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Register a new userJoule heating in the cooling of magnetized neutron stars
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Deborah Nancy Aguilera
Publication date
2007
fields
Physics
and research's language is
English
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We present 2D simulations of the cooling of neutron stars with strong magnetic fields (B geq 10^{13} G). We solve the diffusion equation in axial symmetry including the state of the art microphysics that controls the cooling such as slow/fast neutrino processes, superfluidity, as well as possible heating mechanisms. We study how the cooling curves depend on the the magnetic field strength and geometry. Special attention is given to discuss the influence of magnetic field decay. We show that Joule heating effects are very large and in some cases control the thermal evolution. We characterize the temperature anisotropy induced by the magnetic field for the early and late stages of the evolution of isolated neutron stars.
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We present two-dimensional simulations for the cooling of neutron stars with strong magnetic fields (B > 1e13 Gauss). We study how the cooling curves are influenced by magnetic field decay. We show that the Joule heating effects are very large and in some cases control the thermal evolution. We characterize the temperature anisotropy induced by the magnetic field and predict the surface temperature distribution for the early and late stages of the evolution of isolated neutron stars, comparing our results with available observational data of isolated neutron stars.
Context: Many thermally emitting isolated neutron stars have magnetic fields larger than 10^13 G. A realistic cooling model that includes the presence of high magnetic fields should be reconsidered. Aims: We investigate the effects of anisotropic temperature distribution and Joule heating on the cooling of magnetized neutron stars. Methods: The 2D heat transfer equation with anisotropic thermal conductivity tensor and including all relevant neutrino emission processes is solved for realistic models of the neutron star interior and crust. Results: The presence of the magnetic field affects significantly the thermal surface distribution and the cooling history during both, the early neutrino cooling era and the late photon cooling era. Conclusions: There is a large effect of the Joule heating on the thermal evolution of strongly magnetized neutron stars. Both magnetic fields and Joule heating play a key role in keeping magnetars warm for a long time. Moreover, this effect is important for intermediate field neutron stars and should be considered in radio-quiet isolated neutron stars or high magnetic field radio-pulsars.
We report on a new mechanism for heat conduction in the neutron star crust. We find that collective modes of superfluid neutron matter, called superfluid phonons (sPhs), can influence heat conduction in magnetized neutron stars. They can dominate the heat conduction transverse to magnetic field when the magnetic field $B gsim 10^{13}$ G. At density $rho simeq 10^{12}-10^{14} $ g/cm$^3$ the conductivity due to sPhs is significantly larger than that due to lattice phonons and is comparable to electron conductivity when temperature $simeq 10^8$ K. This new mode of heat conduction can limit the surface anisotropy in highly magnetized neutron stars. Cooling curves of magnetized neutron stars with and without superfluid heat conduction could show observationally discernible differences.
We study thermal structure and evolution of magnetars as cooling neutron stars with a phenomenological heat source in a spherical internal layer. We explore the location of this layer as well as the heating rate that could explain high observable thermal luminosities of magnetars and would be consistent with the energy budget of neutron stars. We conclude that the heat source should be located in an outer magnetars crust, at densities rho < 5e11 g/cm^3, and should have the heat intensity of the order of 1e20 erg/s/cm^3. Otherwise the heat energy is mainly emitted by neutrinos and cannot warm up the surface.
This paper provides an overview of the possible role of Quantum Chromo Dynamics (QDC) for neutron stars and strange stars. The fundamental degrees of freedom of QCD are quarks, which may exist as unconfined (color superconducting) particles in the cores of neutron stars. There is also the theoretical possibility that a significantly large number of up, down, and strange quarks may settle down in a new state of matter known as strange quark matter, which, by hypothesis, could be more stable than atomic nuclei. In the latter case new classes of self-bound, color superconducting objects, ranging from strange quark nuggets to strange quark stars, should exist. The properties of such objects will be reviewed along with the possible existence of deconfined quarks in neutron stars. Implications for observational astrophysics are pointed out.
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