The cooling of a compact star depends very sensitively on the state of matter at supranuclear den... more The cooling of a compact star depends very sensitively on the state of matter at supranuclear densities, which essentially controls the neutrino emission, as well as on the structure of the stellar outer layers which control the photon emission. Open issues concern the hyperon population, the presence of meson condensates, superfluidity and superconductivity, and the transition of confined hadronic matter to quark matter. This paper describes these issues and presents cooling calculations based on a broad collection of equations of state for neutron star matter and strange matter. These results are tested against the body of observed cooling data.
We study numerically the cooling of a young bare strange star and show that its thermal luminosit... more We study numerically the cooling of a young bare strange star and show that its thermal luminosity, mostly due to e(+)e(-) pair production from the quark surface, may be much higher than the Eddington limit. The mean energy of photons far from the strange star is approximately 10(2) keV or even more. This differs both qualitatively and quantitatively from the thermal emission from neutron stars and provides a definite observational signature for bare strange stars. It is shown that the energy gap of superconducting quark matter may be estimated from the light curves if it is in the range from approximately 0.5 MeV to a few MeV.
Physical review D: Particles and fields, Jan 15, 1988
Possible effects of strangeness condensation, which has been estimated to occur in dense neutron ... more Possible effects of strangeness condensation, which has been estimated to occur in dense neutron matter at densities of 2.3 -3.0 times nuclear matter density, are calculated with special reference to the cooling of the neutron star probably formed in SN1987A. Although the center of the neutron star will cool much faster in the presence of strangeness condensation than through conventional mechanisms, down to T-2)& 10' K at the present time, the heat conductivity of the neutron star is such that it will take at least a few tens of years for effects of this drop in temperature to reach the surface of the neutron star and be observable.
We complete our study of pulsars' non-uniform surface temperature and of its effects on their sof... more We complete our study of pulsars' non-uniform surface temperature and of its effects on their soft X-ray thermal emission. Our previous work had shown that, due to the effect of gravitational lensing, dipolar fields cannot reproduce the strong pulsations observed in the four nearby pulsars for which surface thermal radiation has been detected: PSR 0833-45 (Vela), PSR 0656+14, PSR 0630+178 (Geminga), and PSR 1055-52. Assuming a standard neutron star mass of 1.4 M ⊙ , we show here that the inclusion of a quadrupolar component, if it is suitably oriented, is sufficient to increase substantially the pulsed fraction, P f , up to, or above, the observed values if the stellar radius is 13 km or even 10 km. For models with a radius of 7 km the maximum pulsed fraction obtainable, with (isotropic) blackbody emission, is of the order of 15% for orthogonal rotators (Vela, Geminga and PSR 1055-52) and only 5% for an inclined rotator as PSR 0656+14. Given the observed values, this may indicate that the neutron stars in Geminga and PSR 0656+14 have radii significantly larger than 7 km and, given that very specific quadrupole components are required to increase P f , even radii of the order of 10 km may be unlikely in all four cases. However, effects not included in our study may possibly seriously invalidate this temptative conclusion.
RESUMEN Se ha tratado de asociar a los rayos cósmicos de ultra alta energía (RCUAE) a las fuentes... more RESUMEN Se ha tratado de asociar a los rayos cósmicos de ultra alta energía (RCUAE) a las fuentes más variadas y poderosas que se conocen en el universo. Los estallidos de rayos gamma (ERG) son candidatos naturales. En este trabajo sostenemos que tales rayos cósmicos pueden ser acelerados por ondas electromágneticas de alta amplitud (OEAA), las cuales son creadas al momento en que la aproximación MHD del campo en el viento generado por el generador central del ERG deja de ser valida. En tal situación se considera como generador central a una estrella extraña con rotación diferencial la cual obtiene la estrella al momento en que una estrella de neutrones se transforma en una estrella extraña dentro de un sistema binario de rayos X de baja masa. Las OEAA generadas de esta manera aceleran los iones ligeros a las más altas energías, E = qη∆Φ max , en donde la eficiencia η ∼ 10 −1 da cuenta de todas las posibles perdidas energéticas. De manera alternativa, también consideramos la posibilidad de que una vez formadas, las OEAA se vuelquen entre sí, dando paso así a una turbulencia electromagnética relativisticamente poderosa. Bajoésta suposición, se estima un límite inferior para la eficiencia, η ∼ 10 −2.5 . Debido a su edad, los sistemas binarios de rayos X de baja masa pueden localizarse en regiones de baja densidad de materia interestelar, p. ej., en cúmulos globulares o inclusive en el medio intergaláctico en el caso de los sistemas con un gran movimiento propio; en cuyo caso las perdidas energéticas sufridas por los rayos cósmicos en el medio circundante son evitadas y dichas partículas pueden experimentar el voltage máximo disponible, produciendo eventos que rebasarían inclusive las observaciones existentes.
