Evolutions of Magnetized and Rotating Neutron Stars

We study the evolution of magnetized and rigidly rotating neutron stars within a fully general relativistic implementation of ideal magnetohydrodynamics with no assumed symmetries in three spatial dimensions. The stars are modeled as rotating, magnetized polytropic stars and we examine diverse scenarios to study their dynamics and stability properties. In particular we concentrate on the stability of the stars and possible critical behavior. In addition to their intrinsic physical significance, we use these evolutions as further tests of our implementation which incorporates new developments to handle magnetized systems.Comment: 12 pages, 8 figure

Validation of a personal control scale: A specific measure of perceived control expectations in job search

[ES]Los técnicos en orientación profesional necesitan herramientas especializadas para medir la motivación de búsqueda de empleo. Entre los elementos que motivan a una persona a buscar trabajo destacan sus expectativas. Con el objetivo de evaluarlas, se creó la escala de Expectativas de Control Percibido de Búsqueda de Empleo (ECPBE) partiendo del modelo de Expectativas Generalizadas de Control (EGC) de Palenzuela. Se estudia la validez convergente-discriminante, la fiabilidad (consistencia interna y homogeneidad) y la validez factorial. Se obtienen correlaciones con las subescalas próximas teóricamente significativas y se confirma la presencia de cuatro factores para los ítems de autoeficacia, expectativas de éxito, locus de control interno y locus de control externo. Se puede considerar la ECPBE como una escala válida para medir las expectativas propuestas desde el modelo de EGC adaptado a la situación de búsqueda de empleo, presentando un adecuado nivel de homogeneidad y consistencia en la medida. [EN] Experts in career guidance need specialised tools to measure motivation for job search. Among the remarkable elements that motivate a person to search for a job are their own expectations. Aiming at evaluating expectations, the Perceived Control Expectations in Job Search (PCEJS) scale has been created based on Palenzuela's model of Generalized Expectancies of Control (GEC). Convergent-discriminant validity, reliability (internal consistency and homogeneity), and factorial validity are addressed in this study. Correlations are found among theoretically closed sub-scales, and the presence of 4 factors for the items of self-efficacy, expectations of success, internal locus of control and external locus of control is substantiated. The PCEJS can be considered a valid scale to measure expectations as proposed by the GEC model when adapted to a job search situation, showing an appropriate level of homogeneity and consistency in the measurement

Simulating binary neutron stars: dynamics and gravitational waves

We model two mergers of orbiting binary neutron stars, the first forming a black hole and the second a differentially rotating neutron star. We extract gravitational waveforms in the wave zone. Comparisons to a post-Newtonian analysis allow us to compute the orbital kinematics, including trajectories and orbital eccentricities. We verify our code by evolving single stars and extracting radial perturbative modes, which compare very well to results from perturbation theory. The Einstein equations are solved in a first order reduction of the generalized harmonic formulation, and the fluid equations are solved using a modified convex essentially non-oscillatory method. All calculations are done in three spatial dimensions without symmetry assumptions. We use the \had computational infrastructure for distributed adaptive mesh refinement.Comment: 14 pages, 16 figures. Added one figure from previous version; corrected typo

Binary black holes' effects on electromagnetic fields

In addition to producing gravitational waves (GW), the dynamics of a binary black hole system could induce emission of electromagnetic (EM) radiation by affecting the behavior of plasmas and electromagnetic fields in their vicinity. We here study how the electromagnetic fields are affected by a pair of orbiting black holes through the merger. In particular, we show how the binary's dynamics induce a variability in possible electromagnetically induced emissions as well as a possible enhancement of electromagnetic fields during the late-merge and merger epochs. These time dependent features will likely leave their imprint in processes generating detectable emissions and can be exploited in the detection of electromagnetic counterparts of gravitational waves.Comment: 4 pages, 4 figures. Updated to coincide with PRL versio

Critical Phenomena in Neutron Stars I: Linearly Unstable Nonrotating Models

We consider the evolution in full general relativity of a family of linearly unstable isolated spherical neutron stars under the effects of very small, perturbations as induced by the truncation error. Using a simple ideal-fluid equation of state we find that this system exhibits a type-I critical behaviour, thus confirming the conclusions reached by Liebling et al. [1] for rotating magnetized stars. Exploiting the relative simplicity of our system, we are able carry out a more in-depth study providing solid evidences of the criticality of this phenomenon and also to give a simple interpretation of the putative critical solution as a spherical solution with the unstable mode being the fundamental F-mode. Hence for any choice of the polytropic constant, the critical solution will distinguish the set of subcritical models migrating to the stable branch of the models of equilibrium from the set of subcritical models collapsing to a black hole. Finally, we study how the dynamics changes when the numerically perturbation is replaced by a finite-size, resolution independent velocity perturbation and show that in such cases a nearly-critical solution can be changed into either a sub or supercritical. The work reported here also lays the basis for the analysis carried in a companion paper, where the critical behaviour in the the head-on collision of two neutron stars is instead considered [2].Comment: 15 pages, 9 figure

Relativistic MHD with Adaptive Mesh Refinement

This paper presents a new computer code to solve the general relativistic magnetohydrodynamics (GRMHD) equations using distributed parallel adaptive mesh refinement (AMR). The fluid equations are solved using a finite difference Convex ENO method (CENO) in 3+1 dimensions, and the AMR is Berger-Oliger. Hyperbolic divergence cleaning is used to control the $\nabla\cdot {\bf B}=0$ constraint. We present results from three flat space tests, and examine the accretion of a fluid onto a Schwarzschild black hole, reproducing the Michel solution. The AMR simulations substantially improve performance while reproducing the resolution equivalent unigrid simulation results. Finally, we discuss strong scaling results for parallel unigrid and AMR runs.Comment: 24 pages, 14 figures, 3 table