Reflection and Transmission at the Apparent Horizon during Gravitational Collapse

We examine the wave-functionals describing the collapse of a self-gravitating dust ball in an exact quantization of the gravity-dust system. We show that ingoing (collapsing) dust shell modes outside the apparent horizon must necessarily be accompanied by outgoing modes inside the apparent horizon, whose amplitude is suppressed by the square root of the Boltzmann factor at the Hawking temperature. Likewise, ingoing modes in the interior must be accompanied by outgoing modes in the exterior, again with an amplitude suppressed by the same factor. A suitable superposition of the two solutions is necessary to conserve the dust probability flux across the apparent horizon, thus each region contains both ingoing and outgoing dust modes. If one restricts oneself to considering only the modes outside the apparent horizon then one should think of the apparent horizon as a partial reflector, the probability for a shell to reflect being given by the Boltzmann factor at the Hawking temperature determined by the mass contained within it. However, if one considers the entire wave function, the outgoing wave in the exterior is seen to be the transmission through the horizon of the interior outgoing wave that accompanies the collapsing shells. This transmission could allow information from the interior to be transferred to the exterior.Comment: 19 pages, no figures. To appear in Phys. Rev.

General spherically symmetric elastic stars in Relativity

The relativistic theory of elasticity is reviewed within the spherically symmetric context with a view towards the modeling of star interiors possessing elastic properties such as theones expected in neutron stars. Emphasis is placed on generality in the main sections of the paper, and the results are then applied to specific examples. Along the way, a few general results for spacetimes admitting isometries are deduced, and their consequences are fully exploited in the case of spherical symmetry relating them next to the the case in which the material content of the spacetime is some elastic material. This paper extends and generalizes the pioneering work by Magli and Kijowski [1], Magli [2] and [3], and complements, in a sense, that by Karlovini and Samuelsson in their interesting series of papers [4], [5] and [6].Comment: 23 page

Near-Infrared Time-Series Photometry in the Field of Cygnus OB2 Association I - Rotational Scenario For Candidate Members

In the last decades, the early pre main sequence stellar rotational evolution picture has been constrained by studies targeting different young regions at a variety of ages. Observational studies suggest a mass-rotation dependence, and for some mass ranges a connection between rotation and the presence of a circumstellar disk. Not still fully explored, though, is the role of environmental conditions on the rotational regulation. We investigate the rotational properties of candidate members of the young massive association Cygnus OB2. The Stetson variability index, Lomb-Scargle periodogram, Saunders statistics, string/rope length method, and visual verification of folded light curves were applied to select 1224 periodic variable stars. Completeness and contamination of the periodic sample was derived from Monte Carlo simulations, out of which 894 periods were considered reliable. Our study was considered reasonably complete for periods from 2 to 30 days. The general rotational scenario seen in other young regions is confirmed by Cygnus OB2 period distributions, with disked stars rotating on average slower than non-disked stars. A mass-rotation dependence was also verified, but as in NGC 6530, lower mass stars are rotating on average slower than higher mass stars, with an excess of slow rotators among the lower mass population. The effect of the environment on the rotational properties of the association was investigated by re-analysing the results while taking into account the incident UV radiation arising from O stars in the association. Results compatible with the disk-locking scenario were verified for stars with low UV incidence, but no statistical significant relation between rotation and disk presence was verified for stars with high UV incidence suggesting that massive stars can have an important role on regulating the rotation of nearby low mass stars.Comment: Submitted on December 23, 201

Initial data and the end state of spherically symmetric gravitational collapse

Generalizing earlier results on the initial data and the final fate of dust collapse, we study here the relevance of the initial state of a spherically symmetric matter cloud towards determining its end state in the course of a continuing gravitational collapse. It is shown that given an arbitrary regular distribution of matter at the initial epoch, there always exists an evolution from this initial data which would result either in a black hole or a naked singularity depending on the allowed choice of free functions available in the solution. It follows that given any initial density and pressure profiles for the cloud, there is a non-zero measure set of configurations leading either to black holes or naked singularities, subject to the usual energy conditions ensuring the positivity of energy density. We also characterize here wide new families of black hole solutions resulting from spherically symmetric collapse without requiring the cosmic censorship assumption.Comment: Ordinary Tex file, 31 pages no figure

