -: Constraints on dense-matter and gravitational physics
    (2007) Reisenegger, Andreas; Fernandez, Rodrigo; Jofre, Paula
    The equilibrium composition of neutron star matter is achieved through weak interactions (direct and inverse beta decays), 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 mechanisms causing such density perturbations: (1) the reduction in centrifugal force caused by spin-down (particularly in millisecond pulsars), leading to rotochemical heating, and (2) a hypothetical time-variation of the gravitational constant, as predicted by some theories of gravity and current cosmological models, leading to gravitochemical heating. If only slow weak interactions are allowed in the neutron star (modified Urca reactions, with or without Cooper pairing), rotochemical heating can account for the observed ultraviolet emission from the closest millisecond pulsar, PSR J0437-4715, which also provides a constraint on vertical bar dG/dt vertical bar of the same order as the best available in the literature.
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    Rotochemical heating of neutron stars
    (2006) Reisenegger, Andreas; Jofre, Paula; Fernandez, Rodrigo; Kantor, Elena
    The electrostatic potential that keeps approximate charge neutrality in neutron star matter is self-consistently introduced into the formalism for "rotochemical heating" presented in a previous paper by Fernandez and Reisenegger. Although the new formalism is more rigorous, we show that its observable consequences are indistinguishable from those of the previous one, leaving the conclusions of the previous paper unchanged.