Como ha sido mostrado con anterioridad, la materia de quarks, y en particular, un plasma de mater... more Como ha sido mostrado con anterioridad, la materia de quarks, y en particular, un plasma de materia de quarks extraños y electrones tiene una frecuencia de plasma relativamente alta (∼ 20 MeV). Entonces, una estrella compacta compuesta deéste material hasta su superficie, i.e., una estrella extraña desnuda, no podría enfriarse por emisión de su radiación termica.
Results from a study of the cooling of neutron stars are presented. The paper uses a variety of e... more Results from a study of the cooling of neutron stars are presented. The paper uses a variety of equations of state and particularly examines the effects of 'exotic' matter (e.g., pion or kaon condensates, quark matter) at the center of the star. The effect of superfluidity in the core and crust is also studied. It is found that in order
We investigate the thermal, magnetic and rotational evolution of isolated neutron stars assuming ... more We investigate the thermal, magnetic and rotational evolution of isolated neutron stars assuming that the dipolar magnetic field is confined to the crust. Our treatment, for the first time, uses a fully general relativistic formalism not only for the thermal but also for the magnetic part, and includes partial general relativistic effects in the rotational part. Due to the fact that the combined evolution depends crucially upon the compactness of the star, three different equations of state have been employed in the calculations. In the absence of general relativistic effects, while upon increasing compactness a decrease of the crust thickness takes place leading into an accelerating field decay, the inclusion of general relativistic effects intend to "decelerate this acceleration". As a consequence we find that, within the crustal field hypothesis, a given equation of state is compatible with the observed distribution of pulsar periods P and period derivativeṖ provided the initial field strength and current location as well as the magnitude of the impurity content are appropriately constrained.
We investigate the influence of different magnetic field configurations on the temperature distri... more We investigate the influence of different magnetic field configurations on the temperature distribution in neutron star crusts. We consider axisymmetric dipolar fields which are either restricted to the stellar crust, "crustal fields", or allowed to penetrate the core, "core fields". By integrating the two-dimensional heat transport equation in the crust, taking into account the classical (Larmor) anisotropy of the heat conductivity, we obtain the crustal temperature distribution, assuming an isothermal core. Including classical and quantum magnetic field effects in the envelope as a boundary condition, we deduce the corresponding surface temperature distributions. We find that core fields result in practically isothermal crusts unless the surface field strength is well above 10 15 G while for crustal fields with surface strength above a few times 10 12 G significant deviations from crustal isothermality occur at core temperatures inferior or equal to 10 8 K. At the stellar surface, the cold equatorial region produced by the suppression of heat transport perpendicular to the field by the Larmor rotation of the electrons in the envelope, present for both core and crustal fields, is significantly extended by that classical suppression at higher densities in the case of crustal fields. This can result, for crustal fields, in two small warm polar regions which will have observational consequences: the neutron star has a small effective thermally emitting area and the X-ray pulse profiles are expected to have a distinctively different shape compared to the case of a neutron star with a core field. These features, when compared with X-ray data on thermal emission of young cooling neutron stars, would provide a first step toward a new way of studying the magnetic flux distribution within a neutron star.