Elastic thick shells in general relativity

It is shown that exact spherically symmetric solutions to Einstein's field equations exist such that, over an open region of the spacetime, they are singularity free, satisfy the dominant energy condition, represent elastic matter with a well-defined constitutive function, and are such that elastic perturbations propagate causally. Two toy models are then built up in which a thick elastic, spherically symmetric shell with the above properties, separates two Robertson-Walker regions corresponding to different values of the curvature k in the first model and to the same value of k in the second model. The junction conditions (continuity of the first and second fundamental forms) are shown to be exactly satisfied across the corresponding matching spherical surfaces.- The authors are grateful to Prof. Raul Vera, from the Universidad del Pais Vasco/Euskal Herriko Unibersitatea, for helpful discussions and suggestions. One of the authors (J. C.) acknowledges financial support from the Spanish Ministerio de Economia y Competitividad through Grants No. FPA2013-41042-P and No. FPA2016-76821-P, and also acknowledges the warm hospitality, and partial financial support, from the University do Minho, where the present version of this manuscript was prepared. The research of I. B. and E. V. was partially financed by Portuguese Funds through FCT (Fundacao para a Ciencia e Tecnologia) within the Project No. UID/MAT/00013/2013. I. B. is grateful for support from FCT, through the Project No. PEstOE/MAT/UI0013/2014 and also expresses her gratitude for the hospitality at the Universitat de les Illes Balears

Busca usando sinônimos no Ainfo-Consulta.

O foco deste trabalho é na expansão de consultas com termos obtidos por meio do Thesaurus Brasileiro de Agricultura - Thesagro (BRASIL, 1999) para melhorar os resultados do Ainfo-Consulta

Dynamical Mass Constraints on Low-Mass Pre-Main-Sequence Stellar Evolutionary Tracks: An Eclipsing Binary in Orion with a 1.0 Msun Primary and an 0.7 Msun Secondary

We report the discovery of a double-lined, spectroscopic, eclipsing binary in the Orion star-forming region. We analyze the system spectroscopically and photometrically to empirically determine precise, distance-independent masses, radii, effective temperatures, and luminosities for both components. The measured masses for the primary and secondary, accurate to ~1%, are 1.01 Msun and 0.73 Msun, respectively; thus the primary is a definitive pre-main-sequence solar analog, and the secondary is the lowest-mass star yet discovered among pre-main-sequence eclipsing binary systems. We use these fundamental measurements to test the predictions of pre-main-sequence stellar evolutionary tracks. None of the models we examined correctly predict the masses of the two components simultaneously, and we implicate differences between the theoretical and empirical effective temperature scales for this failing. All of the models predict the observed slope of the mass-radius relationship reasonably well, though the observations tend to favor models with low convection efficiencies. Indeed, considering our newly determined mass measurements together with other dynamical mass measurements of pre-main-sequence stars in the literature, as well as measurements of Li abundances in these stars, we show that the data strongly favor evolutionary models with inefficient convection in the stellar interior, even though such models cannot reproduce the properties of the present-day Sun.Comment: Accepted by Ap

Herpetofauna, Espora Hydroelectric Power Plant, state of Goiás, Brazil.

We provide a checklist of the herpetofaunal assemblage from Espora Hydroelectric Power Plant region(UHE Espora), southwestern of the state of Goiás, Brazil. Representatives of 32 amphibian and 71 reptile species wereobtained during faunal monitoring and faunal rescue programs carried out in the study area. The obtained species listand distribution records are here discussed in an attempt to improve the still limited knowledge on Cerradoherpetofaunal assemblages