8,078 research outputs found
Rotochemical Heating in Millisecond Pulsars. Formalism and Non-superfluid case
Rotochemical heating originates in a departure from beta equilibrium due to
spin-down compression in a rotating neutron star. The main consequence is that
the star eventually arrives at a quasi-equilibrium state, in which the thermal
photon luminosity depends only on the current value of the spin-down power,
which is directly measurable. Only in millisecond pulsars the spin-down power
remains high long enough for this state to be reached with a substantial
luminosity. We report an extensive study of the effect of this heating
mechanism on the thermal evolution of millisecond pulsars, developing a general
formalism in the slow-rotation approximation of general relativity that takes
the spatial structure of the star fully into account, and using a sample of
realistic equations of state to solve the non-superfluid case numerically. We
show that nearly all observed millisecond pulsars are very likely to be in the
quasi-equilibrium state. Our predicted quasi-equilibrium temperatures for PSR
J0437-4715 are only 20% lower than inferred from observations. Accounting for
superfluidity should increase the predicted value.Comment: 34 pages, 8 figures, AASTeX. Accepted for publication in Ap
Constraining a possible time-variation of the gravitational constant through "gravitochemical heating" of neutron stars
A hypothetical time-variation of the gravitational constant would make
neutron stars expand or contract, so the matter in their interiors would depart
from beta equilibrium. This induces non-equilibrium weak reactions, which
release energy that is invested partly in neutrino emission and partly in
internal heating. Eventually, the star arrives at a stationary state in which
the temperature remains nearly constant, as the forcing through the change of
is balanced by the ongoing reactions. Using the surface temperature of the
nearest millisecond pulsar (PSR J04374715) inferred from ultraviolet
observations and results from theoretical modelling of the thermal evolution,
we estimate two upper limits for this variation: (1) if the fast, "direct Urca" reactions are allowed,
and (2) considering only the
slower, "modified Urca" reactions. The latter is among the most restrictive
upper limits obtained by other methods.Comment: IAU 2009 JD9 conference proceedings. MmSAIt, vol.80, in press. Paolo
Molaro & Elisabeth Vangioni, eds. - 4 pages, 2 figure
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