The cooling of a compact star depends very sensitively on the state of matter at supranuclear den... more The cooling of a compact star depends very sensitively on the state of matter at supranuclear densities, which essentially controls the neutrino emission, as well as on the structure of the stellar outer layers which control the photon emission. Open issues concern the hyperon population, the presence of meson condensates, superfluidity and superconductivity, and the transition of confined hadronic matter to quark matter. This paper describes these issues and presents cooling calculations based on a broad collection of equations of state for neutron star matter and strange matter. These results are tested against the body of observed cooling data.
We study numerically the cooling of a young bare strange star and show that its thermal luminosit... more We study numerically the cooling of a young bare strange star and show that its thermal luminosity, mostly due to e(+)e(-) pair production from the quark surface, may be much higher than the Eddington limit. The mean energy of photons far from the strange star is approximately 10(2) keV or even more. This differs both qualitatively and quantitatively from the thermal emission from neutron stars and provides a definite observational signature for bare strange stars. It is shown that the energy gap of superconducting quark matter may be estimated from the light curves if it is in the range from approximately 0.5 MeV to a few MeV.
Physical review D: Particles and fields, Jan 15, 1988
Possible effects of strangeness condensation, which has been estimated to occur in dense neutron ... more Possible effects of strangeness condensation, which has been estimated to occur in dense neutron matter at densities of 2.3 -3.0 times nuclear matter density, are calculated with special reference to the cooling of the neutron star probably formed in SN1987A. Although the center of the neutron star will cool much faster in the presence of strangeness condensation than through conventional mechanisms, down to T-2)& 10' K at the present time, the heat conductivity of the neutron star is such that it will take at least a few tens of years for effects of this drop in temperature to reach the surface of the neutron star and be observable.
We complete our study of pulsars' non-uniform surface temperature and of its effects on their sof... more We complete our study of pulsars' non-uniform surface temperature and of its effects on their soft X-ray thermal emission. Our previous work had shown that, due to the effect of gravitational lensing, dipolar fields cannot reproduce the strong pulsations observed in the four nearby pulsars for which surface thermal radiation has been detected: PSR 0833-45 (Vela), PSR 0656+14, PSR 0630+178 (Geminga), and PSR 1055-52. Assuming a standard neutron star mass of 1.4 M ⊙ , we show here that the inclusion of a quadrupolar component, if it is suitably oriented, is sufficient to increase substantially the pulsed fraction, P f , up to, or above, the observed values if the stellar radius is 13 km or even 10 km. For models with a radius of 7 km the maximum pulsed fraction obtainable, with (isotropic) blackbody emission, is of the order of 15% for orthogonal rotators (Vela, Geminga and PSR 1055-52) and only 5% for an inclined rotator as PSR 0656+14. Given the observed values, this may indicate that the neutron stars in Geminga and PSR 0656+14 have radii significantly larger than 7 km and, given that very specific quadrupole components are required to increase P f , even radii of the order of 10 km may be unlikely in all four cases. However, effects not included in our study may possibly seriously invalidate this temptative conclusion.
RESUMEN Se ha tratado de asociar a los rayos cósmicos de ultra alta energía (RCUAE) a las fuentes... more RESUMEN Se ha tratado de asociar a los rayos cósmicos de ultra alta energía (RCUAE) a las fuentes más variadas y poderosas que se conocen en el universo. Los estallidos de rayos gamma (ERG) son candidatos naturales. En este trabajo sostenemos que tales rayos cósmicos pueden ser acelerados por ondas electromágneticas de alta amplitud (OEAA), las cuales son creadas al momento en que la aproximación MHD del campo en el viento generado por el generador central del ERG deja de ser valida. En tal situación se considera como generador central a una estrella extraña con rotación diferencial la cual obtiene la estrella al momento en que una estrella de neutrones se transforma en una estrella extraña dentro de un sistema binario de rayos X de baja masa. Las OEAA generadas de esta manera aceleran los iones ligeros a las más altas energías, E = qη∆Φ max , en donde la eficiencia η ∼ 10 −1 da cuenta de todas las posibles perdidas energéticas. De manera alternativa, también consideramos la posibilidad de que una vez formadas, las OEAA se vuelquen entre sí, dando paso así a una turbulencia electromagnética relativisticamente poderosa. Bajoésta suposición, se estima un límite inferior para la eficiencia, η ∼ 10 −2.5 . Debido a su edad, los sistemas binarios de rayos X de baja masa pueden localizarse en regiones de baja densidad de materia interestelar, p. ej., en cúmulos globulares o inclusive en el medio intergaláctico en el caso de los sistemas con un gran movimiento propio; en cuyo caso las perdidas energéticas sufridas por los rayos cósmicos en el medio circundante son evitadas y dichas partículas pueden experimentar el voltage máximo disponible, produciendo eventos que rebasarían inclusive las observaciones existentes.
Como ha sido mostrado con anterioridad, la materia de quarks, y en particular, un plasma de mater... more Como ha sido mostrado con anterioridad, la materia de quarks, y en particular, un plasma de materia de quarks extraños y electrones tiene una frecuencia de plasma relativamente alta (∼ 20 MeV). Entonces, una estrella compacta compuesta deéste material hasta su superficie, i.e., una estrella extraña desnuda, no podría enfriarse por emisión de su radiación termica.
Results from a study of the cooling of neutron stars are presented. The paper uses a variety of e... more Results from a study of the cooling of neutron stars are presented. The paper uses a variety of equations of state and particularly examines the effects of 'exotic' matter (e.g., pion or kaon condensates, quark matter) at the center of the star. The effect of superfluidity in the core and crust is also studied. It is found that in order
We investigate the thermal, magnetic and rotational evolution of isolated neutron stars assuming ... more We investigate the thermal, magnetic and rotational evolution of isolated neutron stars assuming that the dipolar magnetic field is confined to the crust. Our treatment, for the first time, uses a fully general relativistic formalism not only for the thermal but also for the magnetic part, and includes partial general relativistic effects in the rotational part. Due to the fact that the combined evolution depends crucially upon the compactness of the star, three different equations of state have been employed in the calculations. In the absence of general relativistic effects, while upon increasing compactness a decrease of the crust thickness takes place leading into an accelerating field decay, the inclusion of general relativistic effects intend to "decelerate this acceleration". As a consequence we find that, within the crustal field hypothesis, a given equation of state is compatible with the observed distribution of pulsar periods P and period derivativeṖ provided the initial field strength and current location as well as the magnitude of the impurity content are appropriately constrained.
We investigate the influence of different magnetic field configurations on the temperature distri... more We investigate the influence of different magnetic field configurations on the temperature distribution in neutron star crusts. We consider axisymmetric dipolar fields which are either restricted to the stellar crust, "crustal fields", or allowed to penetrate the core, "core fields". By integrating the two-dimensional heat transport equation in the crust, taking into account the classical (Larmor) anisotropy of the heat conductivity, we obtain the crustal temperature distribution, assuming an isothermal core. Including classical and quantum magnetic field effects in the envelope as a boundary condition, we deduce the corresponding surface temperature distributions. We find that core fields result in practically isothermal crusts unless the surface field strength is well above 10 15 G while for crustal fields with surface strength above a few times 10 12 G significant deviations from crustal isothermality occur at core temperatures inferior or equal to 10 8 K. At the stellar surface, the cold equatorial region produced by the suppression of heat transport perpendicular to the field by the Larmor rotation of the electrons in the envelope, present for both core and crustal fields, is significantly extended by that classical suppression at higher densities in the case of crustal fields. This can result, for crustal fields, in two small warm polar regions which will have observational consequences: the neutron star has a small effective thermally emitting area and the X-ray pulse profiles are expected to have a distinctively different shape compared to the case of a neutron star with a core field. These features, when compared with X-ray data on thermal emission of young cooling neutron stars, would provide a first step toward a new way of studying the magnetic flux distribution within a neutron star.